Category Archives: Antennas

“G8JNJ Reverse Engineers and Reviews the MLA-30”

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Many thanks to SWLing Post contributor, Paul, who shares the following story from the RTL-SDR.com blog:

Last month we posted a collection of reviews about the MLA-30 which is a budget magnetic loop antenna designed for receiving HF signals. The overall consensus from the reviews was that it worked decently for the price, but of course could never live up to the high end loops that cost hundreds of dollars.

Recently Martin (G8JNJ) reverse engineered the active circuit used on the loop from photos taken by M0LMK and has made some observations on it’s performance, noting that it’s design isn’t very good. First he notes that the amplifier chip is a Texas TL592B two stage video amplifier which isn’t that great for this application. His measurements show an OIP3 of 20dBm, a P1 saturation of -3dBm and a noise figure of 12dB.

Of interest, he explains that the creator of this loop has designed it poorly as the impedance match of the loop to low pass filter is very wrong, resulting in a very poor amplitude/frequency response. He shows how the response can be improved with a few termination resistors, but is still not great.[…]

Click here to read the full article at RTL-SDR.com.

 

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Radio World: Construct an EAS Receive Loop Antenna

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The completed antenna, showing the F-connector on the tee box. (Source: Radio World)

Many thanks to SWLing Post contributor, Kris Partridge, who shares the following antenna construction article from Radio World:

Ken Beckwith is a field engineer with EMF based in Nebraska. Being a hands-on engineer, Ken has done his share of construction over the years. One of his projects was the construction of an octagonal-shaped AM loop EAS antenna using PVC pipe.

[…]The antenna has a broad coverage angle with a deep null when the antenna is broadside to the signal. Aim the “edge” of the loop toward the AM station you want to receive. The strongest signal will be received when the antenna end or edge is pointing to the signal source. The antenna can be mounted on a mast with U-bolts, hose clamps or whatever else works.

Here’s the construction parts list:

A 10-foot length of 3/4-inch diameter, schedule 40 PVC conduit cut into the following lengths:

2 – 4-inch
1 – 2-inch
1 – 2-1/4-inch
2 – 2-1/8-inch
6 – 9-1/2-inch
1 – 23-1/4-inch

Whatever is left over can be discarded, but before making your cuts, cut the flared end off, so all cuts are even.

1 –  3/4-inch 90 degree elbow
2 – 3/4-inch tee
8 – 3/4-inch 45 degree elbows
1 – 3/4-inch cap
1 – 3/4-inch tee box, plastic, with weatherproof gasket
1 – 7-foot piece of Belden 8777 or other three-pair shielded cable
3 – 7-foot single-pair shielded cables can substitute for Belden 8777
PVC primer and cement
Wire nuts or other connectors
1 – 3/8-inch ring terminal
F connector barrel with nut

[…]

Click here to read the article which contains step-by-step instructions.

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Marty needs advice as he builds a passive magnetic loop antenna

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Many thanks to SWLing Post contributor, Marty Kraft, who asked that I share the following question with our community:

I’m still working on a receive-only passive hula loop magnetic antenna for my Tecsun PL-660.

After viewing thousands of YouTube videos (LOL), I built the PVC-pipe structure [you can see in the photo below].

But I need some tech help to finish…

The antenna is 90 inches tall; large loop diameter is 40 inches; and small loop diameter is 17 inches. The wiring is 14 gauge braided.

I plan to put the antenna outside on the porch. Then I’ll run coax from the small loop to the receiver inside and use a 365 pF air variable capacitor to tune the large loop.

My first question is, what’s the best coax to use for the 10-ft run from the small loop to the radio inside? Second, will that 365 pF cap tune the entire 3-30 MHz range?

It’s hot here in Louisiana, so I’d really like to tune the capacitor from inside my apartment, also using coax to connect the cap to the large loop. Will that work? Or does the cap have to connect directly to the large loop?

Any other tips or suggestions? Thanks for the help!

Post Readers: If you have any helpful advice for Marty, please comment!

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David reviews and compares the MLA-30 magnetic loop antenna

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Many thanks to SWLing Post contributor, David Day (N1DAY), who has completed a thorough review of the MLA-30 loop antenna. In this review, he compares the MLA to the Wellbrook ALA1530-LF and a 30 foot square ground loop antenna.

In short, he finds that the MLA-30 performs fairly well on the AM broadcast/mediumwave band, but can’t compete with the Wellbrook otherwise–especially in terms of noise floor. David also noted that “the MLA-30 had a very serious issue with IMD and in some cases, stations that were clearly heard with both the Wellbrook and the ground loop were totally obliterated by IMD when switching to the MLA-30.”.

Click here to read David’s full review on his blog, Ham Signal. 

Click here to view the MLA-30 on eBay.

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Swiss Army Knife FM antenna

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Many thanks to SWLing Post contributor, Balázs Kovács, who shares the following video of a Swiss Army knife and tweezers being used as FM antennas:

Click here to view on YouTube.

Thanks for sharing this, Balázs. The video actually makes a good point: it takes so little to make an effective FM antenna to receive local stations. I’ve been with repair technicians when working on radios They’ll often use their precision screwdriver as an antenna to test the receiver before reassembly.

I also carry a couple cheap instrumentation patch cord with alligator clips on both ends to act as a short antenna or antenna extension when needed. Honestly, It’s amazing how often I reach for them!

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Ron is impressed with the PK Loop Mini (A-LOOP-MTAM)

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Many thanks to SWLing Post contributor, Ron, who shares the following review of the PK Loop Mini (A-LOOP-MTAM):

Standard PK Loose-Coupled Loops (the “A” series) are 14 inches in diameter…they are
for use with a receiver having a built-in ferrite bar antenna.

Don’t think they’re not capable of serious DX…a few years ago a friend in Texas
snagged and recorded France Inter (162 kHz) on a 14 inch standard PK LW
loop using a Sony 7600GR.

But this is about the PK Mini 10 inch loop for Medium Wave (there are none for
other ranges).

The build quality is superb as with all PK loops. The band has two ranges: 525 to
710 and 710 to about 1720 kHz. Paul Karlstrand uses a unique design consisting
of flat computer cable and a custom made circuit board to connect the turns
end-to-end.

The low end simply switches in a fixed capacitor across the variable to lower the
frequency.

The Mini has 25% less sensitivity than the standard 14 inch loop according to the website.
Currently it can be had for $66 USD delivered to your door from Melbourne…this one
was ordered on a Monday and showed up a week later,which is outstanding considering
it had to clear customs in NYC.

Performance is virtually identical with the Tecsun or Terk loops, which are 9 inch loops.
So why buy a PK?

You get what you pay for, or not…the PK is fairly robust compared to the Tecsun or Terk.
It’s made to last and it’s a PK Loop.

Here are some links for comparison purposes:

If you wish to enhance your loop try co-coupling it to your receiver with a Q-Stick :

http://dxtools.com/QStick.htm

Thank you, Ron, for sharing your experience with the PK Loop Mini. It certainly sounds like an excellent option for travelers and, like you, I agree that the construction quality is superb!

Click here to check out the PK Loop website.

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