AM Radio (antennas)

Posted by: Russ

AM Radio (antennas) - 10/16/19 04:36 PM

We (maybe just I) got off on an AM radio tangent in the Biggest Concerns in an SHTF Situation thread. Rather than continue down the tangent in that thread, I thought a separate thread may be better.

Good AM radios are readily available, but in some the AM antennas are rather weak and only good for receiving local stations. My Panasonic RF-2400D has a pretty good AM antenna and overall is a pretty decent receiver, but other small AM radios need help. One of the sites I visited in my quest to get education on better AM antennas was/is:
AMANDX AM Loop Antenna Calculator (by Bruce Carter).

What exactly is a loop antenna??? Think of the loop windings as an inductor which provides for area to capture the AM signal. The capacitor tunes the inductor to the AM frequency of interest so that it resonates and becomes a functioning antenna. Those are my words, but the concept is really simple.

I found an appropriate (365pF) capacitor on Amazon (also available on eBay) and 18ga wire is readily available at HomeDepot; an old wooden wine crate was in the garage gathering dust ó ~14Ēx10Ē with room for 18-24 windings so that became my platform cool

According to the AMANDX calculator it should cover from ~500-2600 kHz w/ 18 windings and ~362-1900 kHz if the number of windings is increased to 24. Since the AM band is 530-1710 kHz, either will probably work. A 100í spool of wire will give me 24 turns (4í per) so I can do the higher turn count with no splices.

I may tweak the wire spacing, but for the wine-crate platform and the given capacitor, 18-24 windings seems to be a design constraint. That antenna will be for inside, Iíll use a plastic storage-crate to make another larger antenna for outside.

So how does your AM radio connect to the antenna? Induction. Place your radio next to or inside the crate, thatís it.

All that or you can just buy a Tecsun AN-200 AM... Radio Antenna
The Kaito AN200 AM Medium Wave Loop Antenna is a passive (NO power requirements) radiant device that works by either placing it next to the portable radio's internal AM rod antenna or by connecting it to larger desktop radios that have AM antenna terminals by using the included 1/8" to bare wire cable.
The best location to get the signal better is in the center of the beautiful ring...

ó Itís about learning.
Posted by: Russ

Re: AM Radio (antennas) - 10/17/19 05:11 PM

Tweaking the wire spacing does very little if anything and itís easier to simply wrap the wire with zero gap rather than a specific spacing. The wire insulation provides for the separation of the copper conductors, so spacing will be ~0.1Ē. Iím going with 18 windings (433-2389 kHz) in the loop which will cover about 1.8Ē of the 6Ē available. After the loop antenna is tested and checks good, Iíll cover it with a veneer to (1) protect the loop and (2) dress up the box to make it look nice.

SInce the antenna is totally passive, it doesnít need to be anywhere near the 120VAC 60 Hz power which is the primary source of AM static & noise.

Next, I need to study small footprint SW antennas.
Posted by: Russ

Re: AM Radio (antennas) - 10/17/19 11:46 PM

For completeness, hereís a (rather long) article on AM Loop Antennas which is worth skimming, good reference with more links.
Posted by: LesSnyder

Re: AM Radio (antennas) - 10/18/19 03:16 AM

Russ... enjoyed your comment on a search for small footprint antennas... I was fortunate to have this large footprint AN/FLR-9 antenna tasked to my targets in 1972-73 ... 6922nd Security Group, Clark AFB, Philippines.. I am honored to have worked with the best Morse intercept Operators, Asian Linguists, and Radio Traffic Analysts;attredirects=0
Posted by: Russ

Re: AM Radio (antennas) - 10/18/19 03:49 AM

Nice, not exactly man-portable, Wullenweber Array IIRC. wink
Posted by: LesSnyder

Re: AM Radio (antennas) - 10/18/19 01:56 PM

yes...the structure in the foreground was the USAF jungle survival school