RX loop antennas

[Mike43]

Hello,
I am a long time SWL and a bit long in the tooth for scrambling over roofs and up ladders. So I have invested in an MFJ 1886 RX loop antenna and need some help to get started with it. The antenna is mounted on a High Gain AR 500 rotator about 6 feet above my roof line. Where do I start. For instance I have always tested any antennas by receiving Shannon volmet, it was always there. With the loop would I get my compass out and just point the receiving edge of the loop in the general direction on Shannon and then just rotate the loop until I receive the signal. Also do both edges of the loop receive signals the same whichever edge of the circle you use. Thanks for any help, greatly appreciated.

[sinus trouble]

Hello Mike43!

I am no antenna expert? But magnetic waves propagate 90 degrees away from the turns of the loop if that makes sense?

For example? If point an imaginary arrow through the centre of your loop? That is the direction of where the signal strength will be strongest!

I hope that helps?

[Mike43]

Thanks for reply, I am getting there slowly and gleaning information as I go. Thanks again.

[Zozo]

Hi Mike, not to sure of the topology used in this particular loop you're using, however it should perform similar to most conventional loop antennas, whether that be for RX / TX or both. Going by my experience from building numerous loop antennas, mostly for 40mtrs the "business ends” or "each side" of the loop in your case will yield the maximum receive. The "Null" is going to be though the loop, however any strong local transmission will throw that convention out the window, and you will likely receive that signal regardless of how the loop in rotated.

Like I said the topology is unknown, Maybe a variant of a mobius loop, however its wide band receive, so it’s not going to have a Hi-Q like a tuned coupling loop. Hence the reason for the pre-amplifier that’s bias Tee’d into the coax.

As you have a rotator, I would align one side to 0° degrees, so that 90° on your rotator control box will be through the loop. But you won’t be able to use just one loop as an ADF fixed to a rotator.

Below Fig. Taken from MFJ Manual.

MFJ 1886 RX.png

[Zozo]

As we're talking loops, here's a small hand held Octagon loop I built for 3mtrs. It has a very Hi-Q when turned to the operating frequency. I've even TX'd using this little antenna using a QRP linear amplifier I built from a 2SC1971. VSWR was 1.1:1

Perfect for DF use too.

Octagon 3m.jpg

[Mike43]

Thanks for the info', I love the little antenna built for 3 meters. I love soldering and have built many antenna tuners and tried many types of antenna. I live in a bungalow with an odd shaped garden so no chance of doing the stuff I want. Even with bits of wire in the air I have had some good results. I have a QSL card from the Marianas islands so chuffed with that. Once I get the hang of this loop antenna I will be building more, I have loads of wire and cable laying around. I also have a scanner with a discone antenna about 10 feet above my roofline and listen to the shipping band a lot. The SAR helicopter is stationed at Lydd airport about a mile from my home, I have the SAR helicopter frequencies in the scanner and can listen to the crew onboard as far as Eastbourne in the west and almost to the Thames estuary in the east from where I live near Dungeness in Kent. Starting to waffle now., Thanks again for information, very helpful.

[Zozo]

As you have lots of wire to play with, I'd be recommending either an "Inverted L" or "Marconi T" as good general coverage antennas for RX. These will work well from VLF to the top of the HF bands, plus your have mixed polarisation.

Obviously these types of antennas will have a very high impedance, so your receiver will need to have a Hi-Z antenna socket. But I doubt that's going to be a problem for you seeing as you build your own home brewed ATU's. However being in a bungalow with odd shape garden might make it a problem to install such antennas. It's handy to have a few high trees to support them.

Although I do prefer to use vintage communication receivers, typically valve based. I do tend to use my SDR's more. They're defiantly worth a try if you haven't already got one? But if you haven't and thinking about getting one, avoid the cheap 8Bit RTL dongles. Go for 14Bit SDRPlay hardware as a minimum.

Also well done with QSL from Marianas islands, over 7000 miles away. Nowadays it's mostly eQSL cards I get which doesn't have the same impact as a physical card via post.

[Medley2k]

Agree zozo the eQSL cards are not the same as physical cards via post.

[Albert H]

Well done on the Marianas Islands! My most obscure QSL was from Jan Mayen Island (up in the Arctic Ocean and usually uninhabited!). I was repairing an early KW SSB rig, and answered a weak CQ with a weird /A callsign. The KW was only good for about 10 Watts on 3.5 MHz, and the contact was with some expedition to the island that went to examine its volcano. My aerial (such as it was) was just a random length "sloper" tied off to a tree at the bottom of my garden!