antenna seperation

Useful information regarding antennas for SDR products.
gearjamer468
Posts: 4
Joined: Tue Sep 26, 2017 4:09 pm

antenna seperation

Postby gearjamer468 » Tue Sep 26, 2017 4:21 pm

as mentioned in the operating manuel, the sdr antenna must not be in the near field of any transmitting antennas ....

so, what does this mean ??? how many feet / meters should the sdr antenna be located away from my transmitting antennas..

i will be using a long wire for hf / a discone for vhf/uhf and a loop yagi for microwave stuff ..... on the sdr rcvr.

all intelligent answers welcome !!
Last edited by gearjamer468 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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F1BJB
Posts: 108
Joined: Wed Jul 15, 2015 4:24 pm
Location: Beauvais France

Re: antenna seperation

Postby F1BJB » Wed Oct 04, 2017 1:47 pm

This is a complex question there is no simple answer.
It depends :
On the transmitting power used
On the directional properties of both antennas
On the polarisation of the antennas
On the presence of filters in front of the receiver to reduce the signal of the transmitter
If you want to use both at the same time or just non destruction of the receiver

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LittleWalkerTalker
Posts: 2
Joined: Wed Oct 18, 2017 12:19 pm

Re: antenna seperation

Postby LittleWalkerTalker » Wed Oct 18, 2017 1:42 pm

Ok, how about these scenarios:

Ground floor SDRPlay connected by 75' of lmr 240 to a discone mounted atop a 10' pole that is mounted to a 3rd floor fire escape (Antenna will be ~30'-35' off the ground). Transmit will be an 8w HT on 2m and 70cm using a mag mount whip at ground level on the opposite side of the house.
Can the SDRplay and the HT be in the same room? How far from the HT transmit antenna does the SDRplay it's self have to be?

If I walk into the house while having a conversation on the HT and end up transmitting in the room with the SDRplay, am I going to wreck it?

What if the HT was on the discone and the SDRplay is connected to a random wire or some other antenna at ground level?



Last edited by LittleWalkerTalker on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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vk3alb
Posts: 19
Joined: Sat Jul 01, 2017 11:43 pm

Re: antenna seperation

Postby vk3alb » Wed Oct 18, 2017 9:04 pm

As F1BJB said, it's a complex question.

I think it's unlikely that your scenario would result in a issue for your SDRplay but it would be nice to have some peace of mind. One way to do that is conduct your own experiment using gear you may have in the shack.

We know the SDRplay should not be subjected to more than 0dBm at the input. At VHF/UHF S9 is -93dBm. If you were to put a VHF/UHF radio with an S meter in place of your SDRplay you could make a rough measurement of the signal level you get at the input. Key up the HT and watch the S meter. If it doesn't go full scale you should be ok. If it does go full scale you could try to determine the actual level by adding attenuation in front of your test receiver until you reach S9. From there you can calculate the input level.

Of course, this depends on your S meter accuracy, access to attenuators, shielding between the two antennas etc.

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Lou
VK3ALB

LittleWalkerTalker
Posts: 2
Joined: Wed Oct 18, 2017 12:19 pm

Re: antenna seperation

Postby LittleWalkerTalker » Thu Oct 19, 2017 1:04 am

Thank you :)

I changed the configuration this afternoon, added another 64' to the random wire. It now goes up to the railing of the fire escape, so about 6' below the base of the HT antenna, and then down to a pole across the yard. World of difference! Most of the original stretch of wire was stretching across the house with only about ten feet making it outside. With the random wire now being so close to the HT antenna, I'll just unplug the antenna connector on the SDRplay when I want to transmit on the HT.

I should have the proper connectors tomorrow to hook the SDRplay up to the Diamond X-30.
Last edited by LittleWalkerTalker on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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