Re: Valve frequency multipliers

Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:

On 1.2.2025 17.30, Liz Tuddenham wrote:

legg <legg@nospam.magma.ca> wrote:
 
[...]

>
I'd be more selective of the crystal frequency. Two triplers might get
you there with a lot less grief.

 
I regret to say I think you are right   :-(
 
Quintuplers just don't seem to work in those circuits so I have placed
an order for a 16.656 Mc/s crystal, which will triple-triple to 149.904
Mc/s.  That will mean bringing the VFO down to a range of 3.904 to 5.904
Mc/s, which should be relatively easy.
 
Revised block diagram at:
http://www.poppyrecords.co.uk/other/Transceiver/BlockDiag6a.gif
 
It will make image rejection in the second receiving mixer a little more
difficult  The transmitting mixer is intended to be balanced, so
rejecting 149.904 Mc/s instead of 150.000 Mc/s from the output will not
be any more difficult but I may require an extra tuned circuit in the
later part of the transmitting chain to reduce the level of image
frequency.
 
I just hope the new crystal will work in the same circuit as the old one
and I won't have all the hassle of redesigning it.
 
 

 
Liz: You should not attempt to transmit anything around 150 MHz. It is
on a frequency band reserved for satellite communication, and any
unlicensed transmission is strongly frowned at.

I am being very careful to avoid transmitting any spurious signals at
150 Mc/s; the U.K. Amateur Radio band is 144 - 146 Mc/s and I  am only
allowed to transmit within that band. 

The block diagram (referred to above) shows that the 150 Mc/s output of
the multiplier chain is mixed with the output of a variable frequency
oscillator to give a signal in the 144 - 146 Mc/s band.  A balanced
mixer should attenuate the 150 Mc/s signal and further filtering removes
any remaining residual 150 Mc/s and the image freqency (164 - 166 Mc/s).

In an earlier design I proposed a low-side input to the mixer at 135
Mc/s but abandoned this when I realise that the image would be 124 - 126
Mc/s:.  This is in the band allocated to aircraft and I live undeneath
the flight path to Bristol Airport.


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk