[Lowfer] down and out low down

[Bill Ashlock]

Eric,

Relative to building Lowfer transmitters, the Lowfer receiver is 100 times 
more critical. Some of the important characteristics are:

1) Very narrow selectivity, but at the same time, very good impulse 
response, IE: very low ringing in response to noise.
2) Good frequency stability. And if used for QRSS - Very, very good 
frequency stability.
3) High gain.
4) Good rejection and low IM in response to strong out-of-band signals.

These tight requirements are the reasons why no LF receiver kit is available 
at the present time - with the possible exception of a direct conversion 
receiver (which only partially meets the above criteria).

I've mentioned from time to time about measurements with my portable SVM. I 
spent almost a solid year of spare time designing this receiver  with the 
aim of making it solid, RF-wise, so that it can be built and tuned up in kit 
form, without the normal oscillations from misplaced wires, and slightly 
mismatched components. This receiver comes close to beating my R75 on low 
level signal grabbing but has totally inadequate frequency stability for 
QRSS use. I had a PCB layout about 99% complete a year ago and lost the 
inspiration when all the TX loop activity began. By coincidence, last night 
I located a source for a LO xtal that would allow QRSS reception of the 
185.3 group plus a little extra ground and am anxious to purchase a sample. 
There have been a number of other guys interested in a PCB blank so I'll try 
to get this project re-started as soon as I pass the code exam.

Bill

>From: Eric Smith <eric@willow.nutstreet.net>
>Reply-To: lowfer@mailman.qth.net
>To: lowfer@mailman.qth.net
>Subject: [Lowfer] down and out low down
>Date: Wed, 23 Apr 2003 20:08:37 -0500 (CDT)
>
>While the audio final has been out in my GT-550, I've been able to use a
>crystal earphone :)
>
>Now, RF is out.  I don't know if it is the front-end or the finals, but
>the S-meter doesn't even move when I tune around.  Dead as a doornail.
>
>There are about two $500 expenditures I need to make before I'd feel very
>good about spending $500 on a radio.
>
>In about 15 minutes I can build a radio that will pick up the AM broadcast
>band with an oatbox, a length of wire, a resistor, a 1N34, and my trusty
>crystal earphone.  Of course, those stations are 50,000 watts :)
>
>But it looks like I could build a more complex circuit (with some RF
>amplification and better selectivity) that would work BELOW 500 kc,
>without going to the complexity of a synthesized tuner.
>
>I have plenty of 365pf air variables :) and thousands of feet of telephone
>wire.
>
>Do any of you know where I might find such a circuit?  Point me to a
>schematic, and I'll build it!
>
>Thank you,
>Eric, KD5UWL, hurting BAD in EM25


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