GR300 UHF repeater help

[hfd921]

Hi,

I have some technical questions, heres the situation we acquired a GR300 mobile UHF repeater and a frequency. We have set up the repeater in the garage area of the building. We ran a coax cable up an existing tower about 50 feet and mounted a fiber glass UHF antenna tot he tower.

Well near the site everything works ok, we work off of portable radios. Now I've notice we are getting almost the same amount of range on simplex as we are on our repeater. Now I'm no radio guru , but something is wrong here.

Also i've noticed when the guys try to key up it cuts them off and the repeater rekeys up, the reason i know this is because the courtesy beep rekeys up a couple times, while there transmitting. The traffic is like hit or miss, i would think the GR300 would operate better we are on portables but we are only talking like a 2 mile range.

Can you guys help me out, Suggestions, quick fix any input..................


Any ideas ???????????????????



I'm at 50 feet on the tower , do i need to go higher?

Does the tower need to be grounded better?

Do i need a better antenna? ( currently have a 100$ Fiberglass UHF antenna)

**** What would be the best antenna to buy for max range???????

Do i need to get rid of the courtesy beep DTMF?

Is there some type of programming on the gr300 i might be missing?

Is the PL tone incorrect or something? (could this be the issue)

Should we remove the PL tone? ( no one has the frequency and no one uses UHF around us)

Should the repeater be indoors ( what room temperature is to warm for the Gr300 to be placed?

[Will]

Step One: make sure the duplexer is tuned correctly, seems you have desence.

What kind of coax cable? How long?

100S antenna ?????

What is the area of operation? Urban or out back?

"we acquired a GR300 mobile UHF repeater and a frequency. " ???????????

[Bill_G]

I agree with Will - duplexer. Or a really bad coax and/or antenna. Or all of the above.

[hfd921]

Step One: make sure the duplexer is tuned correctly, seems you have desence.

What kind of coax cable? How long?

100S antenna ?????

What is the area of operation? Urban or out back?

"we acquired a GR300 mobile UHF repeater and a frequency. " ???????????

Iam not sure of the type of coax, but its about 100 foot, we operate in an urban area.

So the dulexer might be bad?

or just needs retuning?

[Bill_G]

Yep. The duplexer could be tuned incorrectly, or it could be bad, or the something in the transmission line from the connector at the duplexer all the way up to the antenna could be bad. Most likely, based on how you describe it is working, the duplexer is tuned wrong. There is also the possibility someone connected the TX/RX ports on the duplexer to the wrong ports on the radio.

[hfd921]

I was told possible changing the receive radios squelch on the Gm300, would help out and make the repeater work better., i was explained it would receive transmissions better , so a better signal Rx better it can be Tx,

adjust the squelch? yes / no.... a little all the way?

[WB6DGN]

What KIND of transmission line; RG-8? RG-58? LMR400? Heliax (what size?)?

Didn't see previous comment about coax type. Need to know that; that alone could be the problem. At UHF frequencies, you need good quality, low loss transmission line. In my opinion the absolute minimum for a 100' run would be 1/2 inch Heliax with 7/8 inch much preferred. Anything less is only good for short jumpers.
Tom

[Bill_G]

I was told possible changing the receive radios squelch on the Gm300, would help out and make the repeater work better., i was explained it would receive transmissions better , so a better signal Rx better it can be Tx,

adjust the squelch? yes / no.... a little all the way?

Better is a subjective term. It sets the threashold for the receiver to open, but the overall quality of the receiver remains the same. And the squelch setting would not explain the problems you are having.

[Will]

I was told possible changing the receive radios squelch on the Gm300, would help out and make the repeater work better., i was explained it would receive transmissions better , so a better signal Rx better it can be Tx,

adjust the squelch? yes / no.... a little all the way?

NO.

Get the duplexer and antenna straightened out first.

[WV8VFD]

If the duplexer tuning wasnt checked before it was installed it is a good possibility it got bumped out of tune in transit. Helping a buddy of mine with a few installs there have been times we have had the duplexer perfectly tuned at the shop, but by the time we drove from the shop up to the tower sites, it has lost its tune from the bumps along the way.

[AEC]

You need to lock the tuning rods before movement.
Who made the duplexer?
TX/RX, EMR, Sinclair...?
Changing PL/DPL codes on the portables will not help with the repeater, that is an entirely separate issue of its own.
Sweep the feedline, check connectors,Check antenna return loss(VSWR) and retune the duplexer.
If it is a Band Pass/Band reject, you have adjustable capacitors in each cavity to 'notch' the offending signal, both in TX and RX. You tune the TX cans, set the notch to reject the RX signal, same goes for RX, as you tune for max RX signal, and 'notch' out the transmit with those caps. They should have covers on them, spin off with fingers.
Most have 4, 2 for each side(tx/rx).
Once the cavities are tuned properly, check every other aspect of the system, from the antenna back to ensure everything is in proper operation.
Loss is of great importance on UHF, and every dB does make a big difference, especially on receive. If too much transmitter noise is getting into the receive sectionof the duplexer, it will wipe out the receiver, and I suspect this is THE issue that affects your system more than all the other problems, but might not be the ony problem.
Any attempt to install a GaAsFET preamp on your system will be a waste of money, as any amount of signal getting in will destroy the active device in the preamp.
You should see 3dB or less insertion loss with most duplexers. Typical loss is just over 1.5 dB per section, depending how the couplng loops are configured. Higher insertion loss increases the depth of rejection, and less insertion loss lowers the rejection of the cavities. Check the TX/RX website for more information on how to propely tune a cavity duplexer, it will help you understand how things need to be done in order to increase system performance.
If you are located at a crowded site, consider a single or dual section ferrite isolator for your transmit side.

[WV8VFD]

You need to lock the tuning rods before movement.

We did. But the instances of this happening were tower sites you had to baja to get to.

[motorola_otaku]

General suggestions:

• If you bought a duplexer off Ebay from Hong Kong like one of these then I can guarantee you 100% that it wasn't tuned properly. You need to take it to someone with a spectrum analyzer/tracking generator combo and have them tune it properly for your frequencies.
• You cannot use any kind of braided coax on a repeater antenna - even if it seems like it's working okay to begin with you'll develop problems with noise, desense, and/or intermod (squeeeeeeal) over time. You have to use corrugated cable, like Andrew Heliax or one of its variants.
• Small fiberglass antennas in the 0-6 dB gain range typically make poor repeater antennas. "Ringo" and "J-pole" antennas are totally unsuitable for repeater use. Both will cause the same problems that braided coax causes over time. Look for a good used folded dipole array antenna, or a "green stick" fiberglass antenna from Andrew Decibel, Telewave, etc.
• If the antenna is side-mounted on the tower, it needs to be at least 2 feet out for UHF to get decent omnidirectional radiation.

[hfd921]

General suggestions:

• If you bought a duplexer off Ebay from Hong Kong like one of these then I can guarantee you 100% that it wasn't tuned properly. You need to take it to someone with a spectrum analyzer/tracking generator combo and have them tune it properly for your frequencies.
• You cannot use any kind of braided coax on a repeater antenna - even if it seems like it's working okay to begin with you'll develop problems with noise, desense, and/or intermod (squeeeeeeal) over time. You have to use corrugated cable, like Andrew Heliax or one of its variants.
• Small fiberglass antennas in the 0-6 dB gain range typically make poor repeater antennas. "Ringo" and "J-pole" antennas are totally unsuitable for repeater use. Both will cause the same problems that braided coax causes over time. Look for a good used folded dipole array antenna, or a "green stick" fiberglass antenna from Andrew Decibel, Telewave, etc.
• If the antenna is side-mounted on the tower, it needs to be at least 2 feet out for UHF to get decent omnidirectional radiation.

Do i even need to have a PL tone on our repeater, frequency ??????????????????

[Bill_G]

Do i even need to have a PL tone on our repeater, frequency ??????????????????

Have to? Technically no. Legally yes. I think you must exercise some access control over a repeater, but I yield to those more familiar with FCC rules.

Want to? Yes. It's good practice. There might be other people on the channel. Might even be some other repeaters. What a mess that would make if they attempt to key their repeater and get two because yours keyed up on top of theirs. If you did nothing about it, that would be willful interference.

[hfd921]

I just found out this information , i feel rather stupid but could this be the problem.????

The owner of the gr300 repeater prior to me was only licensed for 2watt operation per the fcc, i saw this on a fcc search of their old frequency. The unit was just for their job sites(to be portable). So if the Gm300's in the unit are set to 2watt could this be the reason for our horrible range??????


I'm no radio expert but it makes sense now, 4 watts going in and then 2 watts shooting back out definitely can't be good. We have a good working gr300 and a good antenna which is 50 feet off the ground.

Any input?????????

[Bill_G]

There are a lot of 30w repeaters running on 2w licenses. Have you measured the power? Maybe you should hire a local radio shop to go over your equipment.

[PETNRDX]

Look at the model number on the TX radio.
If it is a LPI model, the second digit will be an 0 ( zero )
Should be something like M04GMC20D1Ax for a 1 to 10 watt.
A 10 to 25 watt would be M34GMC20D3Ax
A 25 to 40 watt would b3 M44GMC20D3Ax
As the post above says, lots of those have the higher power radio installed.
But, if it is really running two watts, you probably want to up that something more, in addition to solving the duplexer, feedline and antenna questions.

[N4KVE]

If the tx radio is actually 4 watts, you might be lucky & the receive radio could be 25 watts. Just swap them, & reprogram. Sometimes this happens, Cross your fingers. GARY N4KVE

[HLA]

just curious but what are the freq's for the repeater? And you did have your portables programed for it right? The repeater might be set for low power but you make it sound like you just bought a repeater and put it up but didn't alter your portables to both freq's to work with the repeater? And did you apply for a license?

[hfd921]

I have a question im told there is a setting on the gr3oo, gm300's i was told there is Local (low power) and Distant (high power). I think our repeater is set to Local (low power) which would explain the short range. How much should Distant (high power) get me, more range?

[Bill_G]

The local / distant setting (if yours has one) is in the receiver settings, not the transmitter. It adds a little attenuation to the rx front end in local, removes it in distant. Whether it benefits you or hurts you would have to be determined by a tech with test equipment.

A receiver has to do two things - receive the frequency of interest, and reject all others. The local / distant switch helps with rejection. For example - if your repeater antenna is at a very quiet site with no interference from other transmitters in the area, you might be able to get away with selecting distant. You will get a few more db of sensitivity that may make that last mile you need. On the other hand, if you are at a shared site with several other transmitters, your receiver might be effectively deaf in distant mode. Adding some attenuation in local mode would lower the noise floor and increase your effective sensitivity.

Again, it would have to be determined by a trained tech that understands the difference.

Have you sorted out your duplexer / coax / antenna problems yet?

[GlennD]

There are a lot of poorly tuned duplexers out there. On a properly tuned unit all of the tuning rods on each side should be about the same length. I can not tell you how many duplexers I have seen miss-tuned.
Do not ever tune the unit under power. Use at the minimum a service monitor with a tracking generator.

[Will]

Again, it would have to be determined by a trained tech that understands the difference.

And what the repeater IS licensed for.

[Bill_G]

Again, it would have to be determined by a trained tech that understands the difference.

And what the repeater IS licensed for.

?

The license wouldn't affect the receiver, site noise, or the local / distant setting. OTOH, it's pretty obvious hfd921 needs some assistance with the hardware. Making sure he is properly coordinated is probably not a bad idea.