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From: Jan Panteltje <alien@comet.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Grounded grid VHF front-end
Date: Sun, 10 Nov 2024 06:08:27 GMT
Message-ID: <vgpiks$e1ei$1@solani.org>
References: <1r2rj8l.msi28f14weovyN%liz@poppyrecords.invalid.invalid>
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On a sunny day (Sat, 9 Nov 2024 16:35:45 +0000) it happened
liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in
<1r2rj8l.msi28f14weovyN%liz@poppyrecords.invalid.invalid>:

>My current receiving aerial system is very inefficient at 2 metres (144
>Mc/s) and I have thought about making a sleeve dipole for that band.  My
>VHF receiver is an Eddystone 770R, which covers the band but only in a
>small portion of the whole scale.  While I am improvomg the aerial
>system, I could also make a crystal-controlled down-converter, that
>would allow me to use an HF communications receiver or the lower ranges
>of the 770R, so that the  band 2 Mc/s wide would cover a much greater
>scale length.

Have you ever considered using a RTL_SDR stick and a PC or Raspberry program for reception?
Something I wrote for it:
 https://panteltje.nl/pub/xpsa-0.7.gif
  those sticks cover from about 20 MHz to 1.6 GHz
More abou those here:
 https://www.rtl-sdr.com/about-rtl-sdr/
even used one to receive GPS signals
Those sticks are about 40? dollars on ebay, accuracy 1 ppm.
 https://www.ebay.com/itm/276000566513?



>It's been a few years since I designed anything with valves, so I
>thought I might have a go at making a down-converter using valves - but
>not necessarily the expensive 'cult' ones which everyone seems to regard
>as having magical powers.  The EF91 is plentiful and cheap as New Old
>Stock, so that seems like a good valve to start playing about with.

I remember ECC85 in FM tuners, should be fine at 144 MHz:
 https://www.radiomuseum.org/tubes/tube_ecc85.html

That circuit diagram shows an about 100 MHz to 10.7 MHz FM radio input stage + mixer.
I have used that tube a few times.

But transistors took over, and now chips like in that RTL_SDR stick, are hard to beat.

Sometimes I just strip some coax at the right length for antenna:
 https://www.panteltje.nl/pub/DVB-T2_antenna_IXIMG_0757.JPG
Have some yagi antennas too, and even an old TV rack..
And a big 27 MHz GPA antenna somewhere...