I've had similar experiences at FM sites. The basic issue is that many
FM transmitters have a spurious spike about 1MHz wide right around
32MHz. Since 100Mbps and 1000Mbps ethernet use a base frequency of
32.5MHz, this is what causes your issue. If this spurious emission from
the transmitter has enough power, it will drop your links to 10Mbps.
>I moved our radios 35 feet away from the bottom their antennas and
still cannot link at 100BT.
I always try to be 30+ft away, so that should be a reasonable distance.
> I've tried ferrite rings on both ends, all cables are shielded and
grounded.
We also use fully shielded and grounded cables. By this I mean Shireen
with RF armor ends, and McCowan surge suppressors at the top, grounded
to the tower frame. We don't use any other special grounding mechanisms
(such as grounding the CAT5 shield using an LMR200 grounding kit - which
I've had suggested before, but never tried).
What we have found to be a successful tactic is using Ferrites -
however, it can't be just any ferrite, and it has to be installed in a
specific way.
We use a FAIR-RITE Type 44 snap-on (TYpe 43 or Type 44 are acceptable):
http://www.kregercomponents.com/fair-rite-products/0444164281
The solid equivalent is 2643540002 but you'll have to recrimp your
cables to use them. It does have higher impedance than the snap-on
units, though, so there is a slight benefit.
You must fully weatherproof these, or freeze/thaw will break them off in
one or two winters!
Next, you need to use enough of them. You must form a continuous line of
ferrites *for at least 12 inches*. One single ferrite _is not
sufficient_. We use TEN units on each end of the cable.
Next, you need to put them in the right place: The continuous line of
ferrites must start _no further than 10cm from the termination point_ of
the cable.
We have had repeatable success with this method at several FM sites.
It's not perfect, as sometimes a link will still kick down every now and
then, but it makes the problem a lot more tolerable. I suspect that more
chokes would reduce the frequency of "every now and then".
On 7/14/2016 3:18 PM, Marco Coelho wrote:
I have an existing tower that has a FM transmitter on it. I believe
they are just under 10,000 Watts.
Since we have been one that tower, I could never link up Ethernet that
runs up the tower to the equipment on the bottom at 100BT. I've tried
ferrite rings on both ends, all cables are shielded and grounded.
Always had to go to 10BT to get a link.
I moved our radios 35 feet away from the bottom their antennas and
still cannot link at 100BT.
The new radios require 1000BT too use them to full advantage. Ideas?
I'm considering conduit all the way up the tower. I don't want to put
switches at the top.
--
Marco C. Coelho
Argon Technologies Inc.
POB 875
Greenville, TX 75403-0875
903-455-5036
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