12 Foot Circumference Mobius Loop Antenna...

[Robot Matrix]

Built this yesterday (2/1/25 central time) and had it on the back deck for testing. SO quiet! Today, I went to Lowe's and bought two 20 foot plus lengths of tapered, black poles from the fencing section, and put the antenna up on that. I painted the wood that I made attached the loop to, black.  The balun is made from 43 mix, though I plan on using another type in the future.

Radio blackout and all today,  I could still pick up CBer's running high power, hams running power, a few SW stations including WWV, plus WWVB, and longwave Navy stations on my WEB-888 SDR. There were even, still, hams running contests from Canada on 10m through thick and thin. NOT a great day for contesting.

Anyway, picked up decent signals from 40 and 80m after the sun went down. Not great,  but since the noise floor is so low on this loop, very readable.

Outside of the noise caused by the switching power supply on certain frequencies, the noise floor is around S1. I plan on building a linear power supply for this SDR to get rid of all that. 

Anyway, here's the pics:

[ChrisSmolinski]

Congrats!

I switched my LZ1AQ style Crossed Parallel Loop to passive, removing the pre-amp and replacing it with a transformer to coax feed back to the shack. It connects to an AirSpy HF+ Discovery, which has sufficient sensitivity to pick up even weaker signals. And as you noted with your loop, with a very low noise floor.

[Robot Matrix]

Congrats!

I switched my LZ1AQ style Crossed Parallel Loop to passive, removing the pre-amp and replacing it with a transformer to coax feed back to the shack. It connects to an AirSpy HF+ Discovery, which has sufficient sensitivity to pick up even weaker signals. And as you noted with your loop, with a very low noise floor.

Thanks. I DID make one big mistake that I caught last night while reviewing pictures I took, and had to rectify today.... I failed to ground both sides of the braid part of the coax of the loop antenna (as seen in the 2nd pic)... so I brought it down today and fixed that. Had to solder the new connections while on the roof. I didn't take a pic of the correction as the wind started picking up due to the incoming cold front and I just wanted to get it done. I'm glad my wife and youngest son were helping to hold the antenna mast and ladder. Went from 72 to 52 degrees in about 30 minutes flat! Even blew over a chair on our deck.

So, that being all done, I was still getting a little noise that I didn't think I should be getting, especially while the loop is pointed N-S. So I checked all grounds, power supplies (which I did find a linear 120 to 12V power supply, but can't verify that the 12 to 5V isn't a switching supply), and finally the FM trap. Once I took out the Nooelec FM trap, almost all the noise disappeared! Which, is contrary to why I hooked it up in line with my SDR! Why would it do that? Its a passive device. Once removed, all the noise disappeared, but then two nearby FM radio station artifacts reappeared just below the CB band and up around 30 MHz. Mabye I just need a LPF for 30 MHz and below instead? Its a little puzzling.

Anyway, I got WWVB 60 kHz, and after dark the Navy signals around 20kHz, NDB's, 160m traffic including local nets near KC, 80m, 40m all back... though I wasn't expecting much below 1 MHz. Signals on MF are just booming tonight.

Its nice seeing a noise figure around S1 instead of S3-4. Sometimes I can pick up signals that I can hear that I can't even see on the waterfall. Blows me away.

I still plan on building a linear regulated 5V power supply. Problem is, the regulators are rated for 1.5 amps and I need at least 2-3 amps. I'll have to do a little research. I'm just trying to give this SDR a very PURE 5VDC.

[ChrisSmolinski]

I still plan on building a linear regulated 5V power supply. Problem is, the regulators are rated for 1.5 amps and I need at least 2-3 amps. I'll have to do a little research. I'm just trying to give this SDR a very PURE 5VDC.

One option might be to just buy a used linear power supply. You can find them on eBay for around $30, often with 5 or 6 amps output at 5 volts. Check for Power One and other well known brands.

[Robot Matrix]

I might do that. I know it's not all my PS as this is a noisy neighborhood. I'm pretty happy with it the antenna so far. I might see how well it does on VHF air band at some point.

Take a look and listen I'd you'd like
http://75.134.33.242:8073/

The loop is oriented east/west.

[Robot Matrix]

So, turns out the bulk of the noise problem was a faulty PL-259, which intermittently caused the coax to become an antenna with LOTS of noise. It was a crimp type that came with the coax. The other end of the coax, at the antenna, was already replaced by me a while back. But the one on the radio end was the crimp type. So, I cut it off, pitched it, and put a soldered a new one on. After re-introducing the FM-trap, there was no new noise and the FM artifacts, once again, disappeared. I forget I've had all this coax for 20 years. I'm examining all my loose laying coaxes now since they're all aged and who knows what condition they're in. Heck, I might buy new coax as long as its all copper. Still, the loop is quiet, but I can't tell if its TOO quiet given the conditions lately. I AM getting static crashes tonight from storms in KY/OH area. I know every antenna has its compromises, especially when it comes to broadband vs gain. Still need to test it on the lower VHF band and see how it performs.

[Robot Matrix]

So, using 50' of RG-58, with the antenna made of RG-6, and after repairing the connections, I've concluded I need a preamp with this loop antenna. Only strong signals were coming through and I was missing much of the spectrum, like I lost half of what I had. While it is electrically quiet, it's also RF quiet,  which is what I didn't want.

The first mobius loop I ever made was out of RG-8 and only 6 to 10 feet away from the sdr. It was fantastic with no preamp at all! I guess I didn't take long line losses into consideration with this latest iteration.

So, I've moved on to another project where I made a 9:1 balun and a random wire length antenna.  I'll post about that. 

It's all good... I LOVE building my own antennas.