Monday, 30 April 2012

LF Loop

As promised, here is a photo of the LF loop:

As you can see, it is not the sexiest antenna in the world, and I have to admit to being a bit of a commercial-product-addict in past years. But since becoming a "ham" I have enjoyed tinkering around with homebrew antennas using bits of recycled timber and old radios. There is also the added enjoyment that, when you do receive a nice signal, it is done so on something you have put together by your own hands. Now I'm getting older, I enjoy that feeling!

On the above loop, I heard Paris Orly NDB "ORW" on 402.0khz this morning, my first signal from the French capital.

I have also ordered Edward Noll's book "25 Simple MW and Tropical Band Antennas" as I loved that series of Mr Nol's books as a youngster. So I might try my hand at a tropical band antenna next.

I also quite fancy having a bash at a larger LF loop. My experiments with HF loops have shown me that the size is not at all critical, and I have come down from 1m diamater to barely 40cm diameter with no noticeable loss of received signal. But my instinct tells me a larger LF loop might make all the difference in pulling in these very weak NDB signals from around NW Europe.

Sunday, 29 April 2012

LW NDB Beacons

It has been raining much of the week and I have spent the last few days with a heavy cold, so as going out wasn't going to be an option, I spent the time building a loop antenna for long wave. I used an old MW prototype and simply extended the wire from 13 turns to about 25. In order to cover both the LF broadcast band and the NDB beacon band, I needed to add a switch that kicked in an extra 940pF of capacitance to reach right down to 153 khz and allow me to receive Deutschlandfunk and France Inter, the latter being a station I am growing to really like.

 The MRV aero NDB at Merville (Calonne), France
which I have logged several times from my QTH
here in Torquay.

My first few hours of beacon experimenting were disappointing and I was barely able to receive the "EX" NDB here at Exeter airport (only 19 miles away!). But I soon realized that despite the DX394 being VERY sensitive on the LW broadcast band and both the MW broadcast and marine bands, it is all but useless on the bit inbetween ie from 250khz to 500khz. As soon as I swapped over to my Sony SW7600GR things improved enormously. I inductively coupled the Sony with the loop by simply sitting the 7600GR inside the loop with no direct connection to the radio, and this is working wonderfully.

I have logged dozens of beacons from as far afield as Belgium and Northern France, with my best "DX" so far being the Mackel NDB (MAK) near Ghent at a daytime distance of 311 miles. Considering these beacons are low power in the 25 watt range, I think this is great.

I am too tired to post a photo of the loop tonight, but when and if the sun comes out I shall try and take a nice shot of it now that I have spent the afternoon tidying it up and revamping it a bit. At first I simply added the extra turns needed for the LW band over the top of the windings already on it for MW. But after I unwound that mess and did it properly the capacitance dropped significantly requiring more turns and yet still extending the coverage significantly. It now tunes 150-200khz with the extra  940pF switched in, and 230 to 860khz with it switched out.

In order to make use of the gear I already had in the shack and not buy new stuff, I tune both sections with both an AM radio capacitor salvaged from an old radio, and a vintage radio capacitor brought for 20p from the Wooton Bassett Vintage Radio Rally last year.

So altogether the loop cost me, ahhh let me see, 20p!!

Wednesday, 25 April 2012

Loop for Medium Wave

I have been a member for the British DX Club for a number of years now, and after reading the medium wave sections by Tony Rogers and receiving some friendly emails from him about the MW aspect of the hobby I decided to give it a bash. Having been mightily impressed by the performance of my homemade HF loops that I use for listening and transmitting QRP signals on amateur radio, I decided to build a loop for medium wave.
This one is only 10 inches across, but performs just as well as the proto-type I built which was double that size. In fact, recently I have been experimenting with reducing loop sizes, and my HF receiving loop has been reduced in diameter from over one meter to a mere 40cm with no noticeable drop in signal.

The Medium Wave broadcast loop sits on a small cake decorating turner that I bought for 50p from a church sale and does the job perfectly. It is tuned using an old vintage radio capacitor and covers about 580 to 1600khz.

I use this loop with my Realsitic DX394 as that radio, despite it's low price, is a really terrific performer on MW (both Maritime and Broadcast bands). It may not have selectable bandwidths like the Tecsun PL310, and there is no sync detector as on my Sony SW7600GR. But what it lacks in features it more than makes up for in sensitivity, and weak MW utility signals in the maritime band are way more readable than on my other sets.

I love rotating the loop and hearing signals peak. And it still seems like magic to me when I discover a weak signal present in the nulls of stronger ones. 

I have just ordered an MVAM109 varactor diode from the USA for £5 incl postage as I have read that with a 9 volt battery I can vary the capacitance of the diode from 30pF to 450pF using a variable resistor. The idea is to run 30 meters of wire from the shack to the summer house where my outside loops are located and use the varactor diode to tune either my HF or MW loop from INSIDE the shack. At the moment, if I am using my outside loops, I have to run down to the summer house every time I want to change frequency, which is a bit inconvenient!

Monday, 2 April 2012

AN124 crosses the Sahara

I had a great catch on 8894 khz on saturday 31st March: one of Ukrianian outsize aircargo operator Antonov Design Bureau's Antonov AN124s checked in as he crossed the Algerian coast southbound at 31,000ft. A quick internet search and I came across a cool website called flightaware which not only located the flight, but showed the actual flight plan as well. The callsign was ADB1262 and his route was from East Midlands, UK EGNX to Malabo FGSL.