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Retevis RT97 GMRS Repeater with "mouse" ears


JeremiahBarlow
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Hey, somewhat new to radios and repeater tuning.

After getting my GMRS approval, I purchased a simple repeater here:   https://www.retevis.com/rt97-portable-gmrs-repeater-mobile-repeater?utm_source=GA&utm_medium=AD_K&utm_campaign=RT97&gclid=Cj0KCQjw0umSBhDrARIsAH7FCoefvNzaDiFF1Wj9bfswXlGTClsKp-DKQBf_nJAnSMcuh8SqChgp-4YaAkc3EALw_wcB#A9150CX1-C9196AX1-C9123AX1

Then I mounted it on my brother's 25' Rohn tower and connected it all up,,,,but ...

I have to be within a 300 feet of the repeater to get it to receive any signal.   It transmits fine but has trouble receiving.   We are using Baofeng UV-9R and they are connecting with each other at farther distances than the repeater can receive.   It seems quite frustrating for common knowledge.   I need someone with more wisdom to help me out.

I believe one of the follow could be the issue:

  • The antenna could be faulty .... (not likely because it was a good quality looking, however I haven't ruled that out yet)
  • The cable ends may have issues (there again, the repeater can transmit well if I am standing next to it and someone else is at a distance talking to me on a cell phone, they can hear but when they transmit back nothing comes in.)
  • The duplexer built into this little repeater may be faulty
  • The duplexer may be off tune (I don't yet have the tools to tune it)
  • The final issues is, I may have purchased the wrong repeater!    Don't laugh at me, this was my first repeater and I was trying to go cheap.  I am learning the cheap often cost more in time and effort and money! 
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SO your going to need some basic test equipment to determine your issue. First is a DVM and second is a basic watt meter. First thing I'd do is take a DVM and check the antenna line and make sure the center and shield are not shorted. You did not mention cable type, length or antenna specification so can't help alot without that info. A watt meter would allow you to test output power of the repeater as well as antenna system. The RT97 is a great little repeater for home use and with the proper accessories can be a great little box. Who did programming and tuning on duplexer ? Did you specify the repeater frequency to them when ordering ? 

 

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gortex2,

Thank you. I just now took my Digital Multimeter and tested for continuity, it's not shorted. I also tried testing ohms but not sure what I'm doing it just read LOW on every ohms scale. 

Also I took a picture of the cable.  The antenna is an 8db omni antenna (about 7' long white one 3 pcs screwed together  with also 3 prongs at the base, seems like a good quality antenna)

What testing equipment do I need?

20220417_104651.jpg

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If that's RG58 that could be your culprit; suggest rolling up to at least good quality LMR400 to get it to work OK. By the book you should be running hardline, but that's overkill for this application IMO. Cheap coax makes noise under power of which a primary symptom is heavy receiver desense.

Also if you purchased an RT97 for the wrong band the notches on the internal duplexer will be way out of wack; meaning your receive is basically not protected from the repeater's transmitter at all (again, you'd get some major desense here). You can 'kinda' tune them with a nanoVNA (not well I should add, but you can get in the ballpark), but if you're not familiar with the process I'd have either a local comms shop do it for you or exchange it with Retevis.

Edited by JeepCrawler98
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Hardline is LDF4-50A. Its a very stiff cable and is not great for bending. Thats the benefits of loss. If your under 50' grab some LMR400. Anything more that 10-15' of RG58 and you wont have any signal on the antenna port. Who tuned the antenna and set it up on frequency ? It sounds like you ordered a TRAM style put together antenna and they need cut to specific lengths to work properly. As said above this was ordered and programmed for GMRS ? 

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gortex2,

Ok, I ordered some LMR400 (yes we are about 25'-35' long cable).

Generally how do you tune those white fiberglass antennas?  Do I need to get me an SWR meter?

Here is what the antenna looks like: https://www.amazon.com/HYS-Dual-Band-Heavy-Duty-Fiberglass-UHF-Female/dp/B0956XKGC5

The duplexer inside the repeater is a: Jiesai duplexer sgq-450x with SMA connectors (10-20W small little thing)   I have a nephew coming to check out the duplexer tuning with his fancy tools next weekend.

I have enough knowledge to program the frequencies and tones and bandwidth settings, etc.   I think it's cable and antenna issues.

Hey, do connector types make a difference   type N vs PL-259 ?

By the time I'm done I may have a different antenna, different cable, and a different repeater! 😉  That's part of the tuition of learning.

Thank you so much for your help.

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PL-259 has decent loss at UHF frequencies; Type N is much better to use and is all you'll find on commercial repeater setups (sometimes even DIN 7/16 or flange connectors). On end-user equipment manufacturers tend to stick to the PL-259's since it's what people are more used to working with and they're robust.

You should get an SWR meter to check that antenna, it also looks like it has a few exposed joints in it; joints can raise the noise floor under power as well so it's yet another thing to watch out for. If you do end up switching it out for another model go for one with Type N connectors and crimp on a fitting on that LMR400. The Diamond X50C2 works decent for a home-use repeater and has some gain for the price, if you go above that start looking at used DB404/408/411's

Be mindful that when it comes to full duplex repeater setups; all the small unexciting details become a lot more important than the repeater itself - filtering, feedline and antennas are everything.

Edited by JeepCrawler98
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I have two of these units. The both worked fine out of the box. 

First thing I would check is that you are not testing it by trying to talk between two radios in close proximity to each other. When you do this the radios overpower the repeater. If you attempted to test this way move the radios further apart and try it again.

With that out of the way you have a few other things being talked about.

Make sure your antenna on the RT97 is at least close to being tuned for GMRS. If it was marketed as such when bought it should be good enough to work. Further tuning would just tweak the performance a bit better.

The next would be coax leading to the antenna. The RT97 is a low power machine, 5-10 watts. You can lose that real fast with low quality coax. LMR400 would be a much better upgrade to RG58. You, in theory, may run into noise issues with LMR400. Long story short and vastly over simplified, as a radio tranmitts it puts power into the coax, the dissimilar materials in the LMR400s shielding can cause "sparks and arcs". Those "sparks and arcs" make RF noise. Those normally don't cause issues on a regular radio because it is not receiving at the same time. A repeater is receiving at the same time it is transmitting and those noise gets repeated.  If you want to run coax look for something like RG393. It's all silver plated and doesn't suffer this issue. If you want to do it "right" get hardline. I run RG400 on my RT97s as I only run about 6 feet to the Antenna from the RT97. RG400 is thinner RG393.  But this is all theory and I have heard people use LMR400 without issue.

 

The UHF connector, while not ideal in theory, made zero functional difference when I swapped it out to a type N. Granted the biggest advantage the type N affords me is it's weather resistance which is better.

 

 

Your RT97 is weather resistant and uses very little power. You can leverage this by mounting the RT97 to the tower and powering it by solar. This keeps your coax run short and keeps that RT97 running for "free" and off grid if the power fails.

 

I don't know where you are and how much you time want to spend transmitting but a simple 30 watt panel, small solar controller and 12 volt battery can be plenty.

 

 

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I think what I am going to do is pull this down off the tower and set it up in my camp trailer with a short cord.   Then I am going to buy a different antenna, cable, and a bigger repeater for the tower location.   Thank you to all for your input.  I am learning a lot.

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On any repeater you can use one --and-- only one frequency pair, and the duplexer should be tuned to the chosen frequency pair.  I have never figured out why they chose to have 16 memory slots!

You never did say whether you told Retivis what frequency pair you wanted.  They tune the duplexer before sending the unit.

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The notches on most duplexers are about 200-300Khz wide if not wider for the +/- 3dB measurement from peak loss (ie. if your max is -88db, the range from where you'd have -85 to -88 to -85). So within GMRS, you're absolutely frequency agile with your repeater. It's a misnomer that your duplexer is only good for one pair given how small the band is, on other services though you may not be so lucky.

On the full Pass/Reject duplexers the pass band is usually about a Mhz wide, unless you add additional pass cavities (always a good idea).

Duplexers aren't as pointy as people think; so long as Retevis aimed for somewhere in the GMRS band and hooked the leads up correctly it should be usable.

Edited by JeepCrawler98
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13 hours ago, WRFP399 said:

I have used my RT97s on all of the GMRS freq pairs and while the testing was not extensive I found them to work on all pairs between 550-725.

Define "work." I've owned an RT97 for over a year by now. Yes, the repeater will work on all 8 frequency pairs, but only the one the duplexer is tuned for will work efficiently. As you move up or down from that tuned pair, the reception will get weaker and weaker, and the transmitter's ERP will likewise diminish.

When I deploy the repeater in the field with the antenna up on 40' telescoping mast, on the tuned pair the average range from the antenna is around 8 miles. When tuned to either end from the tuned pair, average distance from the antenna drops to around 600'. YMMV of course.

 

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14 hours ago, JeepCrawler98 said:

Duplexers aren't as pointy as people think; so long as Retevis aimed for somewhere in the GMRS band and hooked the leads up correctly it should be usable.

I am speaking about maximum ERP, reception range and efficiency based on my own testing. 

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On 4/20/2022 at 10:59 AM, n4gix said:

Define "work." I've owned an RT97 for over a year by now. Yes, the repeater will work on all 8 frequency pairs, but only the one the duplexer is tuned for will work efficiently. As you move up or down from that tuned pair, the reception will get weaker and weaker, and the transmitter's ERP will likewise diminish.

When I deploy the repeater in the field with the antenna up on 40' telescoping mast, on the tuned pair the average range from the antenna is around 8 miles. When tuned to either end from the tuned pair, average distance from the antenna drops to around 600'. YMMV of course.

 

The RT97 tuned at 550 RX/TXing on 625 out to around 20 miles to using a dual-band GMRS/MURS roll up hastily thrown in a tree while my 625 repeater was down due to lack of solar.

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We are still twinking with this little repeater, and learning.   So my SWR meter arrived and I connected it between the repeater and antenna.  This is what I got. (see picture)   Not sure what it means, other than the 1.02 seems right.   The question is the 0.698w is that the incoming power?  Is this because my coax is small?   (My LMR-400 is still coming.)  What else can I learn from this?

20220423_103627.jpg

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In your case the 0.698 w is the power going forward, from the transmitter towards the antenna. You see it also in the FW value at the bottom left of the screen. 
RW shows the Reflected power, which you want to minimize. On yours that’s shown as 0.000w which makes sense given your low SWR

If you had a high SWR your reflected power would also be high. 

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Your output power is much lower than it should be; my understanding is that the RT97 has a 10w PA, but since you have fairly high losses when you put those Jesai duplexers at a 5mhz split they rate them to 5w out (they advertise the amateur one at 10watts… with a 10mhz split)

if you’re seeing 700mw forward, and if that Surecom is halfway accurate (they’re usually at least in the ballpark) I’m wondering if your duplexer is poorly tuned, hooked up backwards, or otherwise defective. It’d be worth putting that meter between the low port and transmitter port in the repeater and seeing what your output is there. Is there a high/low power setting in the software that might be messing with things?

Edited by JeepCrawler98
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Your output power is much lower than it should be; my understanding is that the RT97 has a 10w PA, but since you have fairly high losses when you put those Jesai duplexers at a 5mhz split they rate them to 5w out (they advertise the amateur one at 10watts… with a 10mhz split)
if you’re seeing 700mw forward, and if that Surecom is halfway accurate (they’re usually at least in the ballpark) I’m wondering if your duplexer is poorly tuned, hooked up backwards, or otherwise defective. It’d be worth putting that meter between the low port and transmitter port in the repeater and seeing what your output is there. Is there a high/low power setting in the software that might be messing with things?
Or a blown final and the driver is providing the output.

Sent from my SM-A125U using Tapatalk

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@JeepCrawler98, I finally got my connector to connect from N to SMA so I can test the radio transmit without the duplex. See attached image.  This is the power output without the duplexer, as compared to the picture from a few post back that had the duplexer.   I didn't see any power setting switch in the software.    I was having trouble receiving a signal,,, and this is showing really low power output as well.  Oh, and by the way, it's not the coax nor antenna because I still have that same smaller coax connected to a 40W repeater (Vertex EVX-R70) and it works nicely.   So it is something to do with this little Retevis RT97.

20220427_164351.jpg

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That’s definitely low and the manual doesn’t mention a low power setting but does say you need a power supply of 12-24 volts. What does the incoming power supply voltage look like when you’re transmitting?  Is it sagging?

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