Re: Connecting the Tecsun PL-360 to a large air-core loop


It's only 11 turns spread over about six inches wide. Matching the inductance sounds like a very good idea, but I am not sure I'd want any more gain! All previous attempts were bothered by that white noise blocking everything to my west, which IS almost everything domestic from Connecticut. If that does not return, then I will be even more interested in winding both MW and LW air core loops.

Interesting Gary's ferrite never heard the white noise interference.

My four foot loop overloaded the PL-360,and received images on LW and the inductance is way too high as well.

My 2 foot loop is a sorry looking thing. I wound it with wire reclaimed from a motor, which is not straight and parallel. It was just a quick prototype. It is a much handier size than the 4 footer!

I did not notice overloading on strong stations, but I was looking for new catches, so I only tuned in weak signals.


--- In ultralightdx@..., "dhsatyadhana" <satya@...> wrote:

Hey Farmerik:

Good to hear that your PL-360 is not overloading. I have several 50 kw stations within 10-15 miles, plus two 5-10 kw stations only 3 miles away, so my location is probably the extreme. If you have a little more breathing room, perhaps you can continue to rake 'em with your 2 foot loop!

I would be curious to know if you've determined the inductance of your 2-foot loop - is it around 350 uH? Per:
a 24-inch loop with a 5-inch coil depth should have about 18 turns. If your 2-footer is wound so that it resonates over the whole band with a tuning capacitor, you're probably looking at only about 250 uH, or about 15 turns. So, you may be able to throw some more wire on to get the inductance up to where the PL-360 likes it, and even more gain!

Kevin S
Bainbridge Island, WA

--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

I tried my 2 foot air core loop again tonight, and the white noise blocking my reception to the west is gone at the moment. I found a good signal on AM 620, and it turned out to be WVMT from Burlington VT. That is a 5kW I don't recall hearing here before, but I get it when I am in Northern VT. So a 2 foot loop may not be too large for the PL-360. I do have to shut off my CRT computer monitors, and I don't have any local stations to worry about. I tried AM 650 WSM, but just got noise on that frequency. Also a pretty steady signal on AM 540, but it's all in Spanish, so I wouldn't be able to ID it easily. - FARMERIK

--- In ultralightdx@..., D1028Gary@ wrote:

Hi Kevin (and Stephen),

Thanks for sharing the results of your PL-360 air core loop
experimentation, and thanks again for your positive comments on the 7.5" plug-in

Regarding the overloading issue with air core loops directly connected to
the PL-360 (or other Ultralights), my own experience has been very similar
to yours. Inductive coupling to the large PVC loops had always provided
satisfactory results with the new DSP radios, and avoided any RF overloads from
local pests. As you have also documented in your excellent tuned passive
loop articles, the extra tuned circuit in the Crate Loop helps for filter
out RF overloads from local pests, and provides additional selectivity to
enhance DX reception. With the Crate Loop or PVC Loop tuning capacitor
optimized on a DX station's frequency, the splatter and spurious signals from
local pest stations is significantly reduced. From actual DXing experience I'm
sure that we would both agree that this extra tuned circuit is not a
hindrance-- it's actually a great advantage.

Probably the easiest way to understand the performance challenges in
creating Ultralight radio antennas is to remember that all designs have a
tradeoff in portability, gain, and size. The very best designs have good
performance in all three aspects, although this a subjective judgement. The 7.5"
plug-in loopstick was designed to offer good portability and gain with
reasonable size (although some would dispute that last point :-) Your Crate Loop
might provide more gain with slightly less portability, and a 9' PVC loop
would provide massive gain with almost no portability. Each DXer needs to
decide what the objectives are, and one design certainly won't work for

73, Gary DeBock (in Puyallup, WA)

In a message dated 5/12/2010 10:06:21 P.M. Pacific Daylight Time,
satya@ writes:

Hi all:

Inspired by the success of the 7.5" plug-in ferrite that Gary has
produced, I decided to see what the performance of the PL-360 would be using a
large air-core loop jacked directly in. I have an 18x32 inch PVC frame with 19
turns of wire, spaced over about a 10-inch coil depth. It measures out to
just over 350 uH, matching the inductance of Gary's ferrite rig. I simply
connected both of the coils leads to a 1/8" plug, and connected it to the
jack on the PL-360.

Using stable daytime targets, the first was a TIS-type station on 540. The
7.5" ferrite had it at 34 db signal and 6 db SNR. The air-core clocked in
at 56 db signal and 24 db SNR, and it really sounded like a huge boost as
well! I felt my pulse quicken just a bit...

Alas, being in an urban area near several powerful broadcasters, the
air-core started having problems, apparently with overloading, as I got into the
MW band. Tuning up and down the dial, I often had the dreaded "50-00"
reading on the PL-360, which I interpret to mean that it has so much signal
that it is desensitized/swamped. DX targets could often be heard, but at much
reduced volume. The ferrite, on the other hand, was still behaving well and
receiving stations as it should.

At night, everything was still at or above 50 SNR with the air-core loop,
even on fairly vacant channels, except again at the far end of the band,
away from my various strong locals. It wasn't quite as bad as when my locals
were on day patterns, but still quite swamped.

I had similar results when I jacked in a large air-core loop to the Eton
e100 - it was simply too much, and near locals the desensitizing was
significant, although I dare say the PL-360 is having an even tougher time.

So, perhaps there is a limit to what the PL-360 can accept directly from a
broadband source, at least in an urban area. I know that I cannot plug and
untuned active whip or a Super Loop/Wellbrook FLG-100 combination in,
either - simply too much input from strong locals. Obviously, based on Guy
Atkins' 18" ferrite experiment, at least that amount of signal is acceptable -
maybe there is something about ferrites (reduced stray capacitance, etc.)
that also is a factor? At any rate, those wanting to plug an air-core loop
straight into a PL-360 had better live outside an urban area!

Kevin S
Bainbridge Island, WA

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