K2 and FM

[seumasd]

Hi

Any possibility of FM facility for the K2?    Preferably on both RX and TX, but on RX only would be handy especially when using transverters on VHF.

73                JimD, GM3UAG
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[Don Wilhelm-3]

The fine folks at Elecraft may prove me wrong, but ---
I doubt an FM addition to the K2 would be practical.  It may require a wider
bandwidth filter for the IF, likely the addition of a limiter and an FM
detector for the receiver, which likely would be easiest implemented as a
separate IF strip.  A transmit solution may be more practical because that
would just require an addition to the PLL/VCO circuits.

There is a chance that such a conversion would fit into the basic K2
enclosure, but it certainly would not fit in the K2/100.

73,
Don W3FPR

----- Original Message -----
Any possibility of FM facility for the K2?    Preferably on both RX and TX,
but on RX only would be handy especially when using transverters on VHF.



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[John Payne-5]

I have not tried it, and it may not work well on an SSB rig due to the
BFO.  When I was just a young squirt, we used to slope-detect FM on our
good old Heathkit Benton Harbor Lunchboxes which were broad as a hanger
door, and other AM rceivers(Gooney Boxes, etc.).  Worked pretty well,
but there was no BFO to contend with.  The BFO will no doubt cause a
beat-note which could be quite annoying while trying to slope-detect FM.
  Perhaps a way to defeat or turn off the BFO?  May not be practical on
the K2, just a thought.  BTW, as I understand it, slope-detection means
that one tunes the FM signal such that the signal is down on the "slope"
of the IF response curve, which causes the detector to act as an FM
detector to an extent, recovering audio from an FM signal.  If any of
the above is wrong, I am most willing to be corrected!

73 de John N4FLJ

seumasd wrote:

> Hi
>
> Any possibility of FM facility for the K2?    Preferably on both RX and TX, but on RX only would be handy especially when using transverters on VHF.
>
> 73                JimD, GM3UAG
> _______________________________________________
> Elecraft mailing list
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>

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[Geoffrey Mackenzie-Kennedy-2]

Not impossible Jim for Rx - a good selection of adequate "FM Receiver" ICs
around.  Tx more difficult as you don't want to increase the LO's phase
noise.for CW/SSB - but could be done without touching the VFO. But where do
you put it all without introducing problems?

73        Geoff    GM4ESD


----- Original Message -----
From: "seumasd" <[hidden email]>
To: "Elecraft Digest" <[hidden email]>
Sent: Thursday, November 18, 2004 10:05 PM
Subject: [Elecraft] K2 and FM


Hi

Any possibility of FM facility for the K2?    Preferably on both RX and TX,
but on RX only would be handy especially when using transverters on VHF.

73                JimD, GM3UAG

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[G3VVT]

Why on earth would you want to possibly compromise the excellent  performance
of the K2 when there are cheap purpose built FM transceivers in  abundance on
the market and second hand they can be picked up for  peanuts?
 
Even without this in mind the immediate problems are:
 
Receiver.
 
Even with using the narrow band FM we have been bullied into adopting in  the
UK for repeaters, the +/- 2.5kHz deviation will not pass through the 2.0 to  
2.5kHz filters found in the K2. The effect is to cut the carrier off on  
deviation peaks producing what has been nicknamed here the "Norman Collier  effect"
by causing the squelch to close at this instant and chopping up the  received
audio to make it unintelligible. As a repeater license keeper and  builder am
acutely aware of this effect by mobiles trying to force a +/- 5kHz  signal
though our now mandatory 7.5kHz (+/-3.75kHz) bandwidth  filters.
 
I just does not work!
 
For +/-5kHz deviation an IF filter of 15kHz (+/- 7.5kHz) is the norm. To  
incorporate this in the K2 would mean extracting the IF signal soon after  the
1st mixer Z6 and before the K2 1st IF filters. A totally separate IF,  squelch
and FM detector strip would be needed with most probably 15kHz  filters to cope
with older transmitters. Additionally this would really  need to be an
outboard unit with its own audio amp and speaker. IC's such as the  now obsolete?
MC3357 would take care of all the IF, squelch and detector  functions.
 
Transmitter.
 
FM on transmit could be produced by feeding audio via a suitable coupling  
capacitor into the K2 VCO control line, though the deviation would probably not  
be constant on all bands. There is a problem with the TX audio as the peak  
deviation has to be strictly limited in its amount. Even the use of a
compressor  just does not give the degree of control needed, so an audio peak limiter  
stage and subsequent following low pass filter has to be inserted.
 
All in all do you really want to do this when again it could compromise the  
excellent performance of the K2?
 
Bob, G3VVT
Keeper (license holder) GB3LD/GB3LF
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