Active antenna experiment.

Having visitors this week end put a limit to my radio activities, but one thing got done.

I built (did not take that long) a small balanced amplifier with a TL592 IC. The aim is using it with small loops and ferrite antennas.

The amplifier can be found at Low Frequency Antennas , I made it for a bit higher gain and with a manual tuning capacitor in stead of the varicap, but essentially everything is as in the circuit diagram.

Going through resonance on 80m and 160m the noise increases by 20 - 30dB, so the noise figure and amplification looks good. It looks like the amplifier will support even smaller antennas than my 80-160m tunable loop.

Further experiments with the amp. should include smaller loop/frames and ferrite antennas. It could be interesting to see if the small (50 - 60mm long) ferrite antennas from small transistor radios will work in the indoor noisy environment, or even what they will do outdoors in the open (less noise)

A bit of 500kHz experimentation

The new cardboard box frame antenna with better wire turns out to be a bit better. A few dB increase of S/N has been gained.

The loop was at first connected to the HF-3 receiver, and gave some WSPR spots from local stations like PA0A, PA3EGO (also seen with QRSS) and PA3FNY, with relatively good signals if considerably lower than Joachim gets with his Octaplumb. Also G4JNT during night time and one or two other spots from G stations. All in all not very impressive, but not too bad for an antenna inside the noise field of the apartment. Also every night DI2AM with QRSS, and occasionally a good signal from OK0EMW.

A test with the ATS909 receiver, using just the built-in ferrite antenna gave surprisingly good results, almost as good as the cardboard loop with the HF-3, with DI2AM in every evening.

Test with the FT-817 gave a marginal improvement over the HF-3, maybe 1 - 2 dB.

Test with a FRG-100 receiver showed that the receiver is considerably more sensitive than the FT-817, but due to "antenna noise" (apartment noise) the improvement was again marginal, 1 - 2 dB.

The antenna has now been moved upstairs, still indoors, and another 1 - 2 dB has been gained. interesting to see how much signals will come from the G stations now.

An improved loop for outdoor mounting, like Joachim's Octaplumb will be built here, and some tests with larger transmit antennas are in the plans. Well, and a TX, too, probably beginning with some 50 - 100 mW, so ERP will be in the microwatt range.

This week I am having a visit from a friend staying over, so not much time for building activities, but after that it should go on.

I still have some experimentation on the Rockmites and a Warbler, so more than enough to do here.

Also some experiments with the TL592 amplifier for active antennas (LF,MF,HF) is in the thoughts here, such as variations on the antenna from this site

DI2AM reception on 505 kHz

The 500 kHz grabber is now set to two narrow frequency ranges, the "WSPR segment" and 100Hz around the frequency of DI2AM.

DI2AM reception seems to be there essentially all the time after sunset, albeit with some (expected) QSB, and WSPR signals coming and going.





Nice result with a "cheapo" frame antenna wound on a cardboard box 35x40 cm small.

A new somewhat bigger frame antenna (more than 70x70cm) will be made some time, but that will have to wait.

In the week end the construction of the 500 kHz TX should begin

160m - 80m Experimental Loop

Yet another receive loop is born.

The construction is similar to the first 500 kHz loop, i.e. cardboard box loop, but made with Litz wire and with only 6 turns.

The calculation of resonance frequency found here indicates a frequency range covering the whole of the 160m and 80m band, and this looks like what I have.

The coupling is made with a further full loop, and it looks like that creates a too hard coupling to the antenna (not really unexpected), making the antenna rather broadband.

Later this week some experimentation on the coupling loop size is in the planning.

Better antennas for LF/MF

In order to make loop/frame antennas with higher Q for the low bands (160m, 600m, 2.2km) I have ordered some Litz Wire from across the "pond".

It will be interesting to see how much improvement I can get from this.

"eBay" , of course. It can be a dangerous place, but it is our last, best hope for strange raw materials.

500kHz antenna connected to the HF-3

The antenna is now connected to the HF-3 and receiving there. DI2AM is visible, if not too strong. Some WSPR signals are easily visible, with the WSPR program they should decode nicely.

For now I will leave it running, and in the week end the 500 kHz system could come on the TVEPG grabber page. no time now, and tomorrow some non-radio activity.

Still the signals are not all too strong, so a better antenna is required here.

The noise levels, however seem very low here.

"Progress" report 500kHz RX antenna

Well - let us say - the antenna tunes down to 500 kHz, but the output looks lower than I get from the ferrite antenna of the ATS-909. The S/N, however sounds like it is better.

The source of the lower output ? I am not sure, but suspect the small size of the loop contributes, and perhaps the coupling winding is not enough with a single turn. further tests are needed.

OK - this antenna is rather small and uses standard hookup wire, so the highest efficiency is not to be expected. a somewhat larger antenna, say 1x1 m made from Litz wire should provide substantially better results.

The first test was with a "dual gang" variable capacitor, but with only one plate set used. of course the hand capacity detunes the antenna so it is essentially untuneable.

SO the second test was with both plate sets, and now we are getting there. because the hand is at the center of the capacitor, no detuning or hand capacity effect is noticeable.

With the 25 windings, the antenna tunes down to just under 500 kHz, so the antenna is a qualified success.

The ATS 909 seems to have a rather good sensitivity on MW, so it is a bit difficult to fully judge the efficiency and usability of the antenna.

The tuning is not *very* sharp, but with a decent maximum at resonance.

The next test should be connecting the antenna to the HF-3 RX which should have a very high sensitivity on 500 kHz. Oh, now for soldering another connector to the cable and see what it will do.

Another solution to the low output could be to build an amplifier, but that sort of defeats the purpose of a 'simple antenna'.

More room for experimentation.

500 kHz Receiving Antenna in the Make.

I have been looking into the options for receiving amateur signals on the 600m band (500 kHz). Since I live in an apartment size does matter, so looking for a small sized antenna I looked around and found this article from VK2ZAY , showing a simple 'frame antenna' made with a cardboard box.

Being close to all kinds of noise sources I think the loop is probably the best option for a receiving antenna on such a low frequency.

Since I intend to use the antenna indoors the support material does not matter much.

The box measures are on the small side - 35x40 cm (14x16 inches if you like) - but as a proof of concept I have put 25 windings with taps at 15 and 20 windings, as well as a single winding coupling loop.

Now I will be looking in my junk box to find a suitable variable capacitor to complete the project (this may take some time).

If this works out to my satisfaction I will try out frame antennas for 80m, 160m and 2.2km as well, at some time.

Since there seems to be an experimental license available here in The Netherlands I may even try to put out a 600m signal, yes, I am considering joining the experimental group. The decision, however, has to be made soon before the opportunity expires.

Non ? Active loop antennas

I found some Chinese "active loop antennas" on eBay the other day, the price
was reasonable at $25, so I decided that it was worth the risk trying it out.

Since it had the brand name "Degen" (type "31MS" - guess that would mean MW and SW) Joachim and I joked about it being a "degenerative" antenna.

I picked the antenna up at the post office today, and gave it a brief try, and it looks like it lives up to its name and that the joke was not really a joke at all.

The first thing that happened was that a suction cup for mounting the antenna on a window would not stick to any window at all, poor manufacture quality, even for a Chinese product. It did not bode well.

On MW the S/N is lower on the Degen than on the built-in ferrite antenna. on a part of shortwave it looks like it has some minor gain on frequencies in the 5 - 15 MHz range, but its effectiveness was not easily detectable.

I may have to try it during daytime, but I am not optimistic.

If you see it for sale, it does NOT have my recommendation. I may be able to use parts of it for experiments, but I doubt it will do much for me.

In any case I intend to take it apart and see how they managed to do so little.

Conclusion : Cheap antenna with cheap performance.

FAIL.

half hour antenna for satellite reception

I was growing tired of having poor reception of the transmissions from ISS on 145.800/825 and 143.625 MHz, so decided for a quick ground plane antenna. What to do for a quick antenna ?

Here we go :

1) use a piece of coax, strip about 53 cm of the shield off
2) connect 2 pieces of (insulated) wire about the same length to the shield connection
3) insulate with duct tape for a quick weather protection (will not hold long, but this is a temporary setup)
4) string the thing up between the clothesline and the balcony railing
5) pull the cable through the wall/door/window
6) add connector indoors to the radio and connect to radio
7) done

Results receiving ISS were better than using mu uhf-satcom log periodic array (no real surprise there)

I still need a better antenna/antenna position (poor reception when the ISS signal has to go through the buildin), and since I have some noise, so more to do.

Probably a 2m antenna with preamp (cable length) in the dormer.