[ARC5] Crystal Question

[J. Forster]

A bit more.

Joints is any kind of conductors can be non-ohmic, including pipes,
electrical conduits, and even ground connections on Romex or BX runs.

A sniffer loop that works well can be easily made like this:


================= ================
================= ================  Pipe

          |----------------|
          |----------------o---------------> to Rx tuned to IM product

The loop is actually something like RG-58 or RG-174. The joint is as follows:

                            |||
                            |||
                            |||
                             |
            -----------------o--------------------
            -------------------------------------->  To Rx
            --------------------------------------

In words, the shield at the end is trimmed back and the center conductor
soldered is soldered to the braid.

Best,

-John

====================






> Dennis/John:
> Good example, good response.  Most informative.  Thanks vy much.
>
> Les
>
>
>> ----- Original Message -----
>> From: "J. Forster" <jfor at quik.com>
>> To: "Dennis Monticelli" <dennis.monticelli at gmail.com>
>> Cc: "Discussion of AN/ARC-5 military radio equipment."
>> <arc5 at mailman.qth.net>
>> Subject: Re: [ARC5] Crystal Question
>> Date: Fri, 12 Nov 2010 09:18:12 -0800 (PST)
>>
>>
>> A shielded current loop and portable SW receiver ids the easiest way to
>> track them down.
>>
>> -John
>>
>> =============
>>
>> > Not only rain gutters but wire fencing or decrepid old TV antennas or
>> any
>> > long metal run that has metal-to-metal mechanical contacts along the
>> way
>> > that corrode upon exposure to reactive elements in the atmosphere.
>> Nearby
>> > AM BCB antennas are the usual source of the fundamental energy.  I
>> > recently
>> > experienced terrible mixing products in my HF receivers that took
>> weeks to
>> > track down.  It turned out to be a hairline broken connection at the
>> > feedpoint of one of my wire antennas. The wire was copperweld and the
>> > connection was covered with RTV.  All looked well from the outside and
>> in
>> > trasmit the SWR was just fine as the large signal crashed right across
>> the
>> > gap.  But inside was a barely touching joint that had failed due to
>> > fatigue
>> > and in receive it made a great Schottky detector.
>> >
>> > I think the liquid electrolyte rectifiers of old were used in the
>> early
>> > power supplies.  The speed of ion transport in solution was probably
>> too
>> > slow to be useful as an RF detector.
>> >
>> > Dennis AE6C
>> >
>> > On Fri, Nov 12, 2010 at 8:01 AM, J. Forster <jfor at quik.com> wrote:
>> >
>> >> > Good Morning (UTC +1 time),
>> >> >
>> >> > Re my comment yestereday about metal-on metal
>> >> > rectifying RF:
>> >> > One of my experiments was using the contacts
>> >> > on my J-38 and home brew keys as detector
>> >> > by adjusting the spacing so that the
>> >> > oxidized contact surfaces barely made contact.
>> >> >
>> >> > On the more curious side, some have experienced
>> >> > having there tooth fillings function as detectors of broadcast
>> >> > signals.
>> >> >
>> >> > One of the causes of TVI often seen in densely populated areas
>> >> > is the fact that overlapping metal objects (e.g. rain gutters) not
>> >> > having good galvanic connection will rectify RF transmissions
>> >> > and create harmonics.
>> >>
>> >>
>> >> This is certainly true. A friend lives near a few powerful AM
>> stations
>> >> and
>> >> gets third order mixing products all the time. He has spent weeks
>> >> chasing
>> >> then down.
>> >>
>> >> Best,
>> >>
>> >> -John
>> >>
>> >> ==============
>> >>
>> >>
>> >> > BTW didn't early radio detectors also include liquid electrolytic
>> >> > solutions?
>> >> >
>> >> > Henry, Cph.
>> >>
>> >>
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