Fra-7700 Active Antenna Full Saturday Afternoon

Operation: The advantage of the pot over the fixed resistor is that you may adjust it for either maximum signal on BC or for minimum loading and noise on SW.

Thats the concept; filter first, then amplify or attenuate as needed.

Then look at the 2 DPDT push button switches which have been completely disconnected and rewired as shown.

Follow the insertion points A thru E and add the connectors of your choice.

Fra-7700 Active Antenna Full Saturday Afternoon

The first one took a full Saturday afternoon because I had to trace things out and design as I went along.

Later, you can make blow-ups and print those to study as well.

Changing, modifying, or altering any product, in any way, may invalidate any warranties, andor cause refusal of repair.

These data are presented here for informational and archival purposes only and do not guarantee any specific performance or operational standards.

The author cannot be responsible for others craftsmanship or workmanship.

Always disconnectunplug all equipment before opening the case or attempting to work on internal circuitry.

One is a low impedance input for a shortwave (HF) dipole, transformer (balununun) fed random wire, or similar antenna.

This is fine if you use the FRT-7700 tuner or FRA-7700 active antenna, but if you dont have, or use, those devices, or if you have completed the modifications on the above two devices, then the two ports are an inconvenience.

Analysis: Feeding the SW port only, causes a 36 dB loss when you tune the BC band.

Feeding just the BC input gives you virtually no signal for the SW bands.

I tried several design approaches in an attempt to unite these two inputs.

On the test bench, several measurements were made in each condition, on each band, with every permutation possible.

The higher value of separation offered by the pot allows the front end to give max.

The 100:1 ratio (difference between the pot and fixed resistor) only buys you a few dB, and a 2K to 5K pot will suffice, with a 1 to 2 dB loss.

Using the fixed resistor will spoil the sensitivity by anywhere from 2 to 4 dB.

If thats a big deal to you, then use the pot method, not the fixed resistor.

Since I already have electro-OCD, I decided to drill the chassis and go for the full flexibility by using a mixing pot.

Use a carbon composition or carbon film type, not a wirewound resistor).

Note that the SO-239 connector is already connected to the SW circuitry.