Antenna diversity without diversity box?

[headhunter23]

I'm sure there's a reason as to why this isn't possible, but will ask anyways... is there anything that functions like the diversity video box, but is between the antenna and the rx? I would think it would be much simpler to have a single rx and more antennas to cover every angle, then the rx just selects the strongest signal from the array.

More simple than tracking system etc...

What do you guys think?

[Terry]

I looked into this idea many years ago when the price of a video RX was 100s of $. The main problem is you need the RSSI signal or the video from the RX so that you can choose the best aerial but to do this it must be connected. This means you have to switch aerials to sample what the other aerial can receive.

For a 2 aerial system it is possible to just switch the aerial as soon as the current one drops out, I have used this system on my UHF r/c RX and it works well.

The main drawback is than the RF switch will cause a loss of some signal to the RX, this gets worse as the frequency gets higher. The other problem is the switch speed has to be very fast to give true diversity.

A multi aerial system would need some way of sampling the aerials signal, this would need to be not only the strength but the exact frequency.

Terry

[headhunter23]

Soooo... too complicated and slow to do then? Like I said, don't know enuff about it... still seems the most simple way... too bad.

[Terry]

Well if you don't mind it dropping video for a second or so then you could make it so that when the signal is dropped it will switch each aerial in turn until a signal is found. Still going to loose some signal in the switches though.

Terry

[headhunter23]

What about it keeps using same signal until it checks the rest? Essentially, say antenna 1 is good, check, check, 2 seems better, switch. Having the system lag just as it needs to until a stronger signal is detected? If say signal drops completely from 1 it just switchs to a default, say antenna 5 is omni or that second strongest signal in mem.

Edited October 25, 2009 by headhunter23

[Mr.RC-Cam]

The reason the antenna switching method is not popular is because it is the most expensive and difficult to implement. Low noise / minimal loss microwave RF switches are several times more expensive than our common wireless video receivers. In addition, measuring the RF signal at the antenna will require a bandpass filter, low noise preamp, and RF power sensor assigned to EACH antenna. These things are essentially already in a typical video receiver.

In reality, you don't need the complete video receiver on each antenna. Your system could share a common baseband RF demodulator and employ a satellite tuner module (the sardine can) for each antenna. This simplifies things, but does not radically reduce cost.

If you have your heart set on the type of antenna you proposed then they do indeed exists. Antenna arrays are the basis of the designs used in electronically steered phased-array antenna systems.

[headhunter23]

Bugger, you'd think simple would be easier...

Thanks u 2.

Ivan.

[Terry]

Simple is easy, thats why I just use multiple receivers.

Terry

[elossam]

Simple is easy, thats why I just use multiple receivers.

Terry

Terry did you noticed in the image any kind of noise or image degradation due to the interaction between receivers? how far/close are any receiver from the adjacent?

[Terry]

No, I use 4 receivers one on top of the other, no problems. My 5.8Ghz version is on this page

Terry

[elossam]

Thanks Terry, will have a look to the link