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Re: LF: 136kHz receivers

To: [email protected]
Subject: Re: LF: 136kHz receivers
From: Väinö Lehtoranta <[email protected]>
Date: Thu, 30 Sep 1999 15:24:41 +0300
In-reply-to: <[email protected]>
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
The art of listening (band monitoring),

Earlier this week I was almost sorry that I once again
triggered the discussion about receivers and listening
strategies. I did so because AR-7030 Plus - sort of
unexpectedly - appeared to offer endless possibilities
to improve listening at this lousy qth -- why not move
somewhere else then, you don't wish to ask my lady..?
By the way, at my last job Racal 1792 was the main tool
used for monitoring, band scanning, with Racal DF etc.
Some OH friends still have good use for Racal 117 etc.

Still, no idea how much AR-7030 and AR-7030+ differ?
For mobile type individuals AR sure is easier to carry.

After reading all those nice comments there was after
all no reason to be sorry. Perhaps some people have
gathered some new ideas. Just a few more comments.

For our purposes there was seldom any need to make
conventional Rx S/N measurements but just a test for
minimum indicated (by ear?) rx input level test.
Perhaps time has come that only amateurs can any more
enjoy copying (by ear?) cw type signals weaker than
anyone can expect to be copyable? Not all can enjoy
conventional cw which for our generation was obligatory.

I sort of remember that Collins type mechanical filter
was first introduced in connection with 51J-1 around
1951 (?) We used to have whole string of them, the last
one, 51J-4 is still available here but with stuck gears.

The cw filter bandwidth has been discussed ever since.
Some people like narrow but world famous(?) OH contesters
seldom seem to prefer as narrow as 100 Hz. I remember
that my late good friend Helge, OH2ZE, then at Motorola
built a very narrow filter (1-2 Hz) already in the 70's.

Have been following EME & Weak Signal Pages for some
time. They talk about receive tests at -171 dBm and
even -179 dBm levels; I have a couple of versions of
FFTDSP (by AF9Y), also SbFFT v 1.2 (by KW5Q) but for
some reason my favorite is Specgram (by PhilvanBaren).
I have had more than 10 versions of Gram (by RSHorne).
Just like different receivers these programs all have
desirable properties suitable for some specific mission.
It is amazing how useful these 'SB scanners can be!

73 de Vaino, OH2LX







At 22:01 29.9.1999 +0100, you wrote:
Hi all,

I agree with Toni observing that a 500 Hz filter is too wide
for serious weak signal work.

I use a Racal 1792, modified with 300 Hz and 100 Hz filters,
followed by an audio (analogic) filter. The 100 Hz one, if
well designed (no appreciable ringing) helps a lot.

I also tried an attenuator in front of the RA1792. In my
location I have no need for it; I prefer to reduce the IF gain.
The first mixer seems tough enough (103 dB 3' order IMD measured).

Vaino, are you sure those RX are not designed for weak signal
work? In my opinion it is VERY good. I also tried many others,
and I keep the RA1792 as my main RX.

73 - Marco IK1ODO
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V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
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