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.

 

[speedway_navigator]

These documents were mentioned during today's APCO webinar on licensing, I had never heard of Carey R6602 curves.

https://docs.fcc.gov/public/attachments/DOC-310600A1.pdf

This is old enough it mentions c/s, not MHz.

I found this while searching for the Carey info.

Urgent Communications

Urgent Communications

urgentcomm.com

It has a technical error in paragraph 5 for those with eagle eyes like me.

 

[12dbsinad]

These documents were mentioned during today's APCO webinar on licensing, I had never heard of Carey R6602 curves.

https://docs.fcc.gov/public/attachments/DOC-310600A1.pdf

This is old enough it mentions c/s, not MHz.

I found this while searching for the Carey info.

Urgent Communications

Urgent Communications

urgentcomm.com

It has a technical error in paragraph 5 for those with eagle eyes like me.

Ha! You know what that article is full of?? A bunch of BS. When someone output is your input (properly licensed VHF) you can take those "advances in technology" and stick it were the sun don't shine..

 

[lenk911]

Carey R6602 curves.

The Carey curves were developed in the late 1940's. They were developed before we had computers and their software that would approximate the real world of radio coverage. They are NOT an accurate indication of the performance of a radio system. They really are a definition of a system's boundary--like a property description.

A system's boundary consists of two contours. The inner contour is called the service (C) contour and the outer, the interference (I) contour. FCC rules are written around the concept that to have a clear channel your service contour cannot be crossed by the co-channel's interference contour. If it does, the applicant cannot license in most FCC radio services (i.e. broadcast and common carrier). In Part 90, the applicant may license if they agree to accept the interference and get written concurrence from the interfering station. When you see the term "Safe Harbor" in the Part 90 rules, it traces back to Carey. In Part 90 there is about 18 db difference between the C and I contours. This assumes the signal to noise is sufficient to have a receiver capture the desired signal.

Clear channel does not mean you never hear another on your channel. In FCC terms it means your receiver on a clear channel should capture the desired the channels signals at all times unless you don't have clear channel rights.

 

[speedway_navigator]

Do the curves take terrain into consideration? Have these changed since the switch from NTSC analog to digital? I heard stations had to reduce power to avoid co channel RFI.

 

[lenk911]

Do the curves take terrain into consideration?

There are two factors to determine when using the Carey curves. The first is system effective radiated power, ERP. If the antenna is directional, then the ERP should be calculated to the 8 cardinal points (N-NE-E-SE etc) of the compass. In Carey, ERP is in relation to a kilowatt not a watts like used in two way systems.

The other factor is the HAAT. The Height Above Average Terrain of the antenna is calculated from 2-10 miles from the site for each of the 8 cardinal points of the compass.

Carey is used in Part 90 but beware of the following factors. Like stated above the ERP is in relation to a kilowatt and the receive antenna is assumed to be 20 feet not 4-5 feet as in two way. While Carey is the official, I have seen the frequency coordinators consider the Longley Rice computer model as calculator of the C & I contours.

 

[speedway_navigator]

I've seen an ERP less than TPO which I figured was based on a contour setting.
Do you have a blog or podcast?
You don't post very often but it's obvious you have a deep technical and engineering background.

 

[AM909]

I've seen an ERP less than TPO which I figured was based on a contour setting.

This one was kind of funny: WQZU353 has 100 W out, 64.6 W ERP.

 

[lenk911]

: WQZU353 has 100 W out, 64.6 W ERP.

While it doesn't make sense to buy a 100 watt transmitter, have a 10 db gain antenna and then de-rate it down to 64.6 watts ERP, look at the license further. It was for an STA (Special Temp Authority) with special permission from the 800 MHZ re-banding organization in 2017. It was for San Diego County for a facility in Imperial County. Just a guess but I think it was a range testing gap filler station cobbled together from available equipment . My guess from afar and you SO CAL members will know much more.

 

[lenk911]

Do you have a blog or podcast?

No. Just experience since 1968 engineering high value communications systems.

 

[speedway_navigator]

No. Just experience since 1968 engineering high value communications systems.

Well than dag nabit start one...

 

[cavmedic]

This one was kind of funny: WQZU353 has 100 W out, 64.6 W ERP.

That could also be what was requested / submitted vs what was actually coordinated and licensed .

I have a pair that was requested 300w but am limited to 115 W ERP at a particular site and shows similar for that location.

 

[AM909]

This one was kind of funny: WQZU353 has 100 W out, 64.6 W ERP.

That could also be what was requested / submitted vs what was actually coordinated and licensed .

I have a pair that was requested 300w but am limited to 115 W ERP at a particular site and shows similar for that location.

I was just commenting on the absurd implied precision of 0.1W (0.15% of 64.6W). Bird 43 has a precision spec of 5% full-scale and Telewave 44x is 6–10%.

 

[speedway_navigator]

And the fine for having 64.7 W is probably $10,000.0000