Re: Valve frequency multipliers

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

On 2.2.2025 23.10, Liz Tuddenham wrote:

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.
 
 

 
You're starting with a too low IF. The standard method for 2 meter
transverters is to start with a 28 MHz band signal, to get the images
far enough to use less complicated filters after mixing. You have to
be careful about oscillator signal leaking through the mixing process
anyway.

My first 2 metre receiving setup had a crystal-controlled down-converter
and a CR100 communications receiver running at 28 Mc/s.  The CR100 was
so unstable that it would shift several Kc/s if a gnat landed on the
front panel.  I improved the mechanical design, which was very poor, and
made it useable but it was never particularly stable.

Using a VFO on the transmit side requires an even better degree of
stability, which is why I chose to keep the crystal-controlled frequency
high and use a more stable lower frequency VFO to generate the
transmitting frequency.  The VFO coil is wound on a ceramic former and
bonded with epoxy resin to reduce expansion of the copper wire.  I have
made provision for temperature compensation and checked that the
frequency drift with changes in the H.T. voltage are negligible.

On the receive side, the first down-conversion ratio is 145 to 5 Mc/s
i.e. 29:1, the second ratio is 5 Mc/s to 100 Kc/s i.e.50:1.  If these
were stupidly different I would be very worried, but they aren't too far
off the ideal of both being 38:1 and the greater ratio is at the lower
frequency, where filtering is easier.

 
The 160 MHz bands are for maritime mobile services.

Luckily I live far enough from the sea that my transmissions will never
get to the coast.  If I go portable, the highest land is still some way
inland and my maximum output is less than 10 Watts, so I don't think
there is likely to be much of a problem.

<nag>
Megacycles / second have been buried even in the US for over half a
century. The current radios use MHz or GHz.
</nag>

Yes, I know  ...but I am well over half a century old and I prefer Mc/s.


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