Antenna tuning

Thread Starter


Joined Jun 30, 2022
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. (

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!




Joined Aug 27, 2009
Receive antenna tuning/matching is important in the delivery of max power to the receiver input via a transmission line but max power is rarely the prime requirement in receiving a usable signal from a low noise signal source. Receivers are usually rated in a method that implies voltage sensitivity at the receiver input.

Sensitivity Microvolts 0.1 to 3 yv

A 'reasonable' length (for the wavelength of the desired signal) antenna for the frequency of reception will usually collect sufficient voltage without being tuned (resonant). Physical antenna resonance is not a requirement for EM transmission or reception but tuning/matching much more important during transmission of power at the frequency band of interest.


Joined Feb 24, 2006
Antenna tuning becomes important in transmitting at power levels exceeding 10 watts or so. The reason is that whenever there is an impedance discontinuity a portion of the transmitted signal will pass through the discontinuity and a portion will be reflected back to the source. Let us say that we have a 10 watt transmitter feeding a transmission line and an unmatched antenna. If half of that power is reflected back it is unlikely to damage the transmitter, but the part that passes through won't propagate as far.

Now let's raise the "price of poker" and talk about a legal limit (amateur radio) transmitter at 1500 watts that must deal with 750 watts of reflected power. This may actually do damage to the output stage if the condition persists for any appreciable length of time.

Such considerations just do not occur with receivers.

You might well ask what an impedance discontinuity is all about, but that is a topic for another thread.


Joined Aug 21, 2017
RE:""Why am I still able to receive the 1000KHz station?""
At very short antenna the radiation impedance becomes for a short antenna is very high, because there is a very high capacitative component to that impedance. Simultaneously, the resistive component, or more precisely the radiation resistance can very small (1 or 2 Ohms). Thus, when You want to circulate into antenna some Watts, te said is large problem. But when one wants to receive something, large impedance means extreme small current in the radio input - but who cares if input resistance may happen be Megaohms.