[AK-VHF] external LO for XVTRs

[Edward R Cole]

Ron,

That is a very unconventional approach.  Typically transceivers 
merely mix fixed LO frequency with the tunable frequency of the IF 
radio.  Of course these days synthesized LO's are being used more 
often (I use them at 432 and above).  They typically are utilizing a 
phase-locked VCO which referenced to a frequency standard such as 
10-MHz.  This accomplished by digital division of the operating 
frequency down to match the reference frequency and phase shift 
measured as output of the PLL mixer.  Most have very narrow bandwidth 
to keep the phase shift tight and that typically results in a long 
lock-up time which would preclude real-time AFC.

But I have to ask why you feel that you need real-time AFC during 
transmit?  About the only ham radio application where rapid rates of 
frequency change occurs due to Doppler is near-earth satellite 
operation.  I have not operated on satellite for over ten years but I 
recall that Doppler correction is normally done by Rx tuning.  There 
is a satellite mode which tunes both Rx and Tx but I think its 
sufficient to do that over a few minutes duration which would allow 
Tx tuning during the receive period.

Eme does not suffer such high rates of Doppler change and its 
sufficient to set Doppler offset less often (usually manually).  I 
operate 23cm eme and can tell you that Doppler offsets do not need 
change that often.

Your approach of tuning the transverter LO is one that you would be 
on your own in designing.  But is it really needed?

73, Ed - KL7UW

At 05:39 PM 4/5/2017, Ron VE8RT wrote:
>    I was looking into using my Elecraft K2 with transverters to get onto
>VHF and above.  But I found online postings that HF transceivers may
>not be able to do Doppler correction while transmitting, that is the
>CAT input for frequency change is not decoded during transmit.  So I
>thought that there may be a way around that by having the radio control
>data go to the transverter instead.  For example say I wanted to have
>Doppler correction on a 23cm transmitter, I would like to preset the K2
>to a particular frequency and leave it there for the duration of the
>operation as a fixed IF while making any needed frequency changes
>through the CAT cable to the transmitter / receiver to the local
>oscillator in the transverter.  If this is a practical solution, has
>anyone offered CAT interfaceable oscillators for transverters?
>
>    Is the idea practical?
>
>    Ron VE8RT, Yellowknife, NT, Canada
>
>--
>Ron VE8RT <ve8rt at yknwt.ca>
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73, Ed - KL7UW
   http://www.kl7uw.com
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