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RT97S repeater broken or silent when transmitting greater than 1000 ft away


Skinnerfam95
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Hi, I purchased the RT97S from myGMRS.com.
 
I'm having issues as follows.
 
My repeater settings:
- Using the 650 frequency pair
- ENC/DEC CTCSS codes to OFF on the repeater 
- SQL is set to 1
- Transit function is ON
- W/N is set to WIDE (matches the radios)
- TX Power is set to HIGH
 
The repeater antenna is 20FT high, a gain of 7dB, and SWR of 1.3/1.8 respective to the frequency pair.
 
I'm using Radioddity GM-30 (5W) radios.  For a simplex baseline using two GM-30 radios:
- At 3 miles apart I get crystal clear both ways 
- One radio is using the repeater antenna
- The other radio is using a mobile mag mount roof antenna
 
When using the repeater with the transmitting radio is line of sight less than 500 feet from the repeater everything seems to work ok.
-- I've received clear transmissions from a receiving radio as much as 8 miles away line of sight away from the repeater so long as the transmitting radio is less than 500 feet from the repeater.
 
I am having limited success transmitting at 1000 feet away line of sight.
- Radios that are less than 500 feet from the repeater hear the transmission of the radio that is 1000 feet away clearly
- Other radios at 1000 feet from the repeater hear the transmission broken
- The tail tone (burst of white noise) comes through strong on all radios
- It appears to me that the transmission is degraded only when repeating the transmission of a radio 1000 feet or more away.  The tail tone is after the transmission has completed and comes through strong
 
Transmitting radios over 1000 feet from the repeater have worse symptoms than described above.  It is unusable.
 
Please help.

Thanks,
Matt
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Hi, I purchased the RT97S from myGMRS.com.   I'm having issues as follows.   My repeater settings: - Using the 650 frequency pair - ENC/DEC CTCSS codes to OFF on the repeater  - SQL is set to 1 - Transit function is ON - W/N is set to WIDE (matches the radios) - TX Power is set to HIGH   The repeater antenna is 20FT high, a gain of 7dB, and SWR of 1.3/1.8 respective to the frequency pair.   I'm using Radioddity GM-30 (5W) radios.  For a simplex baseline using two GM-30 radios: - At 3 miles apart I get crystal clear both ways  - One radio is using the repeater antenna - The other radio is using a mobile mag mount roof antenna   When using the repeater with the transmitting radio is line of sight less than 500 feet from the repeater everything seems to work ok. -- I've received clear transmissions from a receiving radio as much as 8 miles away line of sight away from the repeater so long as the transmitting radio is less than 500 feet from the repeater.   I am having limited success transmitting at 1000 feet away line of sight. - Radios that are less than 500 feet from the repeater hear the transmission of the radio that is 1000 feet away clearly - Other radios at 1000 feet from the repeater hear the transmission broken - The tail tone (burst of white noise) comes through strong on all radios - It appears to me that the transmission is degraded only when repeating the transmission of a radio 1000 feet or more away.  The tail tone is after the transmission has completed and comes through strong   Transmitting radios over 1000 feet from the repeater have worse symptoms than described above.  It is unusable.   Please help.
Thanks, Matt


Good Day Matt.

Your symptoms are indicative of desense, most likely caused by incorrect adjustment of the repeater’s duplexer. The purpose of the duplexer is to prevent leakage of the repeater’s transmit signal back into the repeater’s RF input. If it leaks in it will drown out/cover up/mask the signal received from your HTs and other radios trying to use the repeater.

To achieve optimum performance, the duplexer must be calibrated for the specific frequencies that your repeater is set to operate on. When repeater frequencies change, the duplex has to be re-tuned/calibrated for the frequencies in use. So although your repeater can change is frequencies, a duplexer needs to be recalibrated for each change.

I cannot speak to what frequency pair your particular duplexer might have been tuned for at the factory, or even it was tuned at all. But your symptoms strongly suggest it is not the 650 frequency pair. But even if it was once tuned for 650, changes caused by jostling in transit could have thrown it out.

In order to tune the duplexer yourself you will need to possess the knowledge and test equipment to do so. If you do not have both, then you will need to seek out a person that does. A radio service shop or an amateur radio operator that actively maintains repeater sites are both candidates for this. A precision lab-grade VNA is the typical instrument required for doing this.

On the net you will find many videos that cover duplexer tuning, so the procedure is well documented. The fabulous but inexpensive NanoVNA does not perform well enough to calibrate a duplexer optimally. However, according to a recent YouTube post, In the hands of an experienced skilled operator, it appears that perhaps the $200 NanoVNA v2Plus4 might be able to help one get pretty close.

Hope this helps.
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I was thinking desense as well, but was going to ask if you're using two hand-held radios to do your testing. For example, are you transmitting on one while trying to listen on the other? If so, their proximity to each other could be causing desense in the receiving radio, which would make it look like the repeater isn't working. If you're doing the testing by yourself, you'll likely run into this issue.

If possible, you'll want to get a family member (or another licensed GMRS user) to listen somewhere within range of the repeater as you move about testing it. They could then reply as you check in from various locations.

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3 hours ago, WyoJoe said:

I was thinking desense as well, but was going to ask if you're using two hand-held radios to do your testing. For example, are you transmitting on one while trying to listen on the other? If so, their proximity to each other could be causing desense in the receiving radio, which would make it look like the repeater isn't working. If you're doing the testing by yourself, you'll likely run into this issue.

If possible, you'll want to get a family member (or another licensed GMRS user) to listen somewhere within range of the repeater as you move about testing it. They could then reply as you check in from various locations.

Hi, thanks for the reply.  Let me see if this adds anything to what you're thinking.

One of the tests I similar to what I was describing... there are two HT's. 

One HT is 1000FT away with line of sight to the repeater antenna. 

The other HT inside the house on the first floor.  It is about 20 feet from the repeater and about 70FT from the outdoor repeater antenna.

The repeater is in my basement with a 100FT LMR400 feedline to the outdoor antenna (on a 20FT tall pole) which is about 60FT from the repeater.

I think that should rule out the desense between the HTs/repeater.

Please let me know if I'm missing something about the concept.

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6 hours ago, mbrun said:

 


Good Day Matt.

Your symptoms are indicative of desense, most likely caused by incorrect adjustment of the repeater’s duplexer. The purpose of the duplexer is to prevent leakage of the repeater’s transmit signal back into the repeater’s RF input. If it leaks in it will drown out/cover up/mask the signal received from your HTs and other radios trying to use the repeater.

To achieve optimum performance, the duplexer must be calibrated for the specific frequencies that your repeater is set to operate on. When repeater frequencies change, the duplex has to be re-tuned/calibrated for the frequencies in use. So although your repeater can change is frequencies, a duplexer needs to be recalibrated for each change.

I cannot speak to what frequency pair your particular duplexer might have been tuned for at the factory, or even it was tuned at all. But your symptoms strongly suggest it is not the 650 frequency pair. But even if it was once tuned for 650, changes caused by jostling in transit could have thrown it out.

In order to tune the duplexer yourself you will need to possess the knowledge and test equipment to do so. If you do not have both, then you will need to seek out a person that does. A radio service shop or an amateur radio operator that actively maintains repeater sites are both candidates for this. A precision lab-grade VNA is the typical instrument required for doing this.

On the net you will find many videos that cover duplexer tuning, so the procedure is well documented. The fabulous but inexpensive NanoVNA does not perform well enough to calibrate a duplexer optimally. However, according to a recent YouTube post, In the hands of an experienced skilled operator, it appears that perhaps the $200 NanoVNA v2Plus4 might be able to help one get pretty close.

Hope this helps.

 

Hi, thanks so much for your comments.

Interesting option of the upgraded NanoVNA.  Are you aware of an equally cost effective tracking generator??.. or is there an alternate method that doesn't require a tracking generator?

I did a quick test and found the least amount of noise on the first channel.  I put a dummy load on my repeater with two HTs in the same room- I'm may not be thinking right, but I want as much desense and noise as possible to compare the 8 channels and see which is the best. 

I'm going to try some 1000ft or more range tests tonight with the radios properly separated.

The interesting thing is that is not well marketed by myGMRS or Retevis.  Retevis offers a custom tuned duplexer option as well an explicitly GRMS 8 channel option.  The GMRS option does not indicate choosing a frequency/channel at purchase.  The repeater was preloaded with all 8 channels.

You confirmed what little I do know about duplexers.  I should have asked the question about how all 8 channels work before jumping in and buying it. :)

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When I ordered my RT-97 from Radioddity directly, I specified the frequency pair I wanted to use (442.975). Radioddity's technicians tuned the duplexer to my chosen frequency pair. I never bothered to program any other frequencies as I knew the duplexer would not pass even a frequency only 0.25 MHz +/- higher or lower.

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Hi, thanks so much for your comments.
Interesting option of the upgraded NanoVNA.  Are you aware of an equally cost effective tracking generator??.. or is there an alternate method that doesn't require a tracking generator?
I did a quick test and found the least amount of noise on the first channel.  I put a dummy load on my repeater with two HTs in the same room- I'm may not be thinking right, but I want as much desense and noise as possible to compare the 8 channels and see which is the best. 
I'm going to try some 1000ft or more range tests tonight with the radios properly separated.
The interesting thing is that is not well marketed by myGMRS or Retevis.  Retevis offers a custom tuned duplexer option as well an explicitly GRMS 8 channel option.  The GMRS option does not indicate choosing a frequency/channel at purchase.  The repeater was preloaded with all 8 channels.
You confirmed what little I do know about duplexers.  I should have asked the question about how all 8 channels work before jumping in and buying it.


You are not like the first to order or build their first repeater without full awareness of duplex. Live and learn. There is much available on the net regarding them.

Most repeater radios can be programmed for a wide range of frequencies, the RT97 is no exception. Duplexers are not software controlled. They are tuned circuits that require good-old-hands-on calibration by a skilled technician.

The VNAs I know of include a tracking generator. The signal generated by the VNA gets passed through the duplexer and then back to the VNA to be analyzed. So there is no need for an external tracking generator.


Michael
WRHS965
KE8PLM
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100' of LMR 400 is not helping in UHF. At 450mhz its roughly 2.7db at 100'. That about takes half your power away (3db is half.) At 5 watts out of the transmitter (if the duplexer is tuned correct, you are at 2.5 watts before you hit the antenna. Add in any adapters you may have and your even less. If you have your watt meter I'd test power leaving the repeater and also if possible hitting the antenna. 

I would verify your duplexer is tuned for the channel you are testing and attempt to get the antenna way closer to the antenna if you want this to perform well. 

https://www.pasternack.com/images/ProductPDF/LMR-400.pdf

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7 hours ago, kb2ztx said:

100' of LMR 400 is not helping in UHF. At 450mhz its roughly 2.7db at 100'. That about takes half your power away (3db is half.) At 5 watts out of the transmitter (if the duplexer is tuned correct, you are at 2.5 watts before you hit the antenna. Add in any adapters you may have and your even less. If you have your watt meter I'd test power leaving the repeater and also if possible hitting the antenna. 

I would verify your duplexer is tuned for the channel you are testing and attempt to get the antenna way closer to the antenna if you want this to perform well. 

https://www.pasternack.com/images/ProductPDF/LMR-400.pdf

Hi, thank you for the comment.

If able, please comment on my baseline testing approach.  Given the details below, I expect that the repeater should perform as well or slightly better than the simplex HT baseline test.  If this works out the repeater will likely have less than 25 feet of LMR400 and an antenna that is better tuned for GMRS.

I'm using Radioddity GM-30 HT's- advertised 5W, but shows 4.1W forward power on my "budget 120W power meter" to a dummy load with no feedline.

The repeater RT-97S is advertised 10W (sometimes 5W depending where you look)... shows 6.4-6.6W forward power (measuring each of the 8 channels) on my "budget 120W power meter" to a dummy load with no feedline.  That said, I need to do more study of the duplexer because all 8 channels pass similar forward power.

With the HT's for my simplex baseline test I use the same antenna as the repeater tests (20 ft pole w/100 ft of LMR400).  The distant HT is using a mag mount Nagoya NMO-200C.

With the HT simplex test I'm getting generally 3 miles in this configuration depending on the direction w/ varying terrain... and over 10 miles as I climb in elevation.

The 100 feet of LMR400 is a necessary evil to my ham shack being in my basement.  I'm also using a Diamond X50A for the antenna for convenience of testing.  The spec does not include the GMRS frequencies, but it has decent resonance based on my NanoVNA analysis. 

The discussion of 1000 FT is just because of the poor repeater performance.

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The concern over the loss in the feed-line is secondary, IMO, until the duplexer issue is put to bed.

I love the fact that you are doing simplex tests first using low power HT and the exact antenna system (feed-line and cable) that you’ll be using with the repeater. This is a good way to establish your best case scenario. I would advocate that approach to anyone considering installing a repeater.

I do not expect the RT97 two-way line of site range to equal what you can achieve doing simplex, even when the duplex is adjusted as best as is possible. The duplexer is the limiting factor. However I would expect dramatically better Rx range than the 1000ft you have indicated you have achieved thus far. Owners and users of the RT97 are better qualified to offer real-world distances they have achieved. There is one member on this forum that has one installed in Alaska, operating on battery and solar power. I believe 10-20 miles or more have been achieved.


Michael
WRHS965
KE8PLM

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Thanks again everybody for all the comments.  I contacted Retevis and they referred the issue to Rich at myGMRS.com (which is where I purchased it).  I'm waiting for his reply before I open it up.  After watching some youtube videos I've order an "authentic" NanoVNA V2 Plus4-- FEDEX from China.. so I don't know how long that will be.

I do have a NanoVNA H that I'm curious if it will give any indication... I certainly wouldn't attempt to tune it with this VNA.

After I hear back from Rich I'm going to reach out to my ham club and/or a local GMRS repeater club to see if someone has the gear and the time to help me out.

I'll post back here incase someone else ends up chasing the same issue.  The only thing I hate more than a thread that dies before it's answer is the thread that just said "I got it working".  Haha

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Ok... I wanted to give an update.  I bought this RT97S from myGRMS.com.  Rich immediately offered to replace it.

I wanted to do at least another test... but in my preparation to send it back I grabbed the box.

I discovered the sticker was on the box indicating it was tuned to 550.  This may come down to Read The Flippin Box.

I'm going to test 550 tonight or tomorrow night and will post back the results.  The elevation profile below is "6.4 miles, channel 15, simplex using 5W HTs" test.  One side had the stock rubber duck and the other side had a 35" mag mount.  It was near the limits of the 5W HTs given the terrain. 
 
I'm going to setup the 550 test of the repeater in the same location, but I'll use a mag mount on the repeater side instead of the rubber duck.
 
I've only attempted long rage tests on 650 (arbitrary, fairly vacant frequency in my area) and 725 based on my 300ft dummy load test.

I tested all 8 channels at about 300ft with a dummy load... I did hear variations of quality.. but nothing stood out.  I didn't take good notes.. but as I recall 550 had most static noise, 725 had the least noise.

 

sticker.png.54e24d49b70658d8f23903bdd7a766e4.png

elevation.png.84e8f5343f5676cd53661dc4d37b983f.png

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The notches on even high end BpBr duplexers are actually wide enough for GMRS that you have some channel flexibility, let alone the Fumei/Jesai notch only duplexers that come with the RT97; GMRS is only 175Khz wide (195khz if you account for signal bandwidth) for the whole slice of spectrum. While you'll have best performance on one channel, it should be wide enough to allow you to move around without a massive impact.

What you're describing does sound like desense - either that duplexer was not tuned right, or it's not providing enough isolation; you really want 80dB or more - I've typically seen about 50-60 dB isolation on the Jesai/Fumei duplexer units with 4-5db insertion loss; both hurt your receive performance.

Also on repeaters; feedline and antenna can make a tremendous impact - cheap feedline or antenns can generate wideband noise when transmitting. On a normal base station, that's not really a problem, on a repeater where you're trying to listen while transmitting at the same time, that can be an issue. Think of it as you setting up a microphone to hear a pin drop from across the house while your neighbor is testing out a trunk full of subwoofers. LMR400 can be noisy over time, although freshly installed tends to be ok.

 

Edited by JeepCrawler98
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18 hours ago, JeepCrawler98 said:

The notches on even high end BpBr duplexers are actually wide enough for GMRS that you have some channel flexibility, let alone the Fumei/Jesai notch only duplexers that come with the RT97; GMRS is only 175Khz wide (195khz if you account for signal bandwidth) for the whole slice of spectrum. While you'll have best performance on one channel, it should be wide enough to allow you to move around without a massive impact.

What you're describing does sound like desense - either that duplexer was not tuned right, or it's not providing enough isolation; you really want 80dB or more - I've typically seen about 50-60 dB isolation on the Jesai/Fumei duplexer units with 4-5db insertion loss; both hurt your receive performance.

Also on repeaters; feedline and antenna can make a tremendous impact - cheap feedline or antenns can generate wideband noise when transmitting. On a normal base station, that's not really a problem, on a repeater where you're trying to listen while transmitting at the same time, that can be an issue. Think of it as you setting up a microphone to hear a pin drop from across the house while your neighbor is testing out a trunk full of subwoofers. LMR400 can be noisy over time, although freshly installed tends to be ok.

 

The test of 550 only worked up to about 1400 feet with 5W HT to the repeater both using mag mount antennas-- so 550 did not resolve the distance issue. 

Another point of interest is I also have a 25W mobile GMRS radio.  At the 1400 feet distance it only worked on low power- medium and high didn't open the repeater.

Rich commented "the higher power should work better as it would be overcoming the loss in the duplexer better".  He asked if there could be an issue with 25W mobile.  I don't think so at this point, but I'll add this to my list to investigate further.

I sent the repeater back to Rich this morning.  Hopefully, he'll let me know what he finds out when he looks at it himself.

Thanks again for all the comments.

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On 12/13/2021 at 2:00 PM, Skinnerfam95 said:

 

The 100 feet of LMR400 is a necessary evil to my ham shack being in my basement.  I'm also using a Diamond X50A for the antenna for convenience of testing.  The spec does not include the GMRS frequencies, but it has decent resonance based on my NanoVNA analysis. 

 

Can you post a sweep of the X50A through 462-468?

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