Antenna Tuning

[PROXIMA-CENTAURI-B]

Hello my friends. The pic below shows my software defined radio. It can tune from 500 kHz to 1.7 GHz.
It comes with a telescopic dipole antenna that is also shown below. The telescopic dipole antenna is 6.5 feet from tip to tip while they have an angle of 180 degrees between them.

1) A person on YT, said that every antenna length needs to be tuned to the frequency it is receiving. This means, the actual length of the antenna needs to change based on the receiving frequency. (

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2) Assuming the person is correct, does it mean that I have to adjust my telescopic antenna length based on what frequency I am trying to receive?

3) My software defined radio can receive a 1000KHz station. That would mean, my antenna needs to be 299.80 meters long. ( Wavelength of 1000KHz is 299.80 meters ) But my antenna is only 6.5 feet long. Why am I still able to receive the 1000KHz station?

4) Assume, I am trying to receive a 327.85MHz signal. ( 327.85MHz has 0.9144 meters wavelength ) Am I supposed to reduce the length of my telescopic dipole antenna, such that it measures just 0.9144 meters, from tip to tip with 180 degrees between them?

My friends, to make a long story short.....if antenna tuning and the antenna length are very important, then why are we not required to adjust the antenna length everytime we change reception frequencies?

Thank you for the information my friends!

 

[prcguy]

The antenna you pictured is a dipole so for optimum reception it would be adjusted to be a half wavelength total from tip to tip. With 6.5ft being the maximum length that antenna will tune down to about 72MHz and if it will collapse to 1ft total that would be around 465MHz. And again for optimum reception you would adjust it to 1/2 wavelength long at every different frequency you want to receive.

Outside those ranges the antenna will just be a random piece of metal and reception will be degraded or just non existent. At some point that antenna will just not be worth using like below 50MHz and above 1GHz. Its more of a do all but not very good freebe antenna they throw in with some RTL type SDRs and its actually an old surplus back of the TV set antenna for the Asian market.

To get the most of your receiver and your sanity you will need to get a couple or several antennas to adequately cover the frequency range of your receiver and they really need to go outdoors and as high as you can get them. For a setup like yours the antenna(s) are probably 90% or more responsible for you receiving anything useful.

 

[ladn]

1) A person on YT, said that every antenna length needs to be tuned to the frequency it is receiving. This means, the actual length of the antenna needs to change based on the receiving frequency.

That's technically correct, especially for transmitting. In reality, for receiving, you have a lot of leeway with antenna length.

A properly tuned antenna will perform better (be more efficient) and give a more predictable coverage path.

3) My software defined radio can receive a 1000KHz station. That would mean, my antenna needs to be 299.80 meters long. ( Wavelength of 1000KHz is 299.80 meters ) But my antenna is only 6.5 feet long. Why am I still able to receive the 1000KHz station?

You are receiving the station because it has a relatively strong signal.

My friends, to make a long story short.....if antenna tuning and the antenna length are very important, then why are we not required to adjust the antenna length everytime we change reception frequencies?

You should try to keep your antenna length roughly compatible with the band your are trying to receive and the type of signals you are trying to monitor. If you are trying to monitor, say, weak HF signals, you will need the most efficient antenna and feedline system you can manage. If you are monitoring local VHF/UHF frequencies, then a relatively short antenna will be adequate.

Remember too, it's not just the length of the antenna, it's the overall design that determines frequency, polarization, and efficiency. Antenna location is also important. Generally, outside, high up, antennas work better than inside antennas.

 

[majoco]

If you really wanted to receive signals in the AM broadcast band, your best bet is a loop - either a fancy shmancy like the yellow wired one on a frame or an easy one wound on a ferrite rod - maybe scavenged from an old tranny radio or a rewound one. You need to add a coupling loop to connect to the radio via a plug like your rod antenna.

 

[spongella]

Great questions, excellent answers. You certainly purchased one of the best SDR dongles on the market.