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Sunday, December 27, 2015

"Receiver Here is My SWR meter OM..."

Santa managed to include in his delivery some of the materials that I needed to build my 160 meter inverted L antenna.   You see, Steve Silverman, Pete Juliano and I have collectively more than 150 years in ham radio, but none of us have ever operated on Top Band.  The three of us have taken A SOLEMN OATH to correct this horrendous deficiency.   I am in the vanguard, partly due to a weather pattern that is perfect for antenna building. 

Armed with a new elastic band for my Wrist-Rocket sling shot and some perfectly shaped lead sinkers,  yesterday -- with the obvious cooperation of The Radio Gods -- I managed to get two ropes over some 70 foot trees.  Soon -- with minimal gnashing of teeth -- I had 185 feet of wire in the air. 

This morning I was messing around with L networks at the base of the antenna.  I took a coffee break, leaving the 185 foot wire and the ground system connected to the coax.   I had the transmitter off, so I was surprised to see the SWR meter jumping around a bit, up significantly from zero.   What could that be?  It wasn't coming from my station, so it had to be coming from some other transmitter. And the slight bit of jumping that I saw on the SWR meter had the familiar pattern of the human voice.  Some radio sleuthing ensued.

I flipped the station antenna switch to the  "bench" position, and connected my scope to the coax.  Wow!  I immediately saw a big strong AM signal with modulation, at about  5 or 6 volts peak to peak.  The Rigol 'scope gave the frequency:  1220 kHz.  

I tuned the HQ-100 to that frequency.  As I listened to Gospel broadcast, I could follow the voice peaks on the 'scope. 

Some Googling ID's the station:  WFAX 1220 AM.   5 kilowatts in the daytime.  1.5 miles from my house.  The vertical portion of the inverted L is obviously picking up a LOT of energy from the WFAX tower.  And the horizontal portion of my antenna is broadside to the WFAX tower.

Of course this all made me think about throwing together a crystal radio, but then I realized I'd already listened to WFAX with simple diode -- the one in my SWR meter.  That little SWR meter was acting like a crystal radio with a visual output!     

5 comments:

  1. With this much RF available out of thin air, throw an electrolytic cap across the diode output and you have the makings of a "free power" source that can power a couple of transistors for an audio amplifier. You will have a "free power" radio receiver that can run a small speaker. Fun!

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  2. There is a great article in January, 2016 QST on how to roll your own BCB reject filter. Pg. 69

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  3. Bill,
    Strong local signals like this can challenge many receivers as the frequency and TX is so close and your wire long. I run my inverted L as a folded monopole as written up in the past by Bill Orr. Not only does this provide an impedance transformation to something close to 50ohms it seems to attenuate off frequency signals.
    http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/hr/1990/03/page49/
    I use zip cord speaker wire. It is bit shorter than 40m because of the velocity factor of the wire in transmission line mode.
    Andrew de vk5cv / vk5zuc@hotmail.com

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  4. I remember a schematic - I could probably replicate it - for a crystal AM receiver, that used a second tuned stage (but fixed, to the strongest station in your area) to power a transistor amplifier for (modern, not crystal) headphones.

    Mike Yancey, KM5Z
    Dallas, Texas

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  5. Bill,
    You are missing an opportunity to have "free" electricity. When not operating on 160M you need to gin up a voltage doubler circuit and with that you can charge batteries or run your Frankenstein Radio off of that power source. I think this idea originally appeared in a "transistor radio circuits book" from Tom Kneitel

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