Horrible Interference on repeater

[12dbsinad]

With 5 repeaters at the same site it might be better to use a master receive antenna with window filter and preamp then transmitter combiners to feed the other antenna. Total cost will probably be less than using duplexers with separate antennas and performance can be very good.

Yea, if he wants to put out about 5 watts per repeater due to combiner loss. He'd probably need to add some external amps to those repeaters. Combiners are great but very losey and inefficient.

 

[jcefd10]

Yea, if he wants to put out about 5 watts per repeater due to combiner loss. He'd probably need to add some external amps to those repeaters. Combiners are great but very losey and inefficient.

Yeah, our coverage diminished quite a bit when the combiner was installed.

 

[prcguy]

Yea, if he wants to put out about 5 watts per repeater due to combiner loss. He'd probably need to add some external amps to those repeaters. Combiners are great but very losey and inefficient.

It all depends on channel spacing. If the transmit channels are less than 300KHz apart then you would have to use hybrid combiners and you can loose maybe 7dB through a 4 channel combiner. If the spacing is more than 300KHz you can get close to 1dB loss using a single cavity/single isolator type.

You can also use a combination like if two of the five transmitters are close spaced you can combine them using a hybrid then into cavity/isolator with the rest of them. That one pair might loose over 3dB power but the rest can be a little over a dB. So you start with 100w transmitters and a couple of channels are at 40w to the antenna and you can turn down the other transmitters to 60w and they will all be close in power at the antenna.

The last time I used a hybrid type it was to combine an analog/P25 repeater on the same frequency as a Yaesu Fusion at the same site. It worked out great with about 40w out to the antenna from each repeater.

 

[speedway_navigator]

I'm assuming you will never have any water intrusion with the power supply on the floor.

 

[jcefd10]

I'm assuming you will never have any water intrusion with the power supply on the floor.

You’d be assuming correctly.
That’s a backup that was used once after a lightning strike.

 

[jeepsandradios]

Dealing with similar issues in a similar band. Quick tests for me was my SA on the receive multicoupler. Once I had the frequency narrowed down I used an SDR RTL and both SDR trunk and the SA tool from airspy. In 10 minutes I was decoding DMR ID's on my laptop. Some digging found it was an agency 150 miles away. VHF sucks. As was mentioned you need to check for any splinter channels also. I would think someone with a decent SA can narrow down the signal pretty quick. It will take time but a day at the site should put you in a direction. If you just seeing local noise floor raised up that can also cause your issue so double check all componants. Really without a good SA on site its all speculation. Need to see whats really there.

 

[MTS2000des]

Every agency in South Georgia deals with this on VHF, as is mentioned, signal identification is key. Would not be surprised if it's tropo from Florida or Alabama this time of year. The FCC is a joke and doesn't care. When 6 of my 12 channel 800MHz simulcast system in metro Atlanta were being jammed by a rogue BDA, they barely did anything. You are on your own to do the detective work and find the culprit.

 

[kb5udf]

You might want to have a look at this VHF propagation map, to see if enhanced propagation and from where correlates with your interference problem VS if there seems to be no relationship.

Regarding the request for upload, sorry, for some reason it did not load when I first viewed your post.

VHF Propagation Map

vhf.dxview.org

 

[jcefd10]

I'll be able to nail it down hopefully Monday. That's when I'm upgrading the freq pair at another site and will have someone with a decent SA and test monitor with me. Reading all the replies here only lets me know that I have A LOT to learn.

 

[jcefd10]

You might want to have a look at this VHF propagation map, to see if enhanced propagation and from where correlates with your interference problem VS if there seems to be no relationship.

Regarding the request for upload, sorry, for some reason it did not load when I first viewed your post.

VHF Propagation Map

vhf.dxview.org

That map, if correct, really backed up the station I was thinking may be the culprit. It's in Geneva AL, and from what one of the guys I spoke to yesterday told me, they are running a pretty high power, on a Nexedge 9600 system. But I'll know more Monday

 

[jcefd10]

Every agency in South Georgia deals with this on VHF, as is mentioned, signal identification is key. Would not be surprised if it's tropo from Florida or Alabama this time of year. The FCC is a joke and doesn't care. When 6 of my 12 channel 800MHz simulcast system in metro Atlanta were being jammed by a rogue BDA, they barely did anything. You are on your own to do the detective work and find the culprit.

Hopefully I'll be able to nail it down next week. Today it hasn't been too bad so far.

 

[AM909]

Keep in mind that on days like today, when it "hasn't been too bad", you're looking for a signal that might be as low as -100 dBm to -120 dBm, which takes a pretty decent spectrum analyzer or some other tricks. Pretty shocking to see these high-band situations where they co-ordinate and license base transmitters within potential range of other systems' base receivers on the same freqs.

 

[jcefd10]

Keep in mind that on days like today, when it "hasn't been too bad", you're looking for a signal that might be as low as -100 dBm to -120 dBm, which takes a pretty decent spectrum analyzer or some other tricks. Pretty shocking to see these high-band situations where they co-ordinate and license base transmitters within potential range of other systems' base receivers on the same freqs.

I did swing by the site when I went to town earlier and it is still coming across. Just not as strongly.
When applying for a new pair of frequencies for our secondary site we had to send the frequencies back and request new ones 3 times before we finally got a good pair. We also had to use 6.25 on this new pair, which is fine by me.

 

[AM909]

...We also had to use 6.25 on this new pair, which is fine by me.

There's that issue, too. I didn't look at the complete picture of the adjacent channels, but NXDN "narrow" is supposed to be 8K30F*, which doesn't quite fit in 7.5 kHz channel spacing. I would think the 4K00F* NXDN "very narrow" would be a requirement, barring some special situation. When you're on the newer "split" channel between the older 15 kHz channels, I'd expect a lot of difficulty from the legacy users on those.

 

[mrsvensven]

Because this interference seems to have been narrowed down to another LMR user and not some other source, you can try reporting it to APCO. APCO has some sort of MOU with the FCC to handle interference complains between two LMR users so that the FCC doesn't have to deal wih them. I don't know what authority APCO actually has to do anything except request that one user gets a new frequency (possibly at your cost)

Interference Reporting

 

[speedway_navigator]

Interesting to see WQPP657 is 50 W TPO and 300 ERP but some other licenses are 60-180 and 110-250.
I've always wondered why TPO is listed since ERP seems to be the limiting factor.

Our county has some paging freqs at 25-34.4 and 100-169.8.

JCEFD10 - have you heard a call sign? I think 90.245 would be applicable for this site.

 

[G7RUX]

Good evening all.
I have a very general question here. Here recently we have been having some pretty bad issues with interference on one of our repeaters. We have 5 in the same hut, and only 1 is getting the interference.

Something I would suggest doing would be to take all of the transmitter frequencies on the site and pop them into the process for calculating related intermods…you may be surprised as a lot of this sort of issue are caused by either generation in the receiver, another transmitter on site or perhaps in rusty junctions in metalwork on site.

 

[jcefd10]

Today was the day.
Got the 2 guys up at the tower site to see if we could nail down the interference, and whaddaya know, it would not rear its head. It came across very slightly for just a minute, then gone.
They did test for intermod from the other repeaters and the combiner and all tested great. Swept the coax and antenna, good as well.
We stayed up there for a good hour waiting to catch any of the transmissions and couldn't get anything at all.
So for now, all is good. If it keeps getting as bad as it was, the only thing we came up with is to apply for a new pair of frequencies.

 

[jcefd10]

Interesting to see WQPP657 is 50 W TPO and 300 ERP but some other licenses are 60-180 and 110-250.
I've always wondered why TPO is listed since ERP seems to be the limiting factor.

Our county has some paging freqs at 25-34.4 and 100-169.8.

JCEFD10 - have you heard a call sign? I think 90.245 would be applicable for this site.

I heard not a single thing except what sounded like that data. I could not identify anything at all, so it was solely a guessing game.

 

[jeepsandradios]

If yo uhave a network connection at the site a NUC or small PC with a RTL hooked to your multicoupler or RX port is a cool thing to have. Thats what I did at 2 sites so when the interfearance starts up I can get in and look at the signal remotely. I think I have $150 into each box. May be something to think about.