Due to ever increasing noise on our HF bands I have been looking for alternative ways of reducing the pain of all this disturbing interference.
Scott (G8EQY) made a couple of these Wellgood (M1GEO) loop amplifiers to see if they were as good as my original Wellbrook Loop. I found Scotts loop much better with a lower noise floor.
I have been using Scott’s version of the wide aperture Welbrook loop for the past year and it’s been working great. I can't say the same for the Wellbrook Loop though. The Wellbrook Loop died after 9 months months. I put Scott's loop up in the usual dimond configuration on a cheap rotator at about 6 feet off the ground. I used a radom peice of wire 8 meters long. This worked great but i needed to keep rotating the loop to pick up weak signals.
After a few months I started doing a bit of internet research on loops and different shapes and I decided to try a double loop.
I connected 12 meters of cheap multi strand wire in a double loop configuration. I connected this to the amplifier at the bottom. See picture below. This configuration still allows you to null out a local noise source but gives you a improved sky wave reception.
When you have a receive loop or mini whip or any other receive only antenna for that matter you want to make sure you don't transmit RF into your receiving antenna and then into your radio causing expensive damage to your radio. This is a serious thing to consider when you install any receive antennas.
This perfect solution was designed years ago by Gary, KD9SV.
To avoid this problem some form of switching is required to stop RF getting into your radio or receiver. Some radios are equiped with a dedicated receiver antenna socket but I prefer to go one step further.
A good protection circuit to eliminate the possibility of blowing your receiver's front-end while using these auxiliary receive antennas specially on low bands.
I connected my loop to my newly acquired KiwiSDR (http://kiwisdr-m0kwr.ddns.net:8073) and I was very impressed with the performance of the receiver. I still suffered from overload from a nearby AM transmitter so I have installed a high pass filter in the antenna line just before the switch box,
Some really interesting loop information on this site. The Welbrook Loop exposed.
George Smart - M1GEO
My antennas are always changing but at the time I wrote this I only had 2 antennas.
A 220 ft inverted V doublet @ 40ft for all bands and a 160 meter inverted L as my main 160 meter antenna.
My 220 foot doublet makes receiving on the 160 meter band almost unworkable for weak signals but this loop has made all the difference right through the HF bands. The loop provides good coverage from 10 Khz to 30 Mhz. I owned a Welbrook Loop but it only lasted about 9 months before it failed.
My experiments with making receive loops and trying to reduce that dreaded QRM.
Front End Saver
Top Band Receiving Loop.
Amateur Radio for fun
OK so what does it do? In simple terms it disables your receiver antenna before switching your transmitter to TX. Connect your foot switch or TX button to the box/panel then connect your transmitter PTT line to the box. The coax through the box is cutting off your receive antenna before your transmitter goes into transmit. I use this to protect my Kiwi-SDR and my IC7700. My FT2000D, TS2000 and Icom IC7700 have a receive antenna sockets but i still use this added protection. All my transmitters are connected through the box and one PTT button is in use.
I was discussing this RF problem with a local Radio amateur G8EQY who has facilities to hand to produce the circuit board for this project. The following week Scott gave me the finished and built circuit board ready for testing. Totally unexpected and an amazing quality job. See the pictures of Scott’s completed project. The relays used are HJR1-2C L-12V DC which have an operate/release time: 6/4ms and these work very well.
High Pass Filter