Re: [IRCA] How to ID an unmodulated LW carrier?

[Tim Hills <thills@xxxxxxxxxxxxx>]

For your loop frame the gray PVC electrical conduit is UV resistant but 
not as rigid as Sced. 40 but I had an active SW antenna housed in Sced. 
40 that was exposed to -35F to over 100F in direct sunlight for 6 or 7 
years with no noticeable deterioration.

I use back to back varactors for tuning my loops. The MVAM109 and MV209 
varactors can be found on Ebay fairly cheap. using 20 of the MVAM109s 
gives a capacitance range from 200 to over 4000pF. Some of the surplus 
varactors are noisy so a bit of testing is required, about 1 in 20 or so 
fail but make good broadband noise generators so not all is lost.

Some people don't like the varactors  but my 30" MW loop has a very 
sharp null and high enough Q that even with a 10 turn pot tuning can be 
bit touchy. Driving more than about 10 of them requires an op-amp to 
correct for increased current. I use a dual bifet op-amp for tuning and 
gain buffers.

One of these days I'll have to post some schematics. Have to find a 
proggie to do it with first since my hand drawn stuff may as well be in 
hieroglyphics to anyone else. Anyone got any suggestions?

Tim Hills
Sioux Falls, SD

On 8/20/2011 20:10, Stephen Airy wrote:
> Oh ok, that sounds quite likely.  I plugged their coordinates into the FCC's distance finder and I'm about 18.5 miles away at a heading of 69°, which seems to match the direction I was aiming for the strongest signal.  It wasn't demodulating at all on my AM PL-606 - it sounded just like a broadcast signal does when it has just an unmodulated carrier with no program content, just a lot narrower when I tuned off frequency (if it makes any difference with non-modulation).  Anyway I looked up the coordinates on Google Maps, and it appears to be in the area where the Point Loma lighthouse is.
> And yes, I'm wanting to build a loop (or a few) sometime.  I'm just not sure what type of frame I want to use, yet.  I know a crate loop is out of the question due to needing to keep it a reasonable size and make it collapsible.  I've been considering a PVC frame loop like in Gary DeBock's articles, but when I was mentioning the idea to my dad, he thought the PVC wouldn't hold up as well in our weather here, where it can exceed 100°F with low humidity in summer. 
>   
> Also I'd need to figure out what type of capacitor to use.  (It would definitely be one of the larger types like what Gary uses in his projects, not the little cheapies that come with analog-tuned AM and FM radios.)  I'm just wondering if there's a way to get a better shape factor (flatter top, steeper sides, greater total off-frequency attenuation) by using a double or triple-gang capacitor in the design and 2 or 3 coils accordingly?

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