Sunday, 27 November 2016

How to build a homemade loop for SWL

I have decided to post up some simple instructions for a really easy SWL loop that I use everyday as my main SWL aerial with my Tecsun PL660. It is especially useful if you live in a noisy area or house (RF noise, that is ha ha). I have suffered from RFi noise for years living in an urban environment and didn't have the money to consider a commercial loop. I also wanted to try and build something for myself. I get a lot of pleasure out of using something I've built myself. For myself, I really wanted to try a homemade loop but had very little confidence in my own abilities and didn't really know where to start. Even a lot of the websites I looked at presumed a level of competence and experience way beyond where I actually was. So hope this helps and if you have any questions, please feel free to ask via the comments.

You need a capacitor. Either the little square ones that come out of AM portable radios or a vintage type one with vanes that open and close. Either are available on ebay. For my loop I use an AM one I removed from a broken portable radio, but I've also used the type with vanes.

Once you have chosen your capacitor you need to connect a loop of wire across the terminals. I use a loop 35cm in diameter of insulated wire, but for listening it doesn't really matter what type of wire you use. Connect it to the capacitor like this:

If you decide on the AM radio-type capacitor like me, you may have to experiment a little to determine which terminals to connect the loop of wire to. I used a big metal tag on the left and a similar big tag on the right. Use crocodile clips to test the aerial once you've built the pick up loop and then solder once you have determined which ones tune the aerial across your desired range of frequencies.

So you now have something like this (though for now only connected using croc clips):

Next you need to build the pick up loop. There is no physical connection between the pick up loop and the main loop. I didn't understand this when I first tried to build mine. The pick up loop just sits inside the main loop and picks up the received and tuned signal via INDUCTANCE (ie its physical proximity to the main loop). Again you can use any type of wire. I use the braid only of a piece of coax. I read that the pick up loop should be 20% of the main loop, but this looked ridiculously small when my main loop was only 35cm so I settled on 14cm diameter and it worked just as well. Connect one end of this smaller loop to the center conductor of a piece of RG58 coax and the other end of this smaller loop to the braid. I actually don't use coax at all and bought a small 1.5m length of wire on ebay with bare wire on one end and a 3.5mm plug on the other (search for "3.5mm plug to bare wires"on ebay). I've also used speaker wire with a 3.5mm plug soldered on the end.

That, basically, is it. Find a nice project box, put a few stickers on it, and you're away. I kept the shapde of a loop by putting my 35cm diameter loop inside a section of grey insulation tube, the type used to keep pipes warm. It's dead cheap and looks cool, but is tricky to glue to the side of the box. I used a hot glue gun. I've also used plastic water pipe as the main loop. Use anything that keeps your loop in a more or less loop-like shape. A small hoop. A small wooden square-shaped frame.

Depending on the type of capacitor you've used, you probably won't get a huge tuning range from a single capacitor, unless you use a 750 to 1000pF variable capacitor. I used a 1000pF variable capacitor with reduction drive that I got off ebay and it covered around 3mhz fright up to 30mhz! But my AM radio cap only tunes 7mhz upwards, so to get down to 5mhz I've added a small 220pF ceramic capacitor and put a switch in the wiring to cover both the lower end and the upper ends of the band. DON'T PANIC!!! This sounds complicated but it is not. These ceramic capacitors are cheap on ebay and if you only need to drop a couple of MHz down in frequency a 200-300pF one will be fine. The more capacitance you add, the lower it will go. I'm guessing that 500pF might take you down from 7mhz to 4mhz. Maybe 3mhz if you're lucky.

So, you need to buy a 200 to 500pF capacitor and a little switch from either ebay or Maplins. I removed mine from a broken radio. You wire it up as follows:

The two rows of three squares are the little terminals on the back of the switch. In this set-up, when you slide the switch to the LEFT my loop tunes approx 5MHZ to 7MHZ as the little 220pF capacitor is inline. When you slide it to the RIGHT, the capacitor is out of line and I get the normal loop tuning range from 7MHZ to 22MHZ.

So I hope this helps a little, and as I said at the beginning, if you want any help or assistance, please feel free to email me via my email on QRZ,COM or via the comments on the blog. It is an easy project. The hardest thing is finding the confidence in yourself to have a bash. I had school teachers that inspired precious little of this in me and I left school thinking I was useless. It's taken 30 years to realise I was wrong!!!!!

My finished loop after dozens of attempts and several years to get it more neat and tidy|:

Saturday, 26 November 2016

Listening to North West Africa on 8903 khz

I have always loved this area of Africa. I remember Michael Palin's "Sahara" series and the vast oceans of sand and the exotic cultures and people that live here. So I've always enjoyed listening for flights crossing
the area.

In recent times, the signals on 8894khz have all but disappeared, I suppose as the VHF infrastructure improves. And when I do occasionally here someone call Algiers, the Algiers controller no longer booms in loud and clear but is weak and unreadable. A similar situation with Tripoli on 11300 years ago being very strong - almost ridiculously slow: I remember cheaper radios would be overloaded by the signal!

Anyway, in recent days I've heard aircraft on 8903 again, after a long gap. Perhaps reception at the new QTH is helping, as I am so close to the sea. Anyway, I have heard aircraft calling Niamey, Kinshasa, and Lubumbashi. Niamey is the main one active and readable for me and here are a few of my recent catches:

22NOV16 8903 khz USB:
1752 Kenyan 534 Nairobi - Lagos and clg Kinshasa
1802 maybe Manila ACC? wkg a Japan air flight?
1804 9H-FLN a Global 5000 clg Lubumbashi
1809 Tunisair 397 Tunis-Ouagadougou wkg Niamey with positions, estimates and ETA
1819 KLM589 Amsterdam-Accra wkg Niamey approaching the Niamey boundary FL380

25NOV16 8903 khz USB:
1859 Air France 860 Paris CDG to Lome wkg Niamey

I may have a listen on 11300 and 5517 for any activity from Tripoli and will report anything on the blog.                       

Wednesday, 16 November 2016

HF Logs for 6733khz

Only yesterday I was saying how I prefer not to scan HF frequencies for fear of missing the vital few bits of transmission at the beginning, and how I tend to sit for hours and hours on a single frequency. But I think, on reflection, that the reason I don't scan HF is because on my FRG100 (now sold) and my Icom 703, programming the required frequencies into the scan, deleting yesterdays, and setting up the scan itself was not the simplest and quickest of procedures.

But in this new QTH I am listening using only my Tecsun PL660 on the batteries as there is much less RFI than when using a radio on the mains. And setting up the scan you require for the day is simplicity itself. The Tecsun PL660 doesn't, of course, have a squelch. So you program in your frequencies and it scans each one in turn, stopping for 5 secs on each channel. As I am also using my homemade passive loop which requires re-tuning every time you QSY, I decided to program in 6712 for the French Air Force, and one or two military air frequencies each side, close enough to 6712khz not to require a re-tune.

Within minutes I picked up some really clear Italian voice comms on 6733khz with IDR, The Navy HQ in Rome, working "Dagger 05". The ship appeared to be giving a position report, he mentioned his operational area, and then gave a lengthy weather report:

"........visibilita 6000, mare 3, QNH 1025, temperatura 15 gradi, nuvolosita 6 ottavi (6 OKTAS) 4000 piedi"

He addressed Rome as "delta romeo" (from iDR I suppose).

If anyone reading this can offer me any help at all with the callsigns used, I would be really grateful. I presume it is "Dagger" but I have heard comms here in the past and heard what I wrote down in my logbook as "dagateisha", so I may be totally wrong. My Italian is only really basic!

The military HF frequencies interest me a great deal, but they can be tricky to ctach as days will go by when there is no training exercise taking place, and you begin to presume the frequency has become inactive until you get a great burst of activity such as I did this morning!

73 Adam

Tuesday, 15 November 2016

Algeria HF AERO

15NOV16 8894khz 0639UTC: heard HB-FLH, a Pilatus Porter, wkg Algiers with departure and arrival times & altitude. This is one of several small Swiss-registered aircraft that regularly appear on this frequency from companies like Star and Zimex Aviation that, as far as I know, bring passengers and supplies to the Algerian oilfields.

Other recent logs also include French Airforce Transport aircraft (COTAM) wkg 6712khz and a German Airforce aircraft on 6730khz.

So despite HF being used increasingly less, there are bits and pieces still left if you know where to listen. I get depressed when I see the internet listing hundreds of frequencies that really interest me, only to discover the lists are old and out-of-date, and the services stopped being active years ago. So that is mostly why I write the blog: to let other fellow aviation enthusiasts know what can still be heard. Often I will spend hours and hours monitoring a single frequency - I don't do much HF scanning as I find you miss the initial details of the transmission, and those are the juicy bits with the callsigns and names of the stations.

I know there are some interesting catches to be had using the data modes of HFDL and one of my favourites, ALE. But I don't do very much data decoding these days as I find it hurts my eyes and gives me a headache. And for me, nothing beats the sound of a pilot's voice appearing out of the ether.

73 Adam

Sunday, 13 November 2016


13Nov16 11285khz South East Asia
Using Tecsun 660 and small homebrew tuned loop:

1539 utc Flight Molinda Air 223 Kuala Lumpur to Tiruchirappalli
wkg Chennai radio with position reports for NOKRA and ASBIK

1605 utc Flight Malaysian 179 Kuala Lumpur to Colombo wk Colombo req deviation 20nm left

1609 utc Flight Molinda Air 185 Kuala Lumpur to Colombo wkg Colombo fl30 SULEN 1609 selcal chk req deviation 30nm left of track.due wx
All of the above flights were readable on just the telescopic whip however due to local electrical interference I use my homemade loop to null that out effectively and furthermore on 11 mHz the loop actually provides a slightly stronger signal whereas I have noticed on the five six and 8 Mhz AERO band the telescopic whip is slightly better but of course I do not have the option of nulling out the noise.

Monday, 7 November 2016

MEDIUM WAVE Maritime Monitoring

Not much Radio blogging this year as I have moved qth but now that the boxes are unpacked and I have been reunited with my Radio Gear and given that I am only a few feet from the sea I have started to listen to medium wave maritime stations and thought I would post a Blog of some of these logs.

06nov 1818utc 2656khz Ancona Radio wx
06nov 1838utc 1665khz Tjome Radio
06nov 2105utc 2657khz Alges Radio, Portugal wx & nav warnings
04nov 1935utc 2719khz Porto Torres Radio good sig, wx
04nov 1935utc 2680khz Cagliari radio weak, wx
01nov 1935utc 2579khz Bari visibilita buona, wx, II
01nov 2140utc 3673khz Netherlands coastguard wx EE
25oct  1935utc 2182khz RNLI lifeboat 2EQY wkg Ostend & Netherlands cg for radio check

All of the above logs were made using pl660 and homemade tuned loop.