Electronic – How to adjust receive-only antenna

antenna

I don't understand most of the antenna balancing instructions I read; for one thing they virtually all seem to assume the antenna is being used to transmit. In my case I am only interested in receiving. I do not want to transmit with the antenna. Basically my goal is to be as sensitive as possible and make the received signal as pure as possible.

For example, one setup I have uses a wideband antenna that looks like the following and can supposedly receive signals anywhere from 3 MHz to 800 MHz:

widedband antenna

The antenna is on a mast off the porch. I connect a coax cable to it and it goes about 20 feet to my receiver. Sometimes I connect it to an antenna switcher. It seems to work ok, but I have no idea how to optimize it to make it more sensitive.

I presume that some optimizations would be frequency-specific and others would help increase sensitivity at all frequencies, but I have no idea how to make these adjustments. I have an SWR meter, but the instructions for it assume that I am transmitting, which I am not.

To quote from one of the answers below:

When your antenna impedance matches the cable and receiver impedance
the signal power is optimally transfered… Some antennas have an
impedance matching adjustment on them. This should be adjusted to
match the cable and receiver impedance. Matching impedances for a
receiver only system can be difficult as there is not enough power to
drive an SWR meter. Sometimes the manufacturer will mark approximate
locations on the adjustment component that will indicate the impedance
settings. Without any guidance it would be necessary to tune your
receiver to a very week signal then make small adjustments to the
antenna, then recheck the signal for any improvement.

So, if it is good for the "antenna impedance" to match the "receiver impedance" how do I do that? How do I measure the impedance of either one? The poster just says it is "difficult".

One web site I read said antennas should be "DC grounded".

Best Answer

Antennas are reciprocal - they transmit and receive equally well (or poorly).

The reason it's important to tune a transmit antenna is because a mistuned antenna, by reflecting power, can destroy the transmitter output stage.

Tuning a receive antenna is much less important, compared to that!

Most receive antenna tuning is frequency sensitive, in fact in the crystal set days, the antenna was often part of the first tuned circuit, and re-tuned for each new station.

With a broadband antenna, there's really not much point making such adjustments.

However you can improve reception by:

if the received signal is weak, increase its height, or use a larger antenna better suited to that waveband.

if it's strong but contains interference, use a directional antenna to reduce the interference - or add a tuned circuit to reject the interfering frequency.

and so on.

These can make big differences in reception. If we knew what you are specifically interested in receiving, you may get more specific answers.