Re: Grounded grid VHF front-end

On Sun, 10 Nov 2024 06:08:27 GMT, Jan Panteltje wrote:

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?
 

I'm sure Liz is aware there are far better modern alternatives out there,
Jan. However, this is (I believe) a purely fun project - and I've been
thinking for many years about doing a similar thing myself with tubes. In
fact I've retained a substantial collection of the damn things for
precisely this purpose. I always thought, 'one day I'll retire and I'll
have time to build something using these valves and it'll be a blast.'
Anyway, I retired 25 years ago and have even less time now for fun
projects than I had when I was working. Such is life...

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...

Dunno if you have any of the RSGB-published books by Pat Hawker (G3VA
IIRC) but he had several designs for very effective antennas at VHF and
UHF made from lengths of old coax. The emphasis was always on economical
designs with old Pat. He grew up in the shadow of WW2 where you had to
make do with what you found lying around in the rubble of bomb craters.