Up-conversion.

[Geoffrey Mackenzie-Kennedy-2]

Jim,

I omitted to add this thought in my e-mail to you.

There is an alternative to the usual type of single down conversion and
double (up - down) conversion receiver, which is a single up-conversion
receiver using a lowish VHF IF and detector. The benefits of up-conversion
are then available from a relatively simple architecture. Certainly the cost
of good narrowband VHF filters remains, but it is offset to a large extent
by the removal of a second IF and its filters. Who knows, the cost of good
VHF filters could well come down if more were used.

73,
Geoff
GM4ESD

 



_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N2EY]

In a message dated 8/11/06 7:18:34 AM Eastern Daylight Time,
[hidden email] writes:


> There is an alternative to the usual type of single down conversion and
> double (up - down) conversion receiver, which is a single up-conversion
> receiver using a lowish VHF IF and detector.

Can really good CW filters be made for VHF? By "really good", I mean, say,
400 Hz bandwidth, less than 6 dB loss, 6:60 dB shape factor less than 3 to 1?

What about stability over the temperature range?


 The benefits of up-conversion
>
> are then available from a relatively simple architecture.

The only real advantage I see is a small reduction in spurious responses,
caused by being able to have the low-order spurs be way up in the VHF, and those
which are HF become quite high-order.

A secondary advantage is GC receive.

 Certainly the cost
>
> of good narrowband VHF filters remains, but it is offset to a large extent
> by the removal of a second IF and its filters. Who knows, the cost of good
> VHF filters could well come down if more were used.
>

How much more do VHF filters cost?

Note that if you can live without IF shift, or if you implement IF shift by
different means such as simultaneously pulling the BFO and LO  in equal but
opposite amounts, the single-IF approach of the K2 leaves little to be desired.

Perhaps the big question is this:

Could a rig as good or better than the K2 be implemented using a different
architecture *without* a serious increase in price or power drain, without
losing the "user build- and service-ability" of that rig?

73 de Jim, N2EY
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

> Can really good CW filters be made for VHF? By "really good", I mean,
> say, 400 Hz bandwidth, less than 6 dB loss, 6:60 dB shape factor less
> than 3 to 1?
>
> What about stability over the temperature range?
>
>
>  
Going to be difficult.

 From filter theory (see, e.g., Zverev) we know that the crystal Q and
the filter fractional bandwidth are  related by the equation:

qx = (delta fs/f0)*Qx

where:
qx is the normalized Q in Zverev's prototype low pass filter table
delta fs is the flter bandwidth
f0 is the filter center frequency
Qx is the individual crystal Q needed to construct the filter.


I'll leave the details to the interested reader, but I plugged in these
requirements (6 dB loss, 400 Hz bandwidth and 3:1 or better shape
factor) into the equations and tables for a few typical designs, all at
45 MHz, a common IF frequency. (Go higher and the problem is
proportionally worse; and you can't go much lower and still have an
up-converting design for a maximum receiver frequency of 30 MHz.)

The results call for crystal Qs in the order of 1.5 million to 2.5
million, depending on the number of filter sections and design type.

I've measured quite a few crystals in the process of building and
testing about 20 crystal filters for my pandapter design. The highest Q
crystals I've found (these are all HC-49 case microprocessor crystals of
the inexpensive variety) run around 100K to 110K, and a more typical
value is 80K to 90K. I've also measured about 10% of a batch of
microprocessor crystals as having Qs in the 30-40K range. Still
perfectly OK for an oscillator but not so good for a low loss crystal
filter. (If you go to a crystal manufacturer and purchase custom
crystals for filter purposes, I believe you may see Qs closer to 200K if
you are willing to pay for them.)

Now those Q values are perfectly adequate for a decent filter at 8 MHz,
but are an order of magnitude or more short of adequate for a 45 MHz
narrow band filter.

Crystals with Qs in the 106 range are possible and have been built, but
the are not cheap and I don't know if they are available in the desired
frequency range.

I have also not looked at issues related to the ratio of holder
capacitance to motional capacitance and some other design
considerations, as the minimum Qx seems to be a show stopper.

There are some many practical problems with the holder capacitance,
stray capacitance and the like that would make such a filter
challenging, even if someone were to deliver a box of 45 MHz crystals
with measured Qs of 2 million to my doorstep. And if  the box of
crystals arrive, to obtain frequency stability might require stabilizing
the filter assembly in a temperature controlled oven.

The typical roofing filters at 45 MHz have a bandwidth of 20 KHz or so.
Thus the fractional bandwidth is 50 times larger and the Qx is down into
the 100K range, making these filters relatively easy to realize.


Jack K8ZOA
www.cliftonlaboratories.com

>  
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Geoffrey Mackenzie-Kennedy-2]

> There are some many practical problems with the holder capacitance,
> stray capacitance and the like that would make such a filter challenging,
> even if someone were to deliver a box of 45 MHz crystals with measured Qs
> of 2 million to my doorstep. And if  the box of crystals arrive, to obtain
> frequency stability might require stabilizing the filter assembly in a
> temperature controlled oven.
>
> The typical roofing filters at 45 MHz have a bandwidth of 20 KHz or so.
> Thus the fractional bandwidth is 50 times larger and the Qx is down into
> the 100K range, making these filters relatively easy to realize.

--------------------------------------------------------------------------

An interesting 42.5 MHz filter design appeared several years ago using just
four crystals in ladder configuration. The designer was not looking for
narrow bandwidth nor good shape factor, but illustrating a "method". The
bandwidth was 5 kHz, the shape factor was 4, stopband better than 80db and
the response was symmetrical. In addition to the usual inductors across each
crystal to take care of holder capacitance, as inspired by Zobel, two other
other modifications were incorporated. (1) Parallel tuned circuits were
placed at each end to prevent degeneration into a poor Cauer lowpass filter.
(2) Parallel tuned circuits were used as coupling elements, presumably to
tweak mesh frequencies. Insertion loss unknown, but a fair number of
elements to compensate for temperature change.

73,
Geoff
GM4ESD





_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

Just a short reminder that if you are planning to purchase a Z90 or Z91
panadapter kit, the deadline to drop me an E-mail message is Friday,
August 18th.

A few days after the 18th, I will order enough of the expensive
volume-sensitive parts (enclosures, LCD, PCB) to meet the order
requirements, to provide for two or three units for my use and to
provide a small quantity for spare parts support. This means that if you
miss the August 18th cut-off date, you will have to wait until the next
batch build, which may be a rather long time.

I can accept orders for small things, such as the interface boards,
after the deadline date, up until I actually order those components.

73 de Jack K8ZOA
www.cliftonlaboratories.com
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

Yes, exactly. The minimum required Q scales proportionally to the
fractional bandwidth. Hence at a given frequency the required 400 Hz
filter demands resonator Q's 12.5 times higher than for a 5 KHz filter,
assuming a bunch of other factors remain constant. They don't, but this
is a good enough approximation for our purpose of a back-of-the-envelope
discussion.

Hence, the resonator Q requirements for a 5 KHz filter at 40 MHz are not
grossly different than for a 500 Hz filter at 4 MHz, which is quite
achievable. But for a 400 Hz filter at 45 MHz, the required resonator
Q's get into the million range.

I have in my junkbox a 20 KHz wide crystal filter with a center
frequency of 157 MHz used as a front end filter to improve VHF FM
receiver interference rejection from nearby paging transmitters. (Nearby
in both the geographical and frequency senses.)

Jack



Geoffrey Mackenzie-Kennedy wrote:

>
>> There are some many practical problems with the holder capacitance,
>> stray capacitance and the like that would make such a filter
>> challenging, even if someone were to deliver a box of 45 MHz crystals
>> with measured Qs of 2 million to my doorstep. And if  the box of
>> crystals arrive, to obtain frequency stability might require
>> stabilizing the filter assembly in a temperature controlled oven.
>>
>> The typical roofing filters at 45 MHz have a bandwidth of 20 KHz or
>> so. Thus the fractional bandwidth is 50 times larger and the Qx is
>> down into the 100K range, making these filters relatively easy to
>> realize.
>
> --------------------------------------------------------------------------
>
>
> An interesting 42.5 MHz filter design appeared several years ago using
> just four crystals in ladder configuration. The designer was not
> looking for narrow bandwidth nor good shape factor, but illustrating a
> "method". The bandwidth was 5 kHz, the shape factor was 4, stopband
> better than 80db and the response was symmetrical. In addition to the
> usual inductors across each crystal to take care of holder
> capacitance, as inspired by Zobel, two other other modifications were
> incorporated. (1) Parallel tuned circuits were placed at each end to
> prevent degeneration into a poor Cauer lowpass filter. (2) Parallel
> tuned circuits were used as coupling elements, presumably to tweak
> mesh frequencies. Insertion loss unknown, but a fair number of
> elements to compensate for temperature change.
>
> 73,
> Geoff
> GM4ESD
>
>
>
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N2EY]

In a message dated 8/12/06 8:03:20 AM Eastern Daylight Time,
[hidden email] writes:


> Hence, the resonator Q requirements for a 5 KHz filter at 40 MHz are not
> grossly different than for a 500 Hz filter at 4 MHz, which is quite
> achievable. But for a 400 Hz filter at 45 MHz, the required resonator
> Q's get into the million range.
>

Thanks, Jack - that's the answer I was looking for.

Most of us QRP/Elecraft types are going to want a rig with really good CW
selectivity. That means 500 Hz is the *wide* filter!  Which means a
single-conversion VHF-IF rx isn't practical - yet.

Of course the situation may change at some point.  For more than 20 years,
(1930s to mid 1950s?) "crystal filters" were pretty much limited to below about
500 kHz or so. Then in the late 1950s, high performance lattice filters for
the HF region appeared, and began to show up in amateur radio designs. ("What's
Wrong With Our Present Receivers?" QST, about 1957).

Those early HF xtal filters were rather expensive (the Hycon Eastern filters
in the above article were $44 each, which was a big pile of money in 1957!)
But of course prices (adjusted for inflation) came down over time.

73 de Jim, N2EY

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N8LP]

Speaking of cutoffs, I placed the parts orders for the 2nd run of LP-100
kits earlier this week. This is a limited run, similar to the initial
run, but I still have some slots left. You can read about the LP-100 at
www.telepostinc.com/lp100.html, with links to the QEX article, eHam.net
reviews, assembly manual, etc.

This is a perfect accessory for a QRP to QRO station. I offer free NIST
traceable calibration of the finished kits if desired (you pay only for
shipping).

73,
Larry N8LP
www.telepostinc.com



Jack Smith wrote:

> Just a short reminder that if you are planning to purchase a Z90 or
> Z91 panadapter kit, the deadline to drop me an E-mail message is
> Friday, August 18th.
>
> A few days after the 18th, I will order enough of the expensive
> volume-sensitive parts (enclosures, LCD, PCB) to meet the order
> requirements, to provide for two or three units for my use and to
> provide a small quantity for spare parts support. This means that if
> you miss the August 18th cut-off date, you will have to wait until the
> next batch build, which may be a rather long time.
>
> I can accept orders for small things, such as the interface boards,
> after the deadline date, up until I actually order those components.
>
> 73 de Jack K8ZOA
> www.cliftonlaboratories.com
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Geoffrey Mackenzie-Kennedy-2]

Jack Smith wrote:

> Hence, the resonator Q requirements for a 5 KHz filter at 40 MHz are not
> grossly different than for a 500 Hz filter at 4 MHz, which is quite
> achievable. But for a 400 Hz filter at 45 MHz, the required resonator Q's
> get into the million range.

-------------------------------------------------------------------

Quite right!  The first roofing filter that I built for trial used 12
inexpensive 36MHz crystals, not far from the IF to be used, with holder
capacitance compensation and strung out in a ladder. While it's 6db
bandwidth was a nominal 3 kHz and its shape factor was very good with
virtually a symmetrical response, its ability to handle large signals was
not good and a similar filter at the actual IF would have compromised the
overall receiver performance. For a reason that I do not yet fully
understand the problem appeared to centre around crystal #5, counting from
the input.

The 3kHz and 1.5kHz roofing filters in use each consists of three four pole
"crystal filter modules" each separated by very high IIP3 low noise
push-pull amplifiers running at very low gain, but power hungry. To reduce
the 6db bandwidth in the1.5kHz filter modules I have resorted to a "brute
force" method by adding shunt crystals (Dishal) in each module. With the
amplifiers the overall loss can be controlled, keeping in mind the overall
receiver performance requirements.

Much too expensive for a commercial rig, there must be better ways to beat
Q.

73,
Geoff
GM4ESD





 



_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

It wasn't just crystal filters that improved. The older methods of
computing component values (Image Parameter) was replaced by modern
network theory in the 1950's and '60's and LC filters became a lot
better performing as a result.

I don't see the widespread cheap availability of crystals with Q > 1
million as likely to emerge without a major demand and some considerable
advances in the materials available, as the present devices seem to do
the job required.

There's an interesting article "The Design and Performance of
Ultraprecise 2.5-mc Quartz Crystal Units" by A. W. Warner from the
September 1960 B.S.T.J. discussing crystals with a Q of 5 to 6 million.
You can read it at http://www.ieee-uffc.org/freqcontrol/warner.pdf

Now, if we could obtain a few dozen of those at 45 MHz, we would have
something indeed.


Jack


[hidden email] wrote:

> In a message dated 8/12/06 8:03:20 AM Eastern Daylight Time,
> [hidden email] writes:
>
>
>> Hence, the resonator Q requirements for a 5 KHz filter at 40 MHz are not
>> grossly different than for a 500 Hz filter at 4 MHz, which is quite
>> achievable. But for a 400 Hz filter at 45 MHz, the required resonator
>> Q's get into the million range.
>
>
> Thanks, Jack - that's the answer I was looking for.
>
> Most of us QRP/Elecraft types are going to want a rig with really good
> CW selectivity. That means 500 Hz is the *wide* filter!  Which means a
> single-conversion VHF-IF rx isn't practical - yet.
>
> Of course the situation may change at some point.  For more than 20
> years, (1930s to mid 1950s?) "crystal filters" were pretty much
> limited to below about 500 kHz or so. Then in the late 1950s, high
> performance lattice filters for the HF region appeared, and began to
> show up in amateur radio designs. ("What's Wrong With Our Present
> Receivers?" QST, about 1957).
>
> Those early HF xtal filters were rather expensive (the Hycon Eastern
> filters in the above article were $44 each, which was a big pile of
> money in 1957!) But of course prices (adjusted for inflation) came
> down over time.
>
> 73 de Jim, N2EY
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N2EY]

In a message dated 8/12/06 12:40:53 PM Eastern Daylight Time,
[hidden email] writes:


> It wasn't just crystal filters that improved. The older methods of
> computing component values (Image Parameter) was replaced by modern
> network theory in the 1950's and '60's and LC filters became a lot
> better performing as a result.

Excellent point!

Yet it was at that exact time that amateur designs were moving away from LC
filtering (such as the 50-60 kc. second IFs of receivers like the Hallicrafters
SX-88/S-76/SX-96/SX-100/SX-101) to HF crystal filters. The move to
transceivers and matched receiver/transmitter pairs (Heath SB line) may have had an
effect, too.

I'm not sure of the exact dates when it was first done, but by the mid 1960s
the use of computers to do circuit simulation and calculation was mainstream
in electronic design. Such design tools probably had an effect in that many
"paper designs" could be tried out in a short time, particularly for things like
filters..

>
> I don't see the widespread cheap availability of crystals with Q > 1
> million as likely to emerge without a major demand and some considerable
> advances in the materials available, as the present devices seem to do
> the job required.
>

Agreed. The main filter in the K2 uses selected microprocessor crystals and
some varicaps, yet gives very good CW performance and multiple bandwidths. By
comparison, one can easily spend half the cost of a basic K2 (or more) on a
couple of packaged CW filters for an HF IF. For VHF? I don't want to go there.  

> There's an interesting article "The Design and Performance of
> Ultraprecise 2.5-mc Quartz Crystal Units" by A. W. Warner from the
> September 1960 B.S.T.J. discussing crystals with a Q of 5 to 6 million.
> You can read it at http://www.ieee-uffc.org/freqcontrol/warner.pdf

Incredible stuff from almost a half century ago.

But to get that high Q, they went to pretty fancy methods, icnluding vacuum
mounting. However, they were probably using natural rather than synthetically
grown quartz.

The things I find most disheartening were the aging curve and the fact that
they were using the 5th overtone to get to 2.5 Mhz.
>
> Now, if we could obtain a few dozen of those at 45 MHz, we would have
> something indeed.
>

I can imagine the size and cost!

73 de Jim, N2EY
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

>
> Yet it was at that exact time that amateur designs were moving away from LC
> filtering (such as the 50-60 kc. second IFs of receivers like the Hallicrafters
> SX-88/S-76/SX-96/SX-100/SX-101) to HF crystal filters. The move to
> transceivers and matched receiver/transmitter pairs (Heath SB line) may have had an
> effect, too.
>  

It's interesting that Collins added the mechanical filter to the R390
(thus producing the R390A) as part of a 1955 cost reduction study. The
study report is floating around the Internet and I took a look at it
again tonight to refresh my recollection. The mechanical filter
substitution is discussed almost completely in terms of improved skirt
selectivity with little mention of cost savings. It's also interesting
to note that the mechanical filters made the receiver unusable for
direction finding as there was too much phase shift change with
frequency when compared with the R390's tuned transformer design.

Drake's first R4 used 50 KHz IF for selectivity but later receivers went
to crystal filters.

I imagine the move to crystal filters was driven by the desire to reduce
receiver size and to remove the need for skilled technicians to align
the IF stages. In the VHF and UHF world, Motorola stuck with potted LC
IF filters at 455 KHz (the famous "Permakay") well past the 1970's,
although GE went to crystal filters with the Master Pro (and maybe
before that; I'm a bit hazy on GE's gear between the ProgLine and
MasterPro.)
> I'm not sure of the exact dates when it was first done, but by the mid 1960s
> the use of computers to do circuit simulation and calculation was mainstream
> in electronic design. Such design tools probably had an effect in that many
> "paper designs" could be tried out in a short time, particularly for things like
> filters..
>
>  
I received my EE undergrad degree in 1968 and I recall using a
transmission line simulation program. Batch mode, submit your card deck
and get the answer back the next day. Zverev's classic book on filter
design was published in 1967 and its data tables are derived from
computer programs, but the book itself is silent on using computers to
design filters.
>
> Agreed. The main filter in the K2 uses selected microprocessor crystals and
> some varicaps, yet gives very good CW performance and multiple bandwidths. By
> comparison, one can easily spend half the cost of a basic K2 (or more) on a
> couple of packaged CW filters for an HF IF. For VHF? I don't want to go there.  
>  
I've been quite pleased with the filters as narrow as 200 Hz that I've
built using 8 MHz micro processor crystals. I have to grade them for
minimum Q and frequency matching, but the resulting filters are textbook
matches to the Gaussian prototype designs.

One of the two articles I've submitted  to the ARRL for consideration
for QEX covers some of my crystal filter work. Have yet to hear if it's
accepted, however.


Jack

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

Bob W7AVK wrote:
> Jack - Have been reading the mail and enjoyed the discussion.  Might
> also point out a reason for the mechanical filter in the 390A was
> Collins had the patent and Art was pushing their use.  I worked for
> Art a few years later and he was still activity pushing the filters
> for use in a data modems and other application.  It can be said work
> we did at that time [early 1960s] became the basis for the Rockwell
> Collins modem chip that was an industry standard in the 80-90s.
I'm shocked to think that Collins would suggest something like that ...
pushing the government to use their proprietary technology to increase
profits to Collins ... who would ever think that could happen.

>
> Also you might check the things about the phase shift across the
> mechanical filters pass band.  I'm sure its bad, but its been
> questioned that say that was only a CIA [remember them] cover story
> for a very black commo system of the day, parts of which are only now
> being discussed on the net.

I have a genuine Collins manufactured R390A here, and the equipment to
do group delay and phase shift  testing, but I don't like the though of
moving the receiver and steel cabinet from the second floor to the
basement shop. Ugh. Too much like work. I need to do it anyway, as the
receiver has been gradually developing a problem that causes the carrier
strength meter (my receiver has the original "glow in the dark" meters)
to show nearly full scale regardless of AGC setting or signal strength.
Probably a leaky cap in the AGC bus, but working on that receiver is not
my favorite activity.

I seem to recall reading that there might have been some early CDMA
systems on HF that were used by the CIA and that would require a wide
bandwidth receiver. However, I remember that as being well over 20 KHz
wide and maybe closer to 200 KHz. The idea is that they were low
probability of intercept signals as well as having spreading gain.

Jack

>
> Not sure, just my $0.02.  But maybe do some enjoyable surfing.
>
> 73  Bob  W7AVK
>
> Jack Smith wrote:
>>
>>>
>>> Yet it was at that exact time that amateur designs were moving away
>>> from LC filtering (such as the 50-60 kc. second IFs of receivers
>>> like the Hallicrafters SX-88/S-76/SX-96/SX-100/SX-101) to HF crystal
>>> filters. The move to transceivers and matched receiver/transmitter
>>> pairs (Heath SB line) may have had an effect, too.
>>>  
>>
>>
>> It's interesting that Collins added the mechanical filter to the R390
>> (thus producing the R390A) as part of a 1955 cost reduction study.
>> The study report is floating around the Internet and I took a look at
>> it again tonight to refresh my recollection. The mechanical filter
>> substitution is discussed almost completely in terms of improved
>> skirt selectivity with little mention of cost savings. It's also
>> interesting to note that the mechanical filters made the receiver
>> unusable for direction finding as there was too much phase shift
>> change with frequency when compared with the R390's tuned transformer
>> design.
>>
>> Drake's first R4 used 50 KHz IF for selectivity but later receivers
>> went to crystal filters.
>>
>> I imagine the move to crystal filters was driven by the desire to
>> reduce receiver size and to remove the need for skilled technicians
>> to align the IF stages. In the VHF and UHF world, Motorola stuck with
>> potted LC IF filters at 455 KHz (the famous "Permakay") well past the
>> 1970's, although GE went to crystal filters with the Master Pro (and
>> maybe before that; I'm a bit hazy on GE's gear between the ProgLine
>> and MasterPro.)
>>
>>> I'm not sure of the exact dates when it was first done, but by the
>>> mid 1960s the use of computers to do circuit simulation and
>>> calculation was mainstream in electronic design. Such design tools
>>> probably had an effect in that many "paper designs" could be tried
>>> out in a short time, particularly for things like filters..
>>>  
>>
>> I received my EE undergrad degree in 1968 and I recall using a
>> transmission line simulation program. Batch mode, submit your card
>> deck and get the answer back the next day. Zverev's classic book on
>> filter design was published in 1967 and its data tables are derived
>> from computer programs, but the book itself is silent on using
>> computers to design filters.
>>
>>>
>>> Agreed. The main filter in the K2 uses selected microprocessor
>>> crystals and some varicaps, yet gives very good CW performance and
>>> multiple bandwidths. By comparison, one can easily spend half the
>>> cost of a basic K2 (or more) on a couple of packaged CW filters for
>>> an HF IF. For VHF? I don't want to go there.    
>>
>> I've been quite pleased with the filters as narrow as 200 Hz that
>> I've built using 8 MHz micro processor crystals. I have to grade them
>> for minimum Q and frequency matching, but the resulting filters are
>> textbook matches to the Gaussian prototype designs.
>>
>> One of the two articles I've submitted  to the ARRL for consideration
>> for QEX covers some of my crystal filter work. Have yet to hear if
>> it's accepted, however.
>>
>>
>> Jack
> .
>
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N2EY]

In a message dated 8/12/06 8:46:40 PM Eastern Daylight Time,
[hidden email] writes:


>
> It's interesting that Collins added the mechanical filter to the R390
> (thus producing the R390A) as part of a 1955 cost reduction study. The
> study report is floating around the Internet and I took a look at it
> again tonight to refresh my recollection. The mechanical filter
> substitution is discussed almost completely in terms of improved skirt
> selectivity with little mention of cost savings.

I think there were other changes, too. IIRC, the 390A is in some ways simpler
than the 390.

It's also interesting
>
> to note that the mechanical filters made the receiver unusable for
> direction finding as there was too much phase shift change with
> frequency when compared with the R390's tuned transformer design.
>

The story goes like this:

Back during the Cold War, No Such Agency had the idea for a secure comm
system which eventually became known as F9C in FCC mode labeling of the time.
They wanted to use R-390As for the system, but the phase shift through the
mechanical filters was a problem. So they had a version of the R-390A made with
R-390 type LC IF strips. This variant was designated R-725.

To cover their tracks about the reason for the variant, a cover story about
an electronically-steered RDF system was invented. The cover story was so
convincing that the "other folks" apparently never became aware of, nor penetrated,
the F9C system. Eventually the F9C system was replaced by newer technology,
which is why we know the story now.

It is my understanding that, long after the F9C system was in operation, an
electronically steered RDF system using the receivers *was* developed!

All ancient history now.

> Drake's first R4 used 50 KHz IF for selectivity but later receivers went
> to crystal filters.
>

Actually the R4, R4A, and R4B all used LC filtering at 50 kHz for selectivity
and passband tuning. Only the R4C used all-crystal filtering.

> I imagine the move to crystal filters was driven by the desire to reduce
> receiver size and to remove the need for skilled technicians to align
> the IF stages.

I think the main reason was the amateur HF SSB transceiver, which began
replacing 'separates' in the late 1950s and early 1960s. While the first ones
(Cosmophone 35, KWM-1 & -2) used 455 kc mechanical filters, other manufacturers
went to crystal filters in the HF range, probably to both save money and avoid
being dependent on Collins.

IMHO, the amateur HF SSB transceiver is what really made SSB popular with
hams. By the early 1960s, a ham could buy a 100-watt-class SSB xcvr for about the
price of a really good receiver. No critical zero beating, and the whole
works was much smaller and lighter than the common desk-crusher AM rigs.  


In the VHF and UHF world, Motorola stuck with potted LC
>
> IF filters at 455 KHz (the famous "Permakay") well past the 1970's,
> although GE went to crystal filters with the Master Pro (and maybe
> before that; I'm a bit hazy on GE's gear between the ProgLine and
> MasterPro.)

Could it be that obtaining a suitable FM-bandwidth filter was easier/less
expensive (for Motorola, anyway) with LC circuits?

> > I'm not sure of the exact dates when it was first done, but by the mid
> 1960s
> > the use of computers to do circuit simulation and calculation was
> mainstream
> > in electronic design. Such design tools probably had an effect in that
> many
> > "paper designs" could be tried out in a short time, particularly for
> things like
> > filters..
> >
> >  
> I received my EE undergrad degree in 1968 and I recall using a
> transmission line simulation program. Batch mode, submit your card deck
> and get the answer back the next day. Zverev's classic book on filter
> design was published in 1967 and its data tables are derived from
> computer programs, but the book itself is silent on using computers to
> design filters.
>

Well, I graduated EE school in 1976, and by then programs like SPICE were
part of the curriculum. Still batch processing, though, but the whole idea was
neither new nor revolutionary then.

>
> > Agreed. The main filter in the K2 uses selected microprocessor crystals
> and
> > some varicaps, yet gives very good CW performance and multiple bandwidths.
> By
> > comparison, one can easily spend half the cost of a basic K2 (or more) on
> a
> > couple of packaged CW filters for an HF IF. For VHF? I don't want to go the
> re.  
> >  
> I've been quite pleased with the filters as narrow as 200 Hz that I've
> built using 8 MHz micro processor crystals.

My point exactly.

I have to grade them for
>
> minimum Q and frequency matching, but the resulting filters are textbook
> matches to the Gaussian prototype designs.
>

It is my understanding that the crystals in Elecraft products are graded in
similar fashion. I think they are selected/matched for a number of different
parameters.

Sometimes I wonder how many "microprocessor crystals" in the HF range
actually wind up working with microprocessors...

> One of the two articles I've submitted  to the ARRL for consideration
> for QEX covers some of my crystal filter work. Have yet to hear if it's
> accepted, however.
>
>

I hope they are accepted.

73 es tnx de Jim, N2EY

> Jack
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jack Smith-6]

> I think there were other changes, too. IIRC, the 390A is in some ways simpler
> than the 390.
>  
If you don't have it, I'll send you a PDF of the "Cost Reduction Study"
report Collins did that lead to the R390A.

> The story goes like this:
>
> Back during the Cold War, No Such Agency had the idea for a secure comm
> system which eventually became known as F9C in FCC mode labeling of the time.
> They wanted to use R-390As for the system, but the phase shift through the
> mechanical filters was a problem. So they had a version of the R-390A made with
> R-390 type LC IF strips. This variant was designated R-725.
>
> To cover their tracks about the reason for the variant, a cover story about
> an electronically-steered RDF system was invented. The cover story was so
> convincing that the "other folks" apparently never became aware of, nor penetrated,
> the F9C system. Eventually the F9C system was replaced by newer technology,
> which is why we know the story now.
>
> It is my understanding that, long after the F9C system was in operation, an
> electronically steered RDF system using the receivers *was* developed!
>
> All ancient history now.
>
>  

I worked for the FCC as an engineer for several years after EE graduate
school and had an opportunity to visit a monitoring station. As I
recall, they used 51J4's for general listening and Racal 17 (US model
numbers RA117 and RA6117) for DF use with the Wullenwebber array. The
RA17 series receiver used LC filters for wider bandwidths and a crystal
lattice filter for the narrower bandwidths. The military used the same
Wullenwebber antenna system (elephant cages) and I had heard (but never
seen one in person) that they used R390's.
>> Drake's first R4 used 50 KHz IF for selectivity but later receivers went
>> to crystal filters.
>>
>>    
>
> Actually the R4, R4A, and R4B all used LC filtering at 50 kHz for selectivity
> and passband tuning. Only the R4C used all-crystal filtering.
>
>  
My first Drake was a R4C.

>> I imagine the move to crystal filters was driven by the desire to reduce
>> receiver size and to remove the need for skilled technicians to align
>> the IF stages.
>>    
>
> I think the main reason was the amateur HF SSB transceiver, which began
> replacing 'separates' in the late 1950s and early 1960s. While the first ones
> (Cosmophone 35, KWM-1 & -2) used 455 kc mechanical filters, other manufacturers
> went to crystal filters in the HF range, probably to both save money and avoid
> being dependent on Collins.
>
> IMHO, the amateur HF SSB transceiver is what really made SSB popular with
> hams. By the early 1960s, a ham could buy a 100-watt-class SSB xcvr for about the
> price of a really good receiver. No critical zero beating, and the whole
> works was much smaller and lighter than the common desk-crusher AM rigs.  
>
>
> In the VHF and UHF world, Motorola stuck with potted LC
>  
>> IF filters at 455 KHz (the famous "Permakay") well past the 1970's,
>> although GE went to crystal filters with the Master Pro (and maybe
>> before that; I'm a bit hazy on GE's gear between the ProgLine and
>> MasterPro.)
>>    
>
> Could it be that obtaining a suitable FM-bandwidth filter was easier/less
> expensive (for Motorola, anyway) with LC circuits?
>  

The design problem with FM filters is both bandwidth and ensuring group
delay specs are met, as otherwise audio distortion is an issue. My
junkbox also has a wideband 70 MHz center frequency IF filter from a
Western Electric analog microwave system. It has a bandwidth of 10 or 20
MHz and excellent group delay characteristics, which, of course, were
essential for a microwave system carrying hundreds of multiplexed analog
SSB channels.

>  
>>> I'm not sure of the exact dates when it was first done, but by the mid
>>>      
>> 1960s
>>    
>>> the use of computers to do circuit simulation and calculation was
>>>      
>> mainstream
>>    
>>> in electronic design. Such design tools probably had an effect in that
>>>      
>> many
>>    
>>> "paper designs" could be tried out in a short time, particularly for
>>>      
>> things like
>>    
>>> filters..
>>>
>>>  
>>>      
>> I received my EE undergrad degree in 1968 and I recall using a
>> transmission line simulation program. Batch mode, submit your card deck
>> and get the answer back the next day. Zverev's classic book on filter
>> design was published in 1967 and its data tables are derived from
>> computer programs, but the book itself is silent on using computers to
>> design filters.
>>
>>    
>
> Well, I graduated EE school in 1976, and by then programs like SPICE were
> part of the curriculum. Still batch processing, though, but the whole idea was
> neither new nor revolutionary then.
>  

In my senior year (1968) the engineering department was bringing on line
a remote access time share system using IBM-selectwriters (IBM golf-ball
typewriter type terminals) but it was highly experimental and was down
more than it was up. My course in computer programming (Numerical
Methods) was oriented towards solving physics problems.

>>> Agreed. The main filter in the K2 uses selected microprocessor crystals
>>>      
>> and
>>    
>>> some varicaps, yet gives very good CW performance and multiple bandwidths.
>>>      
>> By
>>    
>>> comparison, one can easily spend half the cost of a basic K2 (or more) on
>>>      
>> a
>>    
>>> couple of packaged CW filters for an HF IF. For VHF? I don't want to go the
>>>      
>> re.  
>>    
>>>  
>>>      
>> I've been quite pleased with the filters as narrow as 200 Hz that I've
>> built using 8 MHz micro processor crystals.
>>    
>
> My point exactly.
>
> I have to grade them for
>  
>> minimum Q and frequency matching, but the resulting filters are textbook
>> matches to the Gaussian prototype designs.
>>
>>    
>
> It is my understanding that the crystals in Elecraft products are graded in
> similar fashion. I think they are selected/matched for a number of different
> parameters.
>
> Sometimes I wonder how many "microprocessor crystals" in the HF range
> actually wind up working with microprocessors...
>
>  
>> One of the two articles I've submitted  to the ARRL for consideration
>> for QEX covers some of my crystal filter work. Have yet to hear if it's
>> accepted, however.
>>
>>
>>    
>
> I hope they are accepted.
>
> 73 es tnx de Jim, N2EY
>
>
>
>  
>> Jack
>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft   
>>
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>    
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft   
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>  

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N8LP]

That's funny. I have never heard that phrase used to describe a
Wullenwebber array, but it's an apt description.

Larry N8LP



Jack Smith wrote:
>
> The military used the same Wullenwebber antenna system (elephant
> cages) and I had heard (but never seen one in person) that they used
> R390's.
>
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[N2EY]

In a message dated 8/13/06 7:56:46 AM Eastern Daylight Time,
[hidden email] writes:


> If you don't have it, I'll send you a PDF of the "Cost Reduction Study"
> report Collins did that lead to the R390A.

I'd really like a copy - thanks! I think others would too.
>
> > The story goes like this:
> >
> > Back during the Cold War, No Such Agency

....

> >
> > It is my understanding that, long after the F9C system was in operation,
> an
> > electronically steered RDF system using the receivers *was* developed!
> >
> > All ancient history now.
> >  
> I worked for the FCC as an engineer for several years after EE graduate
> school and had an opportunity to visit a monitoring station. As I
> recall, they used 51J4's for general listening and Racal 17 (US model
> numbers RA117 and RA6117) for DF use with the Wullenwebber array.

I don't know if the R-390/R-725 were used with the Wullenwebber system or
something else. Either way, it makes sense that the phase characteristics of the
mechanical filters were a problem.

The
>
> RA17 series receiver used LC filters for wider bandwidths and a crystal
> lattice filter for the narrower bandwidths. The military used the same
> Wullenwebber antenna system (elephant cages) and I had heard (but never
> seen one in person) that they used R390's.

Or R-725s, which would look very similar.

> >> Drake's first R4 used 50 KHz IF for selectivity but later receivers went
>
> >> to crystal filters.
>  
> > Actually the R4, R4A, and R4B all used LC filtering at 50 kHz for
> selectivity
> > and passband tuning. Only the R4C used all-crystal filtering.
>    
> My first Drake was a R4C.

A family of HF ham receivers that bridged the change from low-frequency LC
selectivity to HF crystal filters. R-4B and the Drake 2-B/2-C family may have
been the last manufactured ham rxs to use LC IF filtering for multiple-bandwidth
selectivity.

> >
> > Could it be that obtaining a suitable FM-bandwidth filter was easier/less
> > expensive (for Motorola, anyway) with LC circuits?
> >  
> The design problem with FM filters is both bandwidth and ensuring group
> delay specs are met, as otherwise audio distortion is an issue. My
> junkbox also has a wideband 70 MHz center frequency IF filter from a
> Western Electric analog microwave system. It has a bandwidth of 10 or 20
> MHz and excellent group delay characteristics, which, of course, were
> essential for a microwave system carrying hundreds of multiplexed analog
> SSB channels.
>

By contrast, IIRC, RCA made some mechanical filters for receivers they
provided to the military in the 1950s. From what I read, they were just different
enough from Collins design that they avoided patent infringement. They were also
(allegedly) quite fragile.

  > > Well, I graduated EE school in 1976, and by then programs like SPICE

> were
> > part of the curriculum. Still batch processing, though, but the whole idea
> was
> > neither new nor revolutionary then.
> >  
> In my senior year (1968) the engineering department was bringing on line
> a remote access time share system using IBM-selectwriters (IBM golf-ball
> typewriter type terminals) but it was highly experimental and was down
> more than it was up. My course in computer programming (Numerical
> Methods) was oriented towards solving physics problems.

Perhaps my timeline was a bit too soon. By the time I was in EE school (fall
of 1972), SPICE and other circuit-simulation-by-computer stuff was common at
the school I went to. Perhaps it was a lot more recent than I realized at the
time.

73 de Jim, N2EY
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Bob W7AVK]

Good Morning - You are correct, RCA made some mechanical filters before
Collins.   But the Collins patent and improvement was not the filter but
the unique disk shape and material that made them self temperature
compensating so they were mil spec.  It was the first that opened the door.

73  Bob  W7AVK

[hidden email] wrote:

> In a message dated 8/13/06 7:56:46 AM Eastern Daylight Time,
> [hidden email] writes:
>
>
>
>>If you don't have it, I'll send you a PDF of the "Cost Reduction Study"
>>report Collins did that lead to the R390A.
>
>
> I'd really like a copy - thanks! I think others would too.
>
>>>The story goes like this:
>>>
>>>Back during the Cold War, No Such Agency
>
>
> ....
>
>>>It is my understanding that, long after the F9C system was in operation,
>>
>>an
>>
>>>electronically steered RDF system using the receivers *was* developed!
>>>
>>>All ancient history now.
>>>  
>>
>>I worked for the FCC as an engineer for several years after EE graduate
>>school and had an opportunity to visit a monitoring station. As I
>>recall, they used 51J4's for general listening and Racal 17 (US model
>>numbers RA117 and RA6117) for DF use with the Wullenwebber array.
>
>
> I don't know if the R-390/R-725 were used with the Wullenwebber system or
> something else. Either way, it makes sense that the phase characteristics of the
> mechanical filters were a problem.
>
> The
>
>>RA17 series receiver used LC filters for wider bandwidths and a crystal
>>lattice filter for the narrower bandwidths. The military used the same
>>Wullenwebber antenna system (elephant cages) and I had heard (but never
>>seen one in person) that they used R390's.
>
>
> Or R-725s, which would look very similar.
>
>
>>>>Drake's first R4 used 50 KHz IF for selectivity but later receivers went
>>
>>>>to crystal filters.
>>
>>
>>
>>>Actually the R4, R4A, and R4B all used LC filtering at 50 kHz for
>>
>>selectivity
>>
>>>and passband tuning. Only the R4C used all-crystal filtering.
>>
>>  
>>My first Drake was a R4C.
>
>
> A family of HF ham receivers that bridged the change from low-frequency LC
> selectivity to HF crystal filters. R-4B and the Drake 2-B/2-C family may have
> been the last manufactured ham rxs to use LC IF filtering for multiple-bandwidth
> selectivity.
>
>>>Could it be that obtaining a suitable FM-bandwidth filter was easier/less
>>>expensive (for Motorola, anyway) with LC circuits?
>>>  
>>
>>The design problem with FM filters is both bandwidth and ensuring group
>>delay specs are met, as otherwise audio distortion is an issue. My
>>junkbox also has a wideband 70 MHz center frequency IF filter from a
>>Western Electric analog microwave system. It has a bandwidth of 10 or 20
>>MHz and excellent group delay characteristics, which, of course, were
>>essential for a microwave system carrying hundreds of multiplexed analog
>>SSB channels.
>>
>
>
> By contrast, IIRC, RCA made some mechanical filters for receivers they
> provided to the military in the 1950s. From what I read, they were just different
> enough from Collins design that they avoided patent infringement. They were also
> (allegedly) quite fragile.
>
>   > > Well, I graduated EE school in 1976, and by then programs like SPICE
>
>>were
>>
>>>part of the curriculum. Still batch processing, though, but the whole idea
>>
>>was
>>
>>>neither new nor revolutionary then.
>>>  
>>
>>In my senior year (1968) the engineering department was bringing on line
>>a remote access time share system using IBM-selectwriters (IBM golf-ball
>>typewriter type terminals) but it was highly experimental and was down
>>more than it was up. My course in computer programming (Numerical
>>Methods) was oriented towards solving physics problems.
>
>
> Perhaps my timeline was a bit too soon. By the time I was in EE school (fall
> of 1972), SPICE and other circuit-simulation-by-computer stuff was common at
> the school I went to. Perhaps it was a lot more recent than I realized at the
> time.
>
> 73 de Jim, N2EY
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft   
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Geoffrey Mackenzie-Kennedy-2]

[hidden email] wrote on Sunday, August 13, 2006 at 5:32 PM


> By contrast, IIRC, RCA made some mechanical filters for receivers they
> provided to the military in the 1950s. From what I read, they were just
> different
> enough from Collins design that they avoided patent infringement. They
> were also
> (allegedly) quite fragile.


The alleged fragility of the RCA mechanical filters might well have been a
story put out by the competition. I was involved at that time in the design
of the 100w variant of RCA's SSB-1 which used RCA's mechanical filters, as
did at least one of RCA's higher powered ISB rigs. I cannot recall any
feedback from the field related to the filters.

73,
Geoff
GM4ESD



_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[k6dgw]

How these threads do morph!  I don't know about RCA MF's, but I can
attest to the extreme non-fragility of the Collins variety (and in fact
"everything Collins").

In the mid-60's, while in the USAF (1Lt), I commanded an airborne team
whose missions were to put mobile, hardened TACANS on various mountain
tops in undisclosed locations for 10-15 days.  After getting down, we
got our equipment out of the C-130 using LAPES (Low Altitude Parachute
Extraction System).  The gear was mounted on shock pallets, the A/C made
a low pass and, with a tail-hook apparatus, snagged a shock cable we had
erected on flimsy poles, and flew out from under the pallets.  Snap
opening cargo chutes "landed the pallets," as the system description
quaintly said.  Despite all the shock protection, "landed" was really
stretching the term, even for the guvmint.

The pallets always contained two KWM-2A's packed in aluminum foam-lined
cases which we used to communicate with our FOHQ south of the 17th who
coordinated the CH-3's to come pick us up when we'd run out of JP4 for
the generators.  The tubes were packed separately, but other than that,
the 2A's were stock, ready to transmit.  We did 24 of these missions and
I lost four troops, but we lost zero out of 48 -2A's.  Collins also
manufactured our A/G radios (can't remember their nomenclature at the
moment), and we never lost one of those either.

Unfortunately, our missions ended by lighting off thermite on the pile
of equipment ... burning up 48 perfectly serviceable, beautiful KWM-2A's
was really really hard for a ham, and I wondered if my ham colleagues
would ever forgive me.

I used an S3-line for years, and while I don't have it any more to do an
A/B test, based on my memory (a bit leaky these days), I think the K2 IF
filters will easily stand up to the mech filters ... and, unlike the
MF's, I can tailor the K2 filters as I wish.

I think someone suggested that the move from AM to SSB was driven by the
superior filtering that became available at the same time (please
forgive me if I got that wrong).  Personally, I think it was VOX.

Re R390A's:  The Wullenweber array and station at Clark AB in the
Philippines, operated by the ATDE ("Agency That Doesn't Exist"), used
390A's.  I wasn't permitted to know for what.

Fred K6DGW
Auburn CA CM98lw
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com