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.
KiwiSDR (http://kiwisdr-m0kwr.ddns.net:8073) I am very impressed with the performance of the KiwiSDR.Although I was still suffering from overload from a nearby AM transmitter. I have installed a high pass filter in the antenna line just before the switch box and reduced the overloading to an acceptable level.
Some really interesting loop information on this site. The Welbrook Loop exposed.
George Smart - M1GEO
My antennas are always changing when 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.
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.
This is a unique 1:1 transmission line transformer intended to provide highest possible isolation between input and output. Consequently there is no direct electrical connection between the input and output with all RF energy being conducted through the specialized iron powder core. Specifications meet the K2AV FCP Isolation Transformer requirements for use with his Folded Counterpoise for 160 or 80 meters.
All photo's © 2003-2018 Kent Royce. Copyright Kent Royce 2018
I used an FCP inverted L for a number of years with OK results but nothing to convince me it was better than my original inverted L with just a few radials. I decided to try the inverted L in this configuration for a while without the shunt coil. In this configuration it worked OK but with 25 Ohms at the point of resonance but it was not a good match on 1946 kHz. I decided to have a play with the coils at the base of my inverted L. I connected the Antenna Analyser and found the usual 25 Ohms at the feed point on the FCP. I then connected my old loading coil from the FCP antenna side down to the top of my original shunt coil. To my surprise I had a match of 45 Ohms and X = 0 @ 1946khz so I was just where I wanted to operate. I have to admit I wasn’t convinced I had improved anything regarding the performance of the inverted L but to my surprise it was much better and I can only put this down to decreased losses. I am still testing and comparing the inverted L to my doublet but the inverted L is proving to be much better than any previous inverted L antennas I have made. Testing continues.
You must visit this web site for loads more information about FCP Antennas
FERRITES?? DO NOT use ferrites. This is a transformer, NOT a balun. There
is a voltage differential across the winding. The winding will go lossy.
We wind up overheating ferrites and cracking. This is not a balun with
guaranteed 100% cancelling counter-currents. Powdered iron is required.