Price Comparison and Comment

[Bill W4ZV]

W5EWA:
 >but now someone says that we DON'T need them all.

         Definitely not...unless we have more money than
sense.  You need only ONE per major mode, which will
cover the widest bandwidth you ever expect to use in
that mode.  For example:

CW - 500 or 400.  250 and 200 are definite overkill
IMHO and not necessary in addition to narrow DSP BWs.
The reason is that IMD/BDR spurious issues at <500 Hz
will be far overridden by other issues such as phase noise,
key clicks, etc that come from the transmitted signals.
There is no point in making a receiver many dB better
than the environment in which it must live!  No matter
how good a receiver is it cannot eliminate transmitter
defects (maybe Flex's SDR-X can but that remains to be
proven).

SSB - 2.7 kHz unless you want ESSB (not sure how high
that goes these days but IMHO we should be trying to
minimize communications bandwidths rather than playing
broadcast disc jockey (my personal opinion!).  Those
folks should go to 29 MHz FM if they want to do that.

AM - 6 kHz

FM - 15 kHz

         In fact you may not need ANY filters beyond
the 2.7 kHz stock filter unless you expect to have lots
of very close spaced S9+30 dB signals on CW (e.g. huge
low-band pileups or in contests).  The 2.7k should be
perfectly adequate for nearly any situation on SSB,
although it wouldn't surprise me to see someone offer
1.8 kHz, mainly for contesters.

         A roofing filter's purpose is simply to minimize
spurious artifacts from being created *inside* the RX
by external signals.  It does NOT create the ultimate
selectivity (which is determined by the DSP filter at
the 2nd IF).  Please read the last sentence again!
Here's a simple summary:


Antenna > roofing filter > DSP filter > ear.

...roofing filter prevents very strong signals from
creating spurious (i.e. *NOT REAL*) signals which
will then appear inside the DSP.

...DSP filters provide the ultimate selectivity (i.e.
separating the *REAL* signals from each other).


         The number of poles (i.e. shape factor of the
filter) can affect IMD/BDR issues inside the RX.  For
this reason hopefully Elecraft will provide actual
IMD/BDR measurements with each option to help answer
the following questions:

1.  Is the optional 8-pole 2.8 kHz better than the
stock 5-pole 2.7 kHz (by "better" I mean resulting
in better IMD/BDR performance which is the primary
purpose of a roofing filter).

2.  Is the 5-pole 500 Hz better than the 8-pole 400 Hz?

3.  Is the 8-pole 250 Hz better than the 5-pole 200 Hz?
(academic to me since I don't feel either is necessary
...see comment above re TX key clicks, phase noise, etc).

         The variable BW filters are interesting but
I would not consider them until we have some actual
results for IMD/BDR.  They are NOT providing ultimate
selectivity as they do in the case of the K2, which
seems to be confusing many folks.

                                 73,  Bill  W4ZV




_______________________________________________
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

[Don Wilhelm-3]

Bill,

All of what you say is true *EXCEPT* for one item - and that is the AGC.

The hardware AGC is developed before any DSP processing, so when there
are strong signals inside the roofing filter passband, they will
activate the AGC and reduce the receiver sensitivity.  If you have the
DSP cranked down to a narrow bandwidth, you may not even hear the
offending strong signal because it is outside the DSP bandwidth but
still inside the roofing filter bandwidth.

BTW, this can happen on the K2 (and many other receivers) if a wide
bandwidth is selected and the DSP is used to reduce the signal to only
the desired one.

That is not really tough to deal with if you are already listening to an
S-9 signal even though an S-9 +30 signal comes on - the S-9 signal will
be reduced to the equivalent of an S-4 or S-5 signal and that can easily
be solid copy (because other signals in the DSP passband are similarly
reduced).

Now, if the signal you are trying to copy is an S-1 or S-2 level and an
S-9 signal comes into the roofing filter passband (again it may be out
of the DSP passband and will not be heard), the receiver gain will be
reduced and you will no longer hear the S-1/S-2 signal - just like QSB,
but it is QSB induced in the receiver, not due to propagation effects.

I will have at least one narrow filter available in my K3.  Bill, you
were correct that a filter is needed for each major mode, but the
filters that any one person needs will be determined by their operating
habits, and not based on the 'average'.  For ragchewing and  casual
contacts, even the wide 2.7 kHz filter may be all that is needed, but
for serious CW, QRP, contesting or DX chasing, an array of filters will
be needed - just how many will depend on the operator's desires to
reduce QRM and the amount available in the ham radio budget.

73,
Don W3FPR

Bill Tippett wrote:

> W5EWA:
>  >but now someone says that we DON'T need them all.
>
>         Definitely not...unless we have more money than
> sense.  You need only ONE per major mode, which will
> cover the widest bandwidth you ever expect to use in
> that mode.  For example:
>
> CW - 500 or 400.  250 and 200 are definite overkill
> IMHO and not necessary in addition to narrow DSP BWs.
> The reason is that IMD/BDR spurious issues at <500 Hz
> will be far overridden by other issues such as phase noise,
> key clicks, etc that come from the transmitted signals.
> There is no point in making a receiver many dB better
> than the environment in which it must live!  No matter
> how good a receiver is it cannot eliminate transmitter
> defects (maybe Flex's SDR-X can but that remains to be
> proven).
>
> SSB - 2.7 kHz unless you want ESSB (not sure how high
> that goes these days but IMHO we should be trying to
> minimize communications bandwidths rather than playing
> broadcast disc jockey (my personal opinion!).  Those
> folks should go to 29 MHz FM if they want to do that.
>
> AM - 6 kHz
>
> FM - 15 kHz
>
>         In fact you may not need ANY filters beyond
> the 2.7 kHz stock filter unless you expect to have lots
> of very close spaced S9+30 dB signals on CW (e.g. huge
> low-band pileups or in contests).  The 2.7k should be
> perfectly adequate for nearly any situation on SSB,
> although it wouldn't surprise me to see someone offer
> 1.8 kHz, mainly for contesters.
>
>         A roofing filter's purpose is simply to minimize
> spurious artifacts from being created *inside* the RX
> by external signals.  It does NOT create the ultimate
> selectivity (which is determined by the DSP filter at
> the 2nd IF).  Please read the last sentence again!
> Here's a simple summary:
>
>
> Antenna > roofing filter > DSP filter > ear.
>
> ...roofing filter prevents very strong signals from
> creating spurious (i.e. *NOT REAL*) signals which
> will then appear inside the DSP.
>
> ...DSP filters provide the ultimate selectivity (i.e.
> separating the *REAL* signals from each other).
>
>
>         The number of poles (i.e. shape factor of the
> filter) can affect IMD/BDR issues inside the RX.  For
> this reason hopefully Elecraft will provide actual
> IMD/BDR measurements with each option to help answer
> the following questions:
>
> 1.  Is the optional 8-pole 2.8 kHz better than the
> stock 5-pole 2.7 kHz (by "better" I mean resulting
> in better IMD/BDR performance which is the primary
> purpose of a roofing filter).
>
> 2.  Is the 5-pole 500 Hz better than the 8-pole 400 Hz?
>
> 3.  Is the 8-pole 250 Hz better than the 5-pole 200 Hz?
> (academic to me since I don't feel either is necessary
> ...see comment above re TX key clicks, phase noise, etc).
>
>         The variable BW filters are interesting but
> I would not consider them until we have some actual
> results for IMD/BDR.  They are NOT providing ultimate
> selectivity as they do in the case of the K2, which
> seems to be confusing many folks.
>
>                                 73,  Bill  W4ZV

_______________________________________________
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

[Bill W4ZV]

At 07:34 PM 5/4/07, Don Wilhelm wrote:

>All of what you say is true *EXCEPT* for one item - and that is the AGC.

         Don you are absolutely correct.  The reason
I never considered it is that I have never experienced it
with my Orion.  I seldom operate with strong signals
spaced much closer than 500 Hz.  The most severe
case of this may be in the CQ 160 CW Contest where
it's not uncommon for S9+20 to 30 signals to be spaced
every 500 Hz.  With typical key click bandwidths, very
few people will try to get closer than 500 Hz.  Given
500 Hz signal spacing and given a 500 Hz BW filter,
the filter easily knocks them down to a reasonable
level, since the filter BW is +/- 250 Hz and the signals
are +/- 500 Hz.

         Orion uses a two-stage AGC system, one is
analog and ahead of the DSP.  It has has the main
function of preventing over-driving the DSP stage.

"ADC overload can never be allowed to occur because when that
happens, signals are irrevocably corrupted. Signals that are larger
than the full-scale range of the ADC must force reduction of gain in
the analog section of the receiver. So both analog and digital AGCs
are used in the Orion. Resort to analog AGC only need be made when
signals inside the roofing bandwidth exceed about S-9 plus 30 dB. At
that point, sensitivity is reduced but what we are discovering is
that phase-noise performance-- as determined by reciprocal-mixing
measurements-- already limits what you can hear. So performance is
phase-noise limited and not DSP limited. Even so, the Orion gives you
the option of kicking in a crystal filter, preventing movement of the
analog AGC and the sensitivity reduction described above."

http://www.doug-smith.net/orion.htm

         As stated, this analog AGC does not activate
until signals reach the S9+35 range.  The second AGC is
digital and internal to the DSP (which works very well).

"As the resolution and speed of ADC hardware improve, digital radio
receivers become less dependent on analog AGC to meet dynamic-range
requirements. State-of-the-art 24-bit IF-DSP converters, such as
those used in the Ten-Tec Orion, produce about 100 dB of dynamic
range. That means a receiver can handle signals from the noise floor
to almost 40 dB over S9 without analog AGC. Above that level, analog
AGC is still necessary to maintain the linearity of analog circuits
and to prevent overload in the ADC hardware."

http://www.doug-smith.net/dspdynamics.htm

         I haven't seen much about the K3 AGC but I
hope it uses a similar same technique as Orion.  I have
NEVER heard any AGC pumping in Orion, even under
severe situations like the CQ 160 CW Contest which
I consider the ultimate test for any receiver.  I guess
that's why it did not occur to me to mention it.  Maybe
one of the Elecraft folk will tell us more abour the K3
AGC.

                         73,  Bill  W4ZV



_______________________________________________
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

[Don Wilhelm-3]

Bill,

I did ask Wayne about the AGC (with respect to the roofing filter
selection) and he indicated that the AGC was developed in hardware
before the A/D conversion and there is additional AGC action created in
the DSP.  As I understand it, it is similar to that which you describe
in the Orion.

Yes, from a receiver performance standpoint, only the A/D overload
problem counts (and it is critical), but from an operating (AGC pumping)
standpoint, there can be undesired performance in the presence of strong
signals that pass through the roofing filter even though they are
filtered out by the DSP because they will reduce the overall gain of the
receiver.  Quite apart from the receiver specs, it does show up during
operation and the AGC pumping can be a real problem for weak signal
reception regardless of the total dynamic range of the receiver.

We both await the real details on the K3 AGC (and other things too).

73,
Don W3FPR

Bill Tippett wrote:

> At 07:34 PM 5/4/07, Don Wilhelm wrote:
>
>> All of what you say is true *EXCEPT* for one item - and that is the AGC.
>
>         Don you are absolutely correct.  The reason
> I never considered it is that I have never experienced it
> with my Orion.  I seldom operate with strong signals
> spaced much closer than 500 Hz.  The most severe
> case of this may be in the CQ 160 CW Contest where
> it's not uncommon for S9+20 to 30 signals to be spaced
> every 500 Hz.  With typical key click bandwidths, very
> few people will try to get closer than 500 Hz.  Given
> 500 Hz signal spacing and given a 500 Hz BW filter,
> the filter easily knocks them down to a reasonable
> level, since the filter BW is +/- 250 Hz and the signals
> are +/- 500 Hz.
>
>         Orion uses a two-stage AGC system, one is
> analog and ahead of the DSP.  It has has the main
> function of preventing over-driving the DSP stage.
>
> "ADC overload can never be allowed to occur because when that happens,
> signals are irrevocably corrupted. Signals that are larger than the
> full-scale range of the ADC must force reduction of gain in the analog
> section of the receiver. So both analog and digital AGCs are used in the
> Orion. Resort to analog AGC only need be made when signals inside the
> roofing bandwidth exceed about S-9 plus 30 dB. At that point,
> sensitivity is reduced but what we are discovering is that phase-noise
> performance-- as determined by reciprocal-mixing measurements-- already
> limits what you can hear. So performance is phase-noise limited and not
> DSP limited. Even so, the Orion gives you the option of kicking in a
> crystal filter, preventing movement of the analog AGC and the
> sensitivity reduction described above."
>
> http://www.doug-smith.net/orion.htm
>
>         As stated, this analog AGC does not activate
> until signals reach the S9+35 range.  The second AGC is
> digital and internal to the DSP (which works very well).
>
> "As the resolution and speed of ADC hardware improve, digital radio
> receivers become less dependent on analog AGC to meet dynamic-range
> requirements. State-of-the-art 24-bit IF-DSP converters, such as those
> used in the Ten-Tec Orion, produce about 100 dB of dynamic range. That
> means a receiver can handle signals from the noise floor to almost 40 dB
> over S9 without analog AGC. Above that level, analog AGC is still
> necessary to maintain the linearity of analog circuits and to prevent
> overload in the ADC hardware."
>
> http://www.doug-smith.net/dspdynamics.htm
>
>         I haven't seen much about the K3 AGC but I
> hope it uses a similar same technique as Orion.  I have
> NEVER heard any AGC pumping in Orion, even under
> severe situations like the CQ 160 CW Contest which
> I consider the ultimate test for any receiver.  I guess
> that's why it did not occur to me to mention it.  Maybe
> one of the Elecraft folk will tell us more abour the K3
> AGC.
>
>                         73,  Bill  W4ZV
>
>
>
> _______________________________________________
> 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

[romers romansky]

--- Don Wilhelm <[hidden email]> wrote:

> Bill,
>
> All of what you say is true *EXCEPT* for one item -
> and that is the AGC.
>
>
[...]

> Now, if the signal you are trying to copy is an S-1
> or S-2 level and an
> S-9 signal comes into the roofing filter passband
> (again it may be out
> of the DSP passband and will not be heard), the
> receiver gain will be
> reduced and you will no longer hear the S-1/S-2
> signal - just like QSB,
> but it is QSB induced in the receiver, not due to
> propagation effects.
>

Eeeeek! time to kill the agc and back down on the RF
gain and up the audio gain?

Best,
jerome - va7vv

[...]
> 73,
> Don W3FPR
>

_______________________________________________
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

[w2bvh]

Bill,

I've had my eye on the Orion since it came out. I almost got to the point of clearing getting one with my xyl, but about that time the QST review came out and it wasn't all that kind to the Orion. So I've held on to my K2. I've been happy with it, but it's human nature to always look for a bit more.

The reason I'm writing you is I'd like to know if you think the (2) QST reviews were unfair and what you think of the Orion... (Your reply, below, is quite complimentary; but are you coping with other deficiencies to get the raw performace the Orion is giving you?)

Tnx in advance & 73,
Lenny W2BVH
 -------------- Original message ----------------------
From: Bill Tippett <[hidden email]>

> At 07:34 PM 5/4/07, Don Wilhelm wrote:
>
> >All of what you say is true *EXCEPT* for one item - and that is the AGC.
>
>          Don you are absolutely correct.  The reason
> I never considered it is that I have never experienced it
> with my Orion.  I seldom operate with strong signals
> spaced much closer than 500 Hz.  The most severe
> case of this may be in the CQ 160 CW Contest where
> it's not uncommon for S9+20 to 30 signals to be spaced
> every 500 Hz.  With typical key click bandwidths, very
> few people will try to get closer than 500 Hz.  Given
> 500 Hz signal spacing and given a 500 Hz BW filter,
> the filter easily knocks them down to a reasonable
> level, since the filter BW is +/- 250 Hz and the signals
> are +/- 500 Hz.
>
>          Orion uses a two-stage AGC system, one is
> analog and ahead of the DSP.  It has has the main
> function of preventing over-driving the DSP stage.
>
> "ADC overload can never be allowed to occur because when that
> happens, signals are irrevocably corrupted. Signals that are larger
> than the full-scale range of the ADC must force reduction of gain in
> the analog section of the receiver. So both analog and digital AGCs
> are used in the Orion. Resort to analog AGC only need be made when
> signals inside the roofing bandwidth exceed about S-9 plus 30 dB. At
> that point, sensitivity is reduced but what we are discovering is
> that phase-noise performance-- as determined by reciprocal-mixing
> measurements-- already limits what you can hear. So performance is
> phase-noise limited and not DSP limited. Even so, the Orion gives you
> the option of kicking in a crystal filter, preventing movement of the
> analog AGC and the sensitivity reduction described above."
>
> http://www.doug-smith.net/orion.htm
>
>          As stated, this analog AGC does not activate
> until signals reach the S9+35 range.  The second AGC is
> digital and internal to the DSP (which works very well).
>
> "As the resolution and speed of ADC hardware improve, digital radio
> receivers become less dependent on analog AGC to meet dynamic-range
> requirements. State-of-the-art 24-bit IF-DSP converters, such as
> those used in the Ten-Tec Orion, produce about 100 dB of dynamic
> range. That means a receiver can handle signals from the noise floor
> to almost 40 dB over S9 without analog AGC. Above that level, analog
> AGC is still necessary to maintain the linearity of analog circuits
> and to prevent overload in the ADC hardware."
>
> http://www.doug-smith.net/dspdynamics.htm
>
>          I haven't seen much about the K3 AGC but I
> hope it uses a similar same technique as Orion.  I have
> NEVER heard any AGC pumping in Orion, even under
> severe situations like the CQ 160 CW Contest which
> I consider the ultimate test for any receiver.  I guess
> that's why it did not occur to me to mention it.  Maybe
> one of the Elecraft folk will tell us more abour the K3
> AGC.
>
>                          73,  Bill  W4ZV
>
>
>
> _______________________________________________
> 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

[Bill W4ZV]

Hi Don,

At 08:47 PM 5/4/07, Don Wilhelm wrote:

>I did ask Wayne about the AGC (with respect to the roofing filter
>selection) and he indicated that the AGC was developed in hardware
>before the A/D conversion and there is additional AGC action created
>in the DSP.  As I understand it, it is similar to that which you
>describe in the Orion.

         If it is like Orion's I'll be happy!

>Yes, from a receiver performance standpoint, only the A/D overload
>problem counts (and it is critical), but from an operating (AGC
>pumping) standpoint, there can be undesired performance in the
>presence of strong signals that pass through the roofing filter even
>though they are filtered out by the DSP because they will reduce the
>overall gain of the receiver.  Quite apart from the receiver specs,
>it does show up during operation and the AGC pumping can be a real
>problem for weak signal reception regardless of the total dynamic
>range of the receiver.

         I'm not sure I agree.  If analog AGC is
not activated, there is no analog gain change or
pumping.  According to the note I posted from
Doug Smith, the DSP can internally handle AGC
within the ballpark of 100 dB (noise floor to S9+40).
It first filters signals digitally and then applies AGC
only to signals appearing within the selected DSP
bandwidth, so there is no pumping by signals
outside the DSP bandwidth...unless I misunderstand
...which is completely possible of course!

         All I can say is I have never experienced
the problem in Orion.  I've got to get ready for a
symphony concert now so hopefully all will be
answered in the fullness of time!

                         73,  Bill


_______________________________________________
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

[Brett gazdzinski-2]

 
You seem to think the only time someone is going to
use wider bandwidths is on a packed band.

I personally only get on 80 or 40 on weekends, in the
morning, when the band is wide open.

You can say ssb is a waste, since its much wider than
CW.

Brett
N2DTS

>
> SSB - 2.7 kHz unless you want ESSB (not sure how high
> that goes these days but IMHO we should be trying to
> minimize communications bandwidths rather than playing
> broadcast disc jockey (my personal opinion!).  Those
> folks should go to 29 MHz FM if they want to do that.
>
> AM - 6 kHz
>
> FM - 15 kHz
>
>

_______________________________________________
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]

Keep up the good work Bill!!  May I second you request for comprehensive IMD
/ BDR  test results. Crystal filters, particularly ladders, do have a habit
of coming back to bite unless their linearity, or lack of, is taken into
account while setting Gain Distribution et al during the design activity.

I sometimes wonder whether the use of wide SSB filters e.g  2.7 kHz in our
ham community is due to poor narrower filter design,  and the reulting group
delay characteristic. This in turn can result in a SSB voice signal having a
"raspy" sound. In my opinion based on observation and use, 2.1 kHz  is
enough for very good soundimg audio IF things are set up properly (carrier
position, modulator AF drive, ALC, mic, etc, etc),  leaving more spectrum
for others to use.

73,
Geoff
GM4ESD


On Friday, May 04, 2007 at 7:59 PM, Bill Tippett wrote:
>
> SSB - 2.7 kHz unless you want ESSB (not sure how high
> that goes these days but IMHO we should be trying to
> minimize communications bandwidths rather than playing
> broadcast disc jockey (my personal opinion!).  Those
> folks should go to 29 MHz FM if they want to do that.
.
<snip>
>         A roofing filter's purpose is simply to minimize
> spurious artifacts from being created *inside* the RX
> by external signals.  It does NOT create the ultimate
> selectivity (which is determined by the DSP filter at
> the 2nd IF).  Please read the last sentence again!
> Here's a simple summary:

<snip>

> ...roofing filter prevents very strong signals from
> creating spurious (i.e. *NOT REAL*) signals which
> will then appear inside the DSP.

<snip>

>         The number of poles (i.e. shape factor of the
> filter) can affect IMD/BDR issues inside the RX.  For
> this reason hopefully Elecraft will provide actual
> IMD/BDR measurements with each option to help answer
> the following questions:
>
> 1.  Is the optional 8-pole 2.8 kHz better than the
> stock 5-pole 2.7 kHz (by "better" I mean resulting
> in better IMD/BDR performance which is the primary
> purpose of a roofing filter).

<snip>

>         The variable BW filters are interesting but
> I would not consider them until we have some actual
> results for IMD/BDR.  They are NOT providing ultimate
> selectivity as they do in the case of the K2, which
> seems to be confusing many folks.
>
>                                 73,  Bill  W4ZV


_______________________________________________
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

[Bill W4ZV]

>--- Don Wilhelm <[hidden email]> wrote:
>
> > Bill,
> >
> > All of what you say is true *EXCEPT* for one item -
> > and that is the AGC.
> >
> >
>[...]
>
> > Now, if the signal you are trying to copy is an S-1
> > or S-2 level and an
> > S-9 signal comes into the roofing filter passband
> > (again it may be out
> > of the DSP passband and will not be heard), the
> > receiver gain will be
> > reduced and you will no longer hear the S-1/S-2
> > signal - just like QSB,
> > but it is QSB induced in the receiver, not due to
> > propagation effects.

VA7W:
>Eeeeek! time to kill the agc and back down on the RF
>gain and up the audio gain?

         To some degree but you cannot actually kill AGC
in a rig like Orion (or perhaps K3 which apparently uses
similar analog plus digital AGC).  The reason is that the
analog AGC (actually more of a peak limiter) ahead of
the DSP must *always* be active to protect the DSP
from being over-driven.

         Your "Eeeeek!" sound is a good description
of the sound of a DSP that is over-driven.  In Orion
digital AGC in the DSP is also never fully turned off.
"Off" is simulated by setting AGC Decay to a high
rate (1000 dB/s) but it is never actually off even when
"Off" is selected on the front panel.  I've discovered I
can make it a little more "Off" by setting Decay to
2000 dB/s in the Programmable AGC mode, but that
is also not truly "Off" (which has an infinitely fast
decay rate).

         We can basically throw away some of our
ideas about AGC based on analog rigs like the
K2.  DSP rigs simply don't work the same way.
I'll repeat again...I've never heard classical AGC
pumping in Orion.  If you are using a 500 Hz filter
(+/- 250 Hz BW) and a S9+30 station is 500 Hz
away (then attenuated ~6 dB by the filter skirt),
you will hear keyclicks, phase noise, etc long
before you hear AGC problems.  Also "pumping"
is not a good description of a signal overdriving a
DSP.  To me It sounds more like a machine gun
suddenly going off next to your head.  It's more
of a digital (i.e. on/off) staccato effect...not the
classical analog gain pumping effect.

                         73,  Bill  W4ZV


_______________________________________________
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