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From: Tauno Voipio <tauno.voipio@notused.fi.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Valve frequency multipliers
Date: Mon, 3 Feb 2025 21:20:31 +0200
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On 3.2.2025 17.03, Liz Tuddenham wrote:
> 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.
> 
> 

So am I, and I succeeded to abandon megacycles in favour of SI units
60 years ago.

-- 

-TV