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Antenna used for receiving only - impedance importance?

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I'm currently looking at building some UHF (434mhz) yagi's, which will be used exclusively for receiving. I've come up with a few designs in software, though the impedance of them is not matched to my feed line (50Ω) - will I need to use a balun?

From what I understand, when an antenna is used for receiving only, the impedance match is less important than if it were being used for transmission. Could someone clarify if this is correct, and if a balun is still needed?

Thanks :)
 

Since it is a receive only antenna you will not have to be concerned with high voltages seen throughout the cable run caused by the poor VSWR. However, the impedance presented to your input Low Noise Amplifier will have an effect on it's noise figure. If your cable run has sufficient length and loss, it may solve this problem for you. Theoretically, 5dB of cable loss should improve the perceived load match by 10dB in return loss [S11].
 

Joel-Tang said:
If your cable run has sufficient length and loss, it may solve this problem for you. Theoretically, 5dB of cable loss should improve the perceived load match by 10dB in return loss [S11].
Click to expand...

But the NF of the system will increase 5dB, that will decrease the receiver sensitivity 5dB. I don't think this is a good idea.
 

No matter it is a receiving antenna or transmitting one. Impedance matching is very important. You have to match the antenna with your receiving equipment so that it receives and delivers the signal to receiving equipment efficiently for further processing.
 

For lowest noise, impedance matching of receiver antenna is mandatory. There are however many cases, where other objectives are more important, e.g. small size, high bandwidth, or precise field strength reproduction (for measurement antennas). You should also consider, that a receiver is not necessarily operating at it's noise limit, because enviromental interferences may be at a much higher level.
 

The puropose of a receive antenna is to take a small electric field per length and turn it intoa reasonable power level at the receiver's input. If you have a big impedance mismatch at the antenna, you are throwing away power before it even gets into the cable between the antenna and receiver. It means that weak stations may turn into un-receivable stations.

Another issue is if your receiver is not very well matched, the mismatch at the antenna can combine (at certain frequencies) with the mismatch at the receiver to further null the desired signal.

But, practically, make the vswr as good as you can an try it to see if it is acceptable.
 

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