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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".

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  • \$\begingroup\$ What about the antenna is adjustable? What frequency range are you most interested in? If it's the one I know, a bit under 1 m tall, it's for maybe 100 to 1500 MHz. \$\endgroup\$ – tomnexus Feb 28 '15 at 6:52
  • \$\begingroup\$ As I understand signal engineering, I'm not sure that you can actually optimize a given antenna. Impedances need to match, cables need to be a correct multiple of wavelengths, connections clean and tight, and then after that its all signal conditioning and decoding, right? \$\endgroup\$ – Sean Boddy Feb 28 '15 at 7:00
  • \$\begingroup\$ One thing I know for sure would boost your reception is the use of a directional array antenna. That is, if it doesn't violate your design requirements. Which you could post. \$\endgroup\$ – Sean Boddy Feb 28 '15 at 7:09
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    \$\begingroup\$ Invest in or build a "noise bridge". \$\endgroup\$ – Optionparty Feb 28 '15 at 14:24
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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.

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This looks like a discone antenna to me and as such it has a lower frequency limit dictated by the sizes of the cone and the disc: -

enter image description here

The disc and cone don't need to be solid for this to work effectively. The higher frequency limit is dictated by by disc and cone spacing.

This means there is very little to do to improve performance of the antenna providing the design equations seem to fit what you have - see wiki link above.

Now let's consider what you mean by: -

Basically my goal is to be as sensitive as possible and make the received signal as pure as possible.

The type of antenna you have will be not very sensitive - it's wide band and omnidirectional - if you want a sensitive antenna then choose one with gain but what you'll find is that it won't be omnidirectional so you have to decide what you want - it's a trade off.

Another thing to consider is that because it is wideband it will be simultaneously receiving a vast number of radio stations and transmissions. It will also be receiving a wideband chunk of noise too. You might want to receive a particular frequency and you get sensitivity and selectivity from the receiver's ability to discard all the wideband stuff you don't want.

In short, it's the radio receiver that will give you what you want when using a wideband antenna.

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  • \$\begingroup\$ @TylerDurden did I answer your question? Do you have anything else to ask? Have you considered accepting one of the answers to this question? \$\endgroup\$ – Andy aka Feb 21 '17 at 18:29
  • \$\begingroup\$ It is a discone antenna. It is very wide bandwidth 10:1 . \$\endgroup\$ – Old_Fossil Sep 8 '18 at 4:45
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In your case the antenna is already rated as "wide band" so frequancy adjustment should not be a main issue.

Balancing for an antenna is often referring to the connection type and/or impedance matching.

Since you say you have a coaxial cable coming from the antenna this is considered an unbalanced connection. For best performance the receiver you use should also have an unbalanced connection (often a similar matching coaxial connector).

On some receivers (and some antennas) there is a two wire "balanced" connection, with both connections ungrounded. If you need to connect a balanced device to an unbalanced device you should use Balun transformer for best operation. See: http://en.wikipedia.org/wiki/Balun

On some antennas the output impedance might not match the impedance of the receiver (or of the cable). In these cases an impedance matching transformer or impedance matching Balun should be used. 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.

(Edit)
There are a few specialty Discone antennas with adjustable whip pieces at the top. For some of these antennas the adjustable whip section can help improve the lower end frequency range. Others include the extra whip piece to make the antenna useful for both transmitting and wide band receiving. When used for transmitting the adjustment of the whip section can be optimized for certain transmit frequencies, (in this case an SWR meter could be used). If you have this later type of antenna and do not plan on transmitting the whip section adjustment would not be very helpful.

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  • \$\begingroup\$ If I removed the BNC connector and attempted to make a balanced connection, would that improve the sensitivity of the antenna? \$\endgroup\$ – Tyler Durden Aug 30 '16 at 13:14
  • \$\begingroup\$ Sensitivity is not a function of a antenna. For that a good receiver is required. \$\endgroup\$ – Old_Fossil Sep 8 '18 at 4:42

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