WA Radio Scanner Users' Group

Hello

I am planning on operating two dual band (VHF/UHF) radios in my shack at the same time (separate antennas). Say I want to have a QSO on 146.450 MHz and have the other radio tuned to the WIA news on 146.7 MHz or even scanning multiple service frequencies. My questions are:

• Would the receiving radio be overloaded when I transmit (5 – 10 watts) on the QSO frequency? If so, what would be the minimum spacing (frequency) required to avoid this?
• Is there also a minimum spacing (distance) requirement for the antennas? Can they be on the same mast?

You assistance would be appreciated.

73
Peter

Generally you should keep the distance between two verticals at least 1/4 wave length otherwise they can affact each other the same way directors and reflectors do on a yagi. Too close and the impedance of your antenna can change (which will send the SWR way off) If the antennae are on the same mast then you also need to keep distance between them and the mast.
I have two antennae about 1.5m apart on my car. One runs on 145.175 MHz APRS when mobile. It doesn't overload the voice radio but it does desense it so the audio drops out while the APRS is transmitting. It will depend a lot on the quality of your radios and antenna systems and the closeness of the frequencies in use.

The news is also on 70cm.. using different bands will help a lot.

You will get better isolation if you separate the antennas vertically rather than horizontally. Even then you may get some desensing as most amateur radios dont have a sharp enough front end.

Just to tag onto this, what about scanning/receive only? Does distance still play a part if you have two antenna's next to each other?

Thanks for the comments.

73
Peter