Time to revisit the coax loop.

[KJ3N]

I made this thing a couple of years ago and didn't seem to have a lot of luck with it. I think it might have been because it was too close to the house, which has aluminum siding. It might have also been the fact that it was only about 2 feet off the ground. In any case, I put it behind the shed in the back yard and left it there.

Well, after spending the better part of 2 months adding to the radial field of the 160m antenna, I decided to resurrect the old coax loop. This time, I tried to find a better place for it. That place wound up being mounted to the back of the same shed I had left it behind to rot.

Now, I only got it mounted yesterday (Thursday), and only played with it for about 2 hours late last night. So far, I've got to say I'm having better luck this time around. Yes, without an external preamp the signals are down quite a bit, but the S/N ratio appears to be much better with several of the signals I found. In a couple of cases, SSB signals that were barely higher than my s7 noise level (and were a major problem to discern at all) suddenly became perfectly copyable against an s3 noise level. Of course, having it on a cheap rotator to null or peak signals doesn't hurt, either.

[PA5COR]

Reason i made my own amplified loop 1.5 meter cross and long tailed pair BFW 16 A ( 1.1 Ghz) class A amp.
Set against the shed away from the house the inverted L is used to transmit, the FT 2000 D receiver port is connected to the loop.
Broadbanded it works from 50 KHz to 50 MHz.
The OCF ( 160 - 10) horizontally is just one setting away on the coax switch, so receptionwise i can pick 3 antennae for it and see which one works best.

[w8nsi]

Reason i made my own amplified loop 1.5 meter cross and long tailed pair BFW 16 A ( 1.1 Ghz) class A amp.
Set against the shed away from the house the inverted L is used to transmit, the FT 2000 D receiver port is connected to the loop.
Broadbanded it works from 50 KHz to 50 MHz.
The OCF ( 160 - 10) horizontally is just one setting away on the coax switch, so receptionwise i can pick 3 antennae for it and see which one works best.

I am finding a need for a good low noise loop. Do you have anywhere a diagram for your loops system? I need it mainly for receiving in the 4-6 mhz range but because your is amplified and wide band I could use it all over.

[PA5COR]

Just a long tailed pair, i'll have a go at the schematic.
http://www.qsl.net/m0ayf/active-loop...g-antenna.html

I adapted that schematic for the BFW 16 A transistors, putting them in full class A mode.
I can run 1000 watts 20 feet away in the inverted L and the amplifier has no bad hiccups from it.
from the article:
In order to improve the antennas high frequency performance it may be worth trying different devices with a higher frequency cut-off and/or a lower noise figure. Using a pair of matched devices may also give improved performance by virtue of the reduced distortion. Using devices capable of higher collector dissipation it should be possible to increase the standing current and further improve large signal handling capability. In an e-mail exchange John (G8CQX) pointed out that “If you keep the collector resistors high and double the supply voltage you might find it works better as the increased open loop voltage gain will increase the feedback and reduce the input impedance further improving the linearity of the amplifier”.
That is exactly what i did, the BFW 16 A transient freuency is 1.1 GHz, 1 watt dissipation and low noise.
Get a similar transistor pair.

The loop has been successfully used to receive signals from L.F. (60 kHz MSF time signals) to 30 MHz. The receiving loop has also proved successful for receiving very weak signals associated with QRSS operation within the 20, 30, 40, 80 and 160 Metre bands. If you are also troubled by local QRM sources on the lower HF bands then give this antenna a try, you may be pleasantly surprised at the results.

Using the better transistors expect a decent amplification and usable frequency range from 20 KHz up to 50 MHz depending on the choice of in/output capaciter values.

Put it up as far from the house and other noise sources as you can get it, there is some directivety in the loop, so experiment how it is pointing to your most favourable direction.
If any receiver overload is observed check if the transistors are really in class A configuration, i.e. 1/4 of the max current is now bias.
Then use an attenuator at the receiver that will kill the overload, do not reduce the amplification at the amplifier.
In my case the transistors get quite hot, so use heatsinks to cool them down.

I did not use the relay that switches the loop antenna from the amp during transmit.

Hope this helps...

Lots more info here: http://g8jnj.webs.com/activeantennas.htm