Interesting external 'short wave' antenna.

[catman]

G'day all, I acquired this old but perfectly working old National Panasonic radio from a local Ham Radio convention some years ago.

A while back quite by accident I discovered this 'loop' antenna which apparently is the inbuilt external short wave antenna. When fully 'extended' it is actually quite effective.

Rather different to the possibly more usual telescopic whip type of shortwave antenna. How common was this antenna 'arrangement'? I suspect that the radio dates from the late 1960's or perhaps early 1970's. Any thoughts or comments? Regards, Felix (vk4fuq) aka catman.

[Electronic M]

In the tube era multi-turn shortwave loop antennas were common, but I can't say I've seen one quite like that before.

[Sandy G]

That radio looks a lot like my National Panasonic RF-5000A, which was Panny's answer to the Sony CRF-320, which I have as well. The Sony is clearly the superior set, but the Panny is much better looking...Mine has that type of antenna, too. Not very effective, IMHO.

[JBL GUY]

Hello Felix

That is a nice looking radio.

I wonder if it functions as a true loop?

It would be interesting to take a look at the schematic.

As you know, with the correct matching and electronics, small loops can function much better than one might expect.

Thanks for the information and pictures.

[catman]

G'day all, another photo from the back panel.

It looks like it is the model R-441B (D). It seems like the manufacture date was sometime in 1974 (I think), judging from another sticker in the lower right hand corner. Regards, Felix aka catman.

[radiodayz]

I've seen several of those Panasonics with the built-in shortwave loops. I don't think any other manufacturer used them (maybe Zenith on some of the Transoceanics?). There's actually a fellow in Australia who builds loops for longwave, mediumwave, and shortwave. I have one of his mediumwave loops; it works quite well. http://www.amradioantennas.com/

[wa2ise]

Would the SW loop antenna be useful to null out jammers when trying to listen to a SW station your government doesn't like (if you lived in a communist dictatorship)?

[catman]

G'day all, I was using this radio a little earlier and I'm not sure if it is connected as a true loop, however it is entirely 'untuned'.

I know of the company mentioned earlier. Most of his AM loop antennas are 'tuned loops'. I have made a few tuned loops myself for the AM broadcast band. They work well. Regards, Felix (vk4fuq) aka catman.

[JBL GUY]

Hello Felix,

Thanks for the update and for sharing the information about your radio.

So many people today do not understand the magic in hearing a signal from, and for some of us, communicating with a far away place.

While I was still in grade school I received as a present, a Realtone brand portable radio with shortwave bands.

While it was not a stellar performer, I will not forget the thrill of hearing DX shortwave signals.

Your post brought back some very pleasant memories.

[catman]

G'day mate, in a way it's a bit sad as the short wave bands are rather empty nowadays.

This evening tuning the range from about 9 Mhz to 30 MHz all I could hear well were the time signal stations on 10 and 15 MHz and Radio Australia around the 31, 25, 19 and 16 metre bands.

I miss the old days of stations everywhere on the short wave bands. Regards, Felix (vk4fuq) aka catman.

[dtvmcdonald]

I've tried several (passive) loop antenna designs for my RCA 121 superhet radio (has RF stage), both broadcast and SW.

The Broadcast one is a 15 inch square with 14 turns and a tuning capacitor;
the output is at a tap one turn from ground. This has a Q of about 100.

I tried several SW loops. The best was a 6 foot diameter single
turn tuned with a 3-50 pF capacitor. The feed was a 15 inch loop at the
opposite side from the capacitor (inconvenient)!

The broadcast one is as good as a 30 foot indoor wire. With it the
radio provides passable room volume on atmospheric static and
the rejection of CFL noise is excellent.

The SW one is nowhere near as good as the 30 foot indoor wire.
But it is good enough to put the atmospheric static above
the noise floor of the set even at 16 MHz. The static, and hence the
limit to weak signal reception, is weak enough that you need a very quiet
room to use it for DX. Actually it turns out that putting a 1.5 volt battery
in the AGC line to make it less negative give a respectable volume. An extra
audio stage would make it work perfectly.
I'm surprised that no radio maker added an extra audio stage, or added
a step-up transformer between the first audio and the output. This
latter would have been very cheap in the olden days.

Edit: I tried a new SW one using 1/4 inch copper tubing for the loops
instead of wire. It worked quite bit better, higher signal and higher Q.
The Q is so high it is very hard to tune. It went lower in
frequency with a 250 pF capacitor. I tried placing the 18 inch diameter pickup loop
at various places around the 6 foot one and found that location made little
difference.

[boora2]

Some of the first portable tv sets color or black and white used a loop antenna for uhf in Australia,the imported Toshibas,and decca gypsy,come to mind.