Elecraft

Elecraft Receiver

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Phil LaMarche

Elecraft Receiver

Even though I have a Collins R-388 that I use on AM, I would also purchase a
receiver immediately.

Phil K2 & KX-1

Philip LaMarche
LaMarche Enterprises, Inc.
www.instantgourmetspices.com
727-944-3226
(800) 395-7795 pin 02
Cell 727-510-5038
FAX- 727-937-8834
N.A.S.F.T # 30210
W9DVM

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N8LP

Re: Elecraft Receiver

I would love to see an actual K-RCV with low distortion synchronous AM
detector.

In the meantime, here's a concept I have been toying with building. The
R-388, like most Collins gear, uses front-end converters to shift a
whole band segment so that the rest of the receiver becomes a tuneable
IF. This brings back some of the problems associated with multiple
conversion receivers that the K2 beats the pants off of... but full K2
performance isn't as necessary in non-contest general coverage conditions.

I'm thinking of a strong passive mixer preceded by selectable filters,
and followed by a 500 kHz wide bandpass filter. Collins used 200 kHz
segments on the S-Line, but for simplicity I think 500 kHz would have to
suffice. The LO would be adjustable in 500 kHz steps, with a LED display
to show the 3 most significant digits of received freq, ie.13.0, 13.5,
etc. LO output could be 7.5-37 MHz to cover .5 - 30 MHz, making the
converter output 7.000 mHz. You would have to ignore the first couple
digits on the rig's readout. You could feed the converter output to the
2nd antenna input on the K2. The preamp in the K2 would need to be used
to overcome losses in the front end.

Not the best solution, but a workable one for those who do occasional
listening outside the ham bands.

Larry N8LP

Phil LaMarche wrote:

>Even though I have a Collins R-388 that I use on AM, I would also purchase a
>receiver immediately.
>
>Phil K2 & KX-1
>
>Philip LaMarche
>LaMarche Enterprises, Inc.
>www.instantgourmetspices.com
>727-944-3226
>(800) 395-7795 pin 02
>Cell 727-510-5038
>FAX- 727-937-8834
>N.A.S.F.T # 30210
>W9DVM
>
>
>
>
>
>
>

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N8LP

Re: Elecraft Receiver

In reply to this post by Phil LaMarche

It was correctly pointed out to me off-list that my example of a 7 MHz
"IF" would tax the input filters in order to get the best image
rejection. I used that example since it was the first band that starts
at "000".

The filtering requirement could be relaxed considerably by using a 28
MHz "IF". The PLL synth chip I am looking at is good to 185 MHz...
moving the LO to 28.5 - 56 MHz would cover .5 - 28 MHz... the converter
wouldn't have to cover 28-30 MHz since the K2 does that. It would also
keep the sidebands consistent for all frequencies.

I was thinking of using a PIC to control the counter in the PLL, UP/DN
buttons to change bands... and a 3 1/2 digit LED display to show the
first three digits of the receive frequency.

Larry N8LP

Phil LaMarche wrote:

Geoffrey Mackenzie-Kennedy-2

Re: Elecraft Receiver

In reply to this post by N8LP

Hi Larry,

Defender of the Multiple Conversion Faith charging in !

> In the meantime, here's a concept I have been toying with building. The
> R-388, like most Collins gear, uses front-end converters to shift a
> whole band segment so that the rest of the receiver becomes a tuneable
> IF. This brings back some of the problems associated with multiple
> conversion receivers that the K2 beats the pants off of...

Glad that you said "associated" and not "occur"! The high IF receiver runs
circles around the low IF receiver in spurious response / internal birdie
performance IF the IFs are chosen properly and IF High Side mixing is used,
all assuming that the right devices / circuits are used. The choice of IF
and High Side mixing and devices /circuits applies to low IF receivers, but
in their case there is a much smaller choice of IFs, even just for HF ham
band coverage,and they must have good front end filters and internal
shielding if one wants a "clean" receiver. I would suggest that the problem
with "commerecial" High IF double conversion receivers for Amateur use,
which has created the myth, has three parts 1) The technology used is not up
to date in this fast moving field - it cannot be. 2) The production roofing
filters are wide as barn doors, and the "retrofits" are not much better if
you look down their skirts and their distortion contribution, who knows 3)
Usually the choice of IFs appears to be driven rather than chosen.

The main ham band only receiver here, homegrown, is double conversion first
to low VHF where the roofing filter bandwidth can be selected - 1.5 kHz
narrow.It is a "strong" receiver without any internal spurii above noise
floor. Took much number crunching, but that occupied waiting time at
airports.

I think that tuneable IFs are attractive for general purpose use if really
good intermod performance is not sought , although it can be if one stays
away from diode ring mixers and uses modernish "strong" mixers and
amplifiers. Also opens the option for low noise crystal oscillators for the
first LO in those bands where one needs low phase noise from the LO. Collins
also had an an eye on frequency readout, and further opted for the low
values of IF / Signal Freq ratios, perhaps for VFO stability reasons, but
because of the strong spurious responses on the high side, 2Fo - 2Fa = IF
etc (where LO was high side), they needed good front end filters. So it
might be worthwhile looking at say 24 or 28MHz as an IF. But beware of the N
times signal frequency = IF monkeys, and friends.

Good luck with whatever you do.

73,

Geoff
GM4ESD

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N8LP

Re: Elecraft Receiver

Thanks for the comments Geoff. As I think it through more, I will have
to weigh the compromises, but I think a workable design can be done. I
will work up a test board using my HP sig gen for injection, a
Mini-Circuits DBM and some Coilcraft 7-pole filters I have on hand for
the mixer and preselectors... and make some measurements. I'll order
some of the PLL chips as well. I think it will be a fun project. I also
always wanted to play with variable preselectors... there was a good
article in QEX about 5 years ago that might be a good jumping off point.
I can use a PIC to control it all... I'm always on the lookout for a
good PIC project ;-)

Larry N8LP

Geoffrey Mackenzie-Kennedy wrote:

>Hi Larry,
>
>Defender of the Multiple Conversion Faith charging in !
>
>
>
>>In the meantime, here's a concept I have been toying with building. The
>>R-388, like most Collins gear, uses front-end converters to shift a
>>whole band segment so that the rest of the receiver becomes a tuneable
>>IF. This brings back some of the problems associated with multiple
>>conversion receivers that the K2 beats the pants off of...
>>
>>
>
>Glad that you said "associated" and not "occur"! The high IF receiver runs
>circles around the low IF receiver in spurious response / internal birdie
>performance IF the IFs are chosen properly and IF High Side mixing is used,
>all assuming that the right devices / circuits are used. The choice of IF
>and High Side mixing and devices /circuits applies to low IF receivers, but
>in their case there is a much smaller choice of IFs, even just for HF ham
>band coverage,and they must have good front end filters and internal
>shielding if one wants a "clean" receiver. I would suggest that the problem
>with "commerecial" High IF double conversion receivers for Amateur use,
>which has created the myth, has three parts 1) The technology used is not up
>to date in this fast moving field - it cannot be. 2) The production roofing
>filters are wide as barn doors, and the "retrofits" are not much better if
>you look down their skirts and their distortion contribution, who knows 3)
>Usually the choice of IFs appears to be driven rather than chosen.
>
>The main ham band only receiver here, homegrown, is double conversion first
>to low VHF where the roofing filter bandwidth can be selected - 1.5 kHz
>narrow.It is a "strong" receiver without any internal spurii above noise
>floor. Took much number crunching, but that occupied waiting time at
>airports.
>
>I think that tuneable IFs are attractive for general purpose use if really
>good intermod performance is not sought , although it can be if one stays
>away from diode ring mixers and uses modernish "strong" mixers and
>amplifiers. Also opens the option for low noise crystal oscillators for the
>first LO in those bands where one needs low phase noise from the LO. Collins
>also had an an eye on frequency readout, and further opted for the low
>values of IF / Signal Freq ratios, perhaps for VFO stability reasons, but
>because of the strong spurious responses on the high side, 2Fo - 2Fa = IF
>etc (where LO was high side), they needed good front end filters. So it
>might be worthwhile looking at say 24 or 28MHz as an IF. But beware of the N
>times signal frequency = IF monkeys, and friends.
>
>Good luck with whatever you do.
>
>73,
>
>Geoff
>GM4ESD
>
>
>
>
>
>
>
>
>
>

N8LP

Re: Elecraft Receiver

In reply to this post by Geoffrey Mackenzie-Kennedy-2

As I think more about it Geoff, I would need a pair of mixers in order
to get the tuning right-side up again. A first conversion to, say 45
MHz... and a second back to 28 MHz. Injection would be from a xtal osc
for the first conversion and a VCO running in the 46-73 MHz range. High
side injection on both would get the tuning back to right-side up. With
two mixers, a strong mixer amp would be required between stages. I have
a couple designs I have used with good success that are easy to
implement there.

I can see this will take some thought to get the right set of compromises.

Larry N8LP

Geoffrey Mackenzie-Kennedy wrote: