Just an update... It's been a prolific few days since I last posted! I got some help from a few radio/HAM YouTubers and received a few email replies from some folks who built antennas. I will post what I can here and then probably another post to add more photos later. Here is one of the articles in particular that I followed closely to calculate and build a loop antenna for LW range:
https://www.randombio.com/loopantenna.htmlI have also attached an EXCEL spreadsheet I put together to help calculate the curves and figure out properties of various size loop antennas. I decided to go for a small antenna at this point due to storage/portability and not to upset the wife too much.
The dimensions are as follows... it is 26 cm diameter square, and 22 cm deep, with about 42 turns using 24 AWG stranded wire. This uses up about 43 m of wire, or 143 feet. I built the frame out of spare wood and dowels I had sitting around. I notched the dowels (made grooves) about 0.5cm apart so the windings of wire would sit in the grooves and not slide around as much:
Here it is with a few measurements:
Next I needed to plug all the numbers in and figure out what kind of tuning range capacitance I will need to get from about 153 to 513 (the LW tuning range of my Tecsun). Here is a graph showing this using the EXCEL spreadsheet I attached:
You will notice in the graph that I have a "meas" and "calc" for pF. That's because I had a theoretical inductance based on the equations for a loop antenna from that previous article, and I also measured the inductance using one of those cheap LCR meters I had around. It was actually not too far off, I was surprised:
So based on the calculations I needed to be able to vary my capacitance from about 200 pF to about 2500 pF. Not having a convenient source nor the budget to get a proper broadcast gang air dielectric variable capacitor, I decided to use a bunch of trimmers from the local electronics shop and switches to make something that I could tune into that wide range of capacitance. I bought a prototype "Schmart" board and tried to figure out how to use it, as this was MY FIRST TIME prototyping on a PCB!!! (I always cobbled stuff together before on a breadboard).
Here's what I was thinking to do:
So with both switches OFF (at the far right) and the trimmers all set to their lowest (8, 15, 15, 15), I have about 53 pF. The calculations also showed I have a distributed capacitance in the loop of 15 pF, so now I'm up to about 68 pF. So I figured if I add a 151 pF cap (the beige colored cap seen below) it will set the "floor" base capacitance to 219 pF.
Now, when I am playing around with the trimmers I can go up to a maximum of 160 pF on the 3 larger green trimmers, and 40 pF on the smaller white one. So that gives me a range of about 520 pF of variability in the trimmers. So with all trimmers to full, I get up to 686 pF without invoking any of the "switchable" caps. So far so good?
Now, I want to go into the next range, I dial all my trimmers back to the lowest values, switch in my 561 pF cap (the single blue one in the middle and you can see one of the switches is lined up with it), and now I am at 780 pF and can trim up to 1247 pF. Unfortunately this means I have a "dead spot" between 686 pF and 780 pF. I would need to add another trimmer in here to bridge the "gap" between my ranges. Either that or make the jump to the next range smaller (instead of 561 pF, I can get 2x221 pF or 442 pF jump). Either way, I would need components I didn't have. I can always modify later. Adding a trimmer (another 40-160 pF) in parallel to the circuit would solve this problem if I need, I would just lower the "base" floor cap down so compensate for the extra 40 pF on the lowest end of the newly added trimmer.
In any case, if I turn off the 561 pF switch and invoke the other switch instead (hooked up to 2 parallel 561 pF or 1122 pF... you can see the pair of blue caps next to the other switch) then I can tune my next range from 1341 pF to 1808 pF. Then if I invoke BOTH switches, I'm basically now adding 1683 pF (3x561pF) so 1887 pF and reach a maximum of 2369 pF. So my ranges are as follows:
219-686 pF
780-1247 pF
1341-1808 pF
1887-2369 pF
Dead zones: 686-780, 1247-1341, 1808-1887. I can fix that by adding another trimmer or making my steps smaller and use another switch.
So I started working on this and I apologize in advance for the dog-food appearance of the wiring on the back and solder joints. As I get more practice and proper wiring I'm sure I will be able to route the connections better and have a nicer layout and better soldering job. My soldering iron is also one of those pencil-style mini dollar-store pieces of crap and I'm using telephone wire to make the connections.
Anyways, as long as it does the business that's good enough for now.
You can see above the "base" cap in beige, and then the switchable either single blue cap, or the 2 blue-caps (associated with the switches, respectively at the far right edge of the board). My 3 green large trimmers and smaller white trimmer. The easiest way to compensate for the "dead" zones is to add another green trimmer and then take 40 pF off my beige cap (I can use a 68 pF instead of the 151 pF). If I do that, my low end will be 68 (floor)+15(loop)+8(small trimmer)+4x15(green trimmers)=151 pF. My highest end would be 68(floor)+15(loop)+40(small trimmer)+4x160(green trimmers)+1683(both switches on)=2446 pF. So I would improve my range 151 pF - 2446 pF and eliminate the dead zones!
So once again I whipped out my LCR cheap-o eBay meter and tested it on my PCB and lo-and-behold I was able to tune in various ranges, from a low of about 216 pF to a high of about 2342 pF as you can see in the following photos:
So I went ahead and tried searching for some signals in the LW tuning range of my Tecsun, which was 153 -513 kHz. Unfortunately all that work for next to nothing!
There is not much activity in my area it seems, or at least I can't seem to find it. The loop antenna did help, I was able to find some signals but mostly just beeps and buzzes and strange noises. I found what I thought was MORSE CODE beeping at around 400-405 kHz and I tried to decode it:
- - . . / - / - - - / _______
Dash Dash Dot Dot (Space) Dash (Space) Dash Dash Dash (Space) ... a very very long Dash ...... repeats!
I figured out it was morse code for "ZTO" and probably some kind of radio beacon. I don't know what the long beep at the end is, but probably to indicate end of the message, start again. I did a Google search for ZTO and it turns out it was listed on
http://dxinfocentre.com/ndb.htm with the following information:
ZTO Frequency: 403 kHz
CAN, ON, Toronto - Woodhill
Power: 50
Coordinates: 43°44'18", -79°42'11"
So back on Google maps I went and look what I found!!!!!
That must be what I was listening to! I'm only about 20 minutes drive away, about 20 km or so but barely could make it out on my radio (lots of static and was playing with the tuning). So far I'm not too impressed with the LW aspect of the radio. Seems like nothing interesting is coming in and I while I had fun doing it and learning, it was a lot of work building that antenna and tuner just to pick out a radio beacon 20 km away (and I had to turn my antenna to point to it also).
Any ideas as to the state of LW signals in Toronto? Is that range fairly dead or am I just not having any luck with reception?