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Off Air Audio
Topic: Antenna diversity system system for FM? Why not?

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Posted by Romy the Cat on 06-07-2009

I wonder why no one uses antenna diversity systems for High-end FM reception. The diversity systems are very popular in better car audio installations. All police cars use antenna diversity; many PA wireless microphones use antenna diversity, the wireless LAN networks use it.  Why not FM? In FM the diversity reception would practically eliminate any multipath that would be a huge benefit.

For instance not I have one rotatable external antenna:

It is rotatable, directional and I have excellent reception, in fact too much signal for my tuners with sub 1mV sensitivity. However, I live in city and multipath in city is always factor. It does not bother me too much as I have every low multipath numbers but I wonder if it is possible to get rid of multipath all together.

The basic of antenna diversity in my case would imply not one but two antenna: one at my roof and another antenna would be located  at the roof of next building. The signal from my antenna would not flow into my tuner but in an antenna diversity receiver/controller. The signal from the second antenna would also flow into the same receiver/controller. The antenna diversity receiver very fast (a few hundred thousand/millions times per second) switched the signal from antenna #1 to antenna #2, why doing it is measures the multipath numbers from each antenna and feeds the tuner with the signal from the antenna that has lover multipath number.

This is very common practice for many-many modern wireless receivers. What I would like to find a good quality diversity system controller that would be designed to work at 88-108MHz. I was looking and I did not see any. The closers that I was able to see were 50-75MHz, which is too low. I think it shall be the some diversity controllers made specifically for FM band.

The caT

Posted by Paul S on 06-07-2009
I think this has not typically been used for FM, but it is my understanding that some FM stations used to use something like this to monitor their own broadcasts.

Who knows how it has changed over the years, with digital, satellite and cable broadcasting, and the very sophistocated DSP/monitoring stations now use.

On the face of it, this is not just for urban areas, but it would also be great for hilly areas, like where I live now, for ghosting and the sort of inter-channel interference that plagues me now.

Maybe this would also fix the VERY WEIRD sort of "stuttering" I now notice sometimes, that I have taken to be the back and forth modulation of the digital/analog simul-casting of supposedly- "split", shared bandwidth.

Anyway, I agree that this idea has huge potential, but the last time I looked into the split antenna trick it was so expensive that it was out of the question.

Of course, what I really need is good programming...

Best regards,
Paul S

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