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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Re: Valve frequency multipliers
Date: Mon, 3 Feb 2025 15:03:36 +0000
Organization: Poppy Records
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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 ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk