Antenna amplifier for Beverage and large cardioid loop antennas

Chris Moulding

Recently on the forum there has been a discussion on building large (2m or 6 foot side) cardioid loops for 160m DX operation. This needs a loop amplifier with an input impedance around 450 ohms.

Today I've been asked if the Loop Antenna Amplifier + can be used with a Beverage antenna.

I've built a prototype amplifier based on the Loop Antenna Amplifier + PCB with a input transformer to match the 450 ohm load presented by a Beverage or a large cardioid loop antenna.

To test it I've built a quick lash to make a 2m (6' 6'') square cardioid loop antenna out of wire fastened around a wooden fence panel with a temporary ground using a screwdriver pushed into the soil. The bottom of the loop is only about 0.3m (1 ') above the ground. I fitted a 470 ohm resistor in the top of the loop to make it into a cardioid loop.

As expected this works well on VLF, medium wave and 160m but I was surprised by the performance on the 20m amateur band.

At the workshop for testing transmitters I have a wire up a tree which forms a 5/8 wave vertical on 20m. This is situated close to a large metal clad building which acts as a reflector towards Europe. As you will expect it's a good antenna with lots of big signals coming in!

I've attached an image with two screenshots taken using a RspDX SDR receiver 5 minutes apart to show the whole 20m band. This is taken on a Wednesday afternoon, no contests filling the band. The top one is the cardioid loop with the prototype amplifier, the bottom one is the 5/8 wave vertical. Here's a link in case the image doesn't show up on the daily digest:

There isn't much difference between the two, maybe some signals are stronger on the cardioid loop.

This week I'm building a batch of the new amplifier called the Beverage Antenna Amplifier. The price will be the same as the existing Loop Antenna Amplifier +.

I will be adding it to the web pages but if any one wants one immediately just order a Loop Antenna Amplifier + and let me know that you want the Beverage Antenna Amplifier.



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