- August 10, 2010 at 3:12 am #7511radio8zSenior Moderator
Total posts : 247
In another post I mentioned that my vehicle has two antennas, one embedded in each rear side window and I speculated whether this was a true diversity system as opposed to just using a network to combine the signals.
A true diversity system would use two receivers and two antennae and “vote” on the best signal by some criteria (noise for example) and switch the audio output accordingly. It appears the technology for this is available for use with a single receiver.
While searching for something else I came upon this datasheet:
This IC connects to two antennae and by monitoring the noise in the received signal switches to the best one. The advantage to this for mobile reception is obvious but I can conceive of stationary situations where it could be nice to have. Just posting this for general interest and the good of the order.
NeilAugust 10, 2010 at 10:32 pm #19337MICRO1700Guest
Total posts : 45366
Hi Neil: At the university where I work they use
lots of FM wireless mikes. The receivers all use
diversity reception. (As I’m sure you know.) The data
sheet you mention is very interesting.
My Part 15 FM station has been lent out to some kind
of music event that is taking place later in August. So
my C Crane transmitter, a mixer, and an audio processor
are not here right now.
I dug up another board and processor from the junk pile.
The transmitter in use right now is a North Country Radio
MPX-96 that has been modified for Part 15.239. This transmitter
kit can do stereo or mono.
I have been listening to the my FM transmission as we pull out
of the driveway in our car. Running stereo, at the end of our
driveway, (about 50 feet from the house) there is a deep quick
null. As we pull out into traffic and proceed down the street,
there are other deep nulls, but an otherwise OK signal until
a few hundred feet from the house, when things start to degrade.
About 700 or 800 feet from the house the signal is gone. The
last few hundred feet the signal is copyable but noisy.
I went into the house the other day, went to the transmitter,
and flicked the stereo/mono switch to mono.
Out in the car, on the same path from the house to the loss of
signal, everything is the same in mono, except that those
deep nulls no longer exist. So things are smoother until
fade out, and fade out still happens in the same place.
I know we’ve covered all of this many times before, but I
thought this data was worth submitting. Maybe if our car
radio had diversity reception, those deep nulls would never
Bruce, MICRO1690/1700August 17, 2010 at 7:02 pm #19350radio8zGuest
Total posts : 45366
Bruce, I always appreciate hearing other’s experiences. It appears that my new vehicle with the diversity system performs somewhat differently than the old one did with a vertical antenna. I noticed the FM fadeout is at about the same range but within range it seems quieter without noticeable nulls. I don’t listen to FM while mobile so I don’t have any useful comment about comparative reception of licensed stations.
The AM performance is about the same noisewise but the range is greater. Just speculating but I run a horizontal AM transmit antenna and the receive antennas in the windows run mostly horizontal. This also could be due to a difference in the receiver sensitivity. I don’t know if the diversity system works for AM.
So, based on all the things I don’t know I can’t provide a good comparison, just an anecdotal observation.
NeilAugust 18, 2010 at 10:20 pm #19359MICRO1700Guest
Total posts : 45366
Well, it sounds like you have a really good car radio.
The FM diversity circuitry must work well.
If you have diversity on the AM band is a good question.
I suppose anything is possible.
As a casual AM/FM/TV DXer, I can say this:
Last summer in the car, during an E-skip
opening, I had great reception of a Thunder Bay,
Ontario (Sp??) Canada station for about 20 minutes.
It was during a local thunderstorm here in Connecticut.
If the car radio had diversity reception, the downward
fades might not have been so pronounced.
When my local neighborhood friend and I jumped into
the radio hobby in 1968, after a short time we had
a spectacular reception of a Pensacola, Florida FM station
one summer morning, again, here in Connecticut.
My buddy started up a reel to reel tape machine, and we
listened to the absolutely perfect signal for about an hour
and a half. Even once in a while there would be a very
quick, dramatic downward spike in the signal, and then it
would recover. I can’t describe the downward spikes. It
would be something that you would have to hear. They were
very deep and very brief, perhaps a few tenths of a second.
All the rest of the time the signal strength meter was either
pinning, or near the top.
After the station faded out, we just sat there. We didn’t
know about sporadic E. We had no idea how we could
have heard Florida way up here. As the years went by,
we both logged many E-skip targets on FM and TV.
But that first one was very exciting.
So, if you ever find yourself in the middle of an E-skip
opening (or tropo) when you are out in the car, it looks
like you’ll have the right radio for the job.
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