Joe,
First, yes, the low pass filter from a MrII are 50 ohms.
A new broadcast station normally has one year to resolve interference
issues it creates.
30 watts? Must be a translator? The out of band spurs need to be 60 db
or so down for this sort of equipment. A spectrum analyzer on your repeater
antenna would tell a lot about what you are dealing with. Is the
interference all across the six meter band or just in spots? Do you hear the
audio of the FM station? Is it clear or distorted?
How far is your antenna from the broadcast antenna?
This reminds me of an issue I had back in 1976. We had just purchased
our first frequency counter for the AM-FM stations where I was chief eng.
The FM was and is 50 kw ERP. The fancy new counter would read "94,500,000"
when connected to anything. I tried low pass filters, shields, transformers,
etc, to no avail. The final fix was a open quarter wave stub on a tee at the
input to the counter.
For your problem, Joe, I would try an open 1/4 wave stub at 94.7 at the
receivers antenna port. It will look like a dead short to 94.7. Just use a
piece of RG58. This will look like a parallel capacitor to your six meter
signal so you may need to retune your receiver input stage. Any filtering
you do will probably be more effective when used at the receiver or receiver
port of the duplexer rather than the antenna side of the duplexer and won't
screw up the SWR for your transmitter.
Take a look at the grounding scheme on your repeater and the FM
transmitter. It doesn't take much length of ground strap raise equipment
from ground at 50 or 95 mhz.
73,
Al, K9SI
> Date: Thu, 07 Jul 2005 01:12:53 -0000
> From: "Joe" <[EMAIL PROTECTED]>
> Subject: 6 meter repeater interference
>
> Hello to All,
>
> I just got a new neighbor at my 6 meter repeater site, a low power (30
> watt) FM broadcast station on 94.9MHZ. I now have low level
> interference on my MastrII repeater input frequency.
>
> As a simple troubleshooting tool, I thought about putting a low pass
> filter on the receiver or the antenna connection to the duplexer. This
> would attenuate any 94.9Mhz signal coming down the coax. My thoughts
> are to take the low pass filter out of a MastrII PA, but I don't know
> what the input impeadance to it is. Does anyone know if the final PA
> of a MasterII is 50 ohms into the low pass filter? I belive that it
> is, but not sure.
>
> 73, Joe, k1ike
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