Horrible Interference on repeater

[jcefd10]

What was the ERP limit on the other user's license? I've seen licenses where it was less than TPO due to issues like this where the coordinator did the path loss calcs but the install crew left the transmitter at full power.

Did you run any of the coverage prediction programs on the web?
I have some sites listed here.

why are you reading way up here?

If anyone has some to add let me know.

Their maximum ERP is 300w.
The radio shop that maintains that system said he couldn’t believe it reached us. He said it’s just an antenna on the water tower about 100’ in the air.

I didn’t use any software, just researched everything I could on RR and the FCC site to see who within a 150 mile radius was licensed to TX on that frequency.

 

[12dbsinad]

Their maximum ERP is 300w.
The radio shop that maintains that system said he couldn’t believe it reached us. He said it’s just an antenna on the water tower about 100’ in the air.

I didn’t use any software, just researched everything I could on RR and the FCC site to see who within a 150 mile radius was licensed to TX on that frequency.

300W ERP on VHF is a lot of power. They're probably running a full 100W out of the PA, how much gain is their antenna? VHF can travel a LONG ways point-to-point.

 

[speedway_navigator]

I wonder how the metal ground plane of the water tower affects propagation, I imagine the tank is 1 or 2 VHF wavelengths in radius.
Doing the free space path loss calculation I get 124 dB loss for 155 MHz at 150 miles.
If the repeater is 100 Watts I'd estimate under 60 at the antenna for coax and other losses.

50 W is 47 dBm, 47-124 dB loss leaves a signal level of -77 dBm, about 43 dB above a -120 dBm receiver cutoff level.

 

[lenk911]

I wonder how the metal ground plane of the water tower affects propagation

In the early 1970's, when the open dipole series (DB-224-264) was developed by DB Products, there were reports of adverse downward reflections from the antenna to the tank then upward to cancel the the lower portion of main radiation lobe of the antenna. The end result was a donut pattern. Extended coverage at the horizon and above and a large cone of silence around the antenna. GE Mobile engineering cautioned against using a phased open dipole style antenna on large mushroom tanks . The colinear style (20-foot fiberglass)was recommended instead to minimize downward radiation. Check the horizontal radiation patterns of each to see why.

 

[speedway_navigator]

My first 2 way job was with a GE dealer. San Diego PD had their portables and I had a similar model. I would stop in at the Dairy Queen and get a chocolate shake about twice a week and got to know the girls behind the counter.
One day I happened to look at the price for the shake and noticed I was paying under list price, so I asked why.

"police discount" was their answer, they assumed I was a cop because I had the portable on my belt.
Another time a female cop stopped the owner and I in front of the shop and asked it we were officers, she had spotted our portables, had no clue non public safety had them too.

 

[WB5UOM]

Humm Speedway...tell us more about getting to know the girls....just kidding.

 

[jcefd10]

300W ERP on VHF is a lot of power. They're probably running a full 100W out of the PA, how much gain is their antenna? VHF can travel a LONG ways point-to-point.

That, I'm not sure about. He didn't go into an extreme amount of specifics.
I do konw that when we called the FD to try and get in touch with someone, the conversation went similar to this :
"This is The FD from Webster CO Ga calling because we're having radio trouble and think it's your channel that's causing the trouble". "Hold on, we're having radio trouble too, bad. Here's the CHief".

So I don't know what kind of trouble they're having, but they were saying briefly that they couldn't even talk on their own stuff half the time. They were about to take the transmitter from the water tower and build a new tower site somehwere to see if it helped.

Guess I just got lucky.