Very frustrated...

[CogentRadios]

Completed the 50' Rhon45 tower install yesterday, mounted a tram 1450 uhf antenna on the top and fed it with 1/2" EDC4-50 hardline. I used a Comet mkII caa analyzer at the end going into the vxr7000 and it shows 49 ohm and 1.1 swr output is 50watts.

So everything seems near perfect, I am on a high point but I can only get into the repeater from about 1/4 mile away. The only thing I think can be an issue is the Tram 1450 antenna, it is just a wonderful dummyload. I ordered a DB408-b and a 22' chrome molly mast as a replacement. I was hoping to get at least 2 miles out of this current system. Anyone have any suggestions?

[WRAK968]

If you are using this in repeater mode you need a tuned duplexer for the repeater pair you are using. DO NOT TRUST CHINA'S DUPLEXERS as they seem to fail time and time again, not to mention they are never tuned properly from the factory. I would say this is likely where your issue lies.

[WRAK968]

Also, most flat packs, while rated at 50W output, are typically meant to be operated at about 25W. Reduce power and test your range.

Personally I prefer BPBR duplexers. if you research enough you can get one for about $300. You may still be limited to low-mid power depending on the specifications, however you will see your range drastically increased.

[JohnE]

I'm going to say duplexer also, maybe the cables are backwards. Have seen that a couple of times. A celwave flat pack is deigned to fit inside that machine and has the provided jumpers. I have 2 of them as spares.

[WRKC935]

. You may still be limited to low-mid power depending on the specifications, however you will see your range drastically increased.

This statement is based on what exactly?  I run two systems that are on DB420's for TX and RX.  One has an 8 port combiner and the other has a 6 port combiner.  Cable for TX and RX is 7/8.  Cable length is 400 on one and over 500 on the other.  Combiner loss is 4-6 db depending on the port and the base stations are set for 20 watts.  The system consistently out talks it receive but has a 50 mile radius of operational use.  Height is of WAY more importance than power out.  If you sit down and run the numbers, 20 watts out of the repeater into a 6 db loss is 5 watts up the cable.  500 feet of 7/8 cable is .787 per 100 foot.  That is an additional 4 db of loss and two connectors are an additional .5 each.... total cable loss is 5db. So 5 watts into 5 db of loss gives you 1.58 watts at the antenna connector.  Antenna gain is 11.3 db.  That makes the ERP 20 watts.  And it talks over 50 miles in all directions.  Of course the reason it don't hear as well is there is no tower top amplifier driving the receive cable and the loss ends up being too great for TX/RX  equalization.  The Tram antenna is 5 dbi gain.  Not the best thing on the planet but it's better than a coat hanger.    The tower is 50 feet so the cable run is under 100 foot.    Yes, his duplexer is showing an issue, but the cables being backwards aint it depending on where he checked the Power out.  If backwards, the output would have been no where close to 50 watts same as if it were mistuned on the TX side.  RX tuning may be an issue, as well as a bad RX cable. 

 

Point is that the loss of 3 or even 6 db of power level has only a small effect on the overall range of a repeater, depending on the circumstance of the installation.  

Here's a better question... Where did he check the SWR and what meter did he use?  Reason for this question is simple.  Go back to my install.  Take a Bird meter and check the forward and reflect at the combiner output. 

You use a 25 watt slug, forward is 5 watts, reflect is .5 watts... why is even doing this wrong, and what is the actual reflected power at the antenna?

[axorlov]

Completed the 50' Rhon45 tower install yesterday, mounted a tram 1450 uhf antenna on the top and fed it with 1/2" EDC4-50 hardline. I used a Comet mkII caa analyzer at the end going into the vxr7000 and it shows 49 ohm and 1.1 swr output is 50watts.

 

So everything seems near perfect, I am on a high point but I can only get into the repeater from about 1/4 mile away. The only thing I think can be an issue is the Tram 1450 antenna, it is just a wonderful dummyload. I ordered a DB408-b and a 22' chrome molly mast as a replacement. I was hoping to get at least 2 miles out of this current system. Anyone have any suggestions?

Make a plan for troubleshooting. It seems that you suspect an antenna, for whatever reason. So, confirm or refute this hypothesis, that the antenna is the trouble. Send a buddy in the car 15 miles away and communicate with him through this antenna and feedline on simplex, bypassing all the wonderful machinery, diplexers and stuff. Make sure you trust the antenna and the feeder. With the result on hand, the next troubleshooting step will become apparent.

[WRAK968]

This statement is based on what exactly?  I run two systems that are on DB420's for TX and RX.  One has an 8 port combiner and the other has a 6 port combiner.  Cable for TX and RX is 7/8.  Cable length is 400 on one and over 500 on the other.  Combiner loss is 4-6 db depending on the port and the base stations are set for 20 watts.  The system consistently out talks it receive but has a 50 mile radius of operational use.  Height is of WAY more importance than power out.  If you sit down and run the numbers, 20 watts out of the repeater into a 6 db loss is 5 watts up the cable.  500 feet of 7/8 cable is .787 per 100 foot.  That is an additional 4 db of loss and two connectors are an additional .5 each.... total cable loss is 5db. So 5 watts into 5 db of loss gives you 1.58 watts at the antenna connector.  Antenna gain is 11.3 db.  That makes the ERP 20 watts.  And it talks over 50 miles in all directions.  Of course the reason it don't hear as well is there is no tower top amplifier driving the receive cable and the loss ends up being too great for TX/RX  equalization.  The Tram antenna is 5 dbi gain.  Not the best thing on the planet but it's better than a coat hanger.    The tower is 50 feet so the cable run is under 100 foot.    Yes, his duplexer is showing an issue, but the cables being backwards aint it depending on where he checked the Power out.  If backwards, the output would have been no where close to 50 watts same as if it were mistuned on the TX side.  RX tuning may be an issue, as well as a bad RX cable. 

 

Point is that the loss of 3 or even 6 db of power level has only a small effect on the overall range of a repeater, depending on the circumstance of the installation.  

Here's a better question... Where did he check the SWR and what meter did he use?  Reason for this question is simple.  Go back to my install.  Take a Bird meter and check the forward and reflect at the combiner output. 

You use a 25 watt slug, forward is 5 watts, reflect is .5 watts... why is even doing this wrong, and what is the actual reflected power at the antenna?

Personal experience. Using a celwave flat pack that was tuned by a professional shop (ARCOMMS) gave me a range of about 3 miles. (This was on an antenna that was only 20' up with a large hill in the way) Dropping the TX power increased range by a mile or two, however the same setup with a BPBR duplexer gave me 6 miles on the other side of the hill to the north, and to the south I've had people use the repeater 10-12 miles out. When the celwave was being used they couldn't even reach the repeater.

 

As for the TX power thing, yeah, some duplexers have something called specifications which name the limits of the duplexer, and I've come across a couple that had power limits as low as 25W. I doubt the manufacture would call for a 25W limit if the duplexer could take more. Typically most duplexers are at least 200+W capable however doesn't change the fact that some aren't.

[CogentRadios]

Ok here is a followup, I have a 150 watt cellwave dup in the 7000. I have an identical setup going to a friend with the same results. So I am confident at this point it is the antenna. The Tram 1450 is obviously an awesome dummyload. Thanks for the suggestions and insight, in 30 years I have never had an antenna perform this poorly. I have a db408 on the way and excited to see the difference.

[gortex2]

Have you put a watt meter in between the repeater and antenna line ? While I think the tram is junk without real tests you can't say for sure. If your seeing this poor of performance to me there is no TX power making it to the antenna. A valid test at the back of the repeater measuring power and reflected power is needed. Additionally as others mentioned check duplexor cables and desense thru the duplexer.

[CogentRadios]

Yes everything has been tested and the antenna like I mentioned is a great dummy load. Everything is working the way it should. I think I was just surprised at how bad this antenna actually is. Like I mentioned previously I don't remember experiencing an antenna ever performing with all the correct numbers this poorly, except maybe a Firestick LOLOL. The Tram 1450 claims 5db gain and I am just wondering compared to what, a rock, I think an HT antenna would work better? LOLOL. Not sure if the beamwidth of the antenna works better at lower elevations but will let a friend try it out at his home once I get the replacement in. Either way thats what I get for not going commercial to start with. Thanks again for the responses and input.

 

Frank 

[Radioguy7268]

I've run the Tram 1486 on GMRS before with no problems. Range of 10-15 miles with a decent repeater. That's not to say every Tram 1450 is good, because I'm sure that some are junk, but it's not the design that's junk - just the tuning and the materials they're made of. Oh, and those UHF SO-239 connectors should be banned from the antenna industry. 

 

That said, have you tried out your antenna & coax just using simplex & hooking it up to a handheld or mobile? That will quickly tell you what's going on. Eliminate the repeater/duplexer/jumpers - just use an adapter straight to the coax feedline.  

 

If that doesn't work, then you KNOW it's the feedline or the antenna. If that simplex test works, then you've got some investigation to do. I'd want to sweep the line before I'd just replace the antenna.

 

A basic UHF hatpin antenna would get you 2 miles on a working repeater. Heck, I once had a hospital with a repeater antenna blown off the roof & the connector ripped out of the feedline - that was still giving them 80% of their in-building coverage. They only called because "it was a little scratchy in some spots".

[CogentRadios]

Hahahaha, a bit scratchy. I ordered a comet replacement with an N connector until I can get a boom truck and make arrangements to get the db408 in place, another week and we will see.

[JohnE]

in the mean time take 6" off the cable and put a new connector on it see what that yields.

if it works I'll explain it later

[CogentRadios]

in the mean time take 6" off the cable and put a new connector on it see what that yields.

if it works I'll explain it later

I cut the jumpers to tune, I heard anything over 30' does not matter, the hardline is 51'.

[JohnE]

 

 I heard anything over 30' does not matter, the hardline is 51'.

It can, been there done that 2x in 40 yrs. resonant cable.

[CogentRadios]

It can, been there done that 2x in 40 yrs. resonant cable.

Thanks for the insight, I am making up a new hardline and will check it on the analyzer.

[CogentRadios]

Ok, lots of progress and trouble shooting years later.

So first repeater, vx7000 worked great with Commspec 408 20+miles in south Texas flat land on 50' tower.

The same setup worked not nearly as well in Fredericksburg Va. Maybe 2.5 miles, turns out if antenna is in tree level forget it. While researching this I discovered a research project by a federal agency essentially stating that bio matter such as trees for 400 mhz and up are power sponges and pine trees are the worst.

I built several other repeaters since then using various radios such as Vertex 2100/2200, TY9000 or the Retevis models with a Id o matic repeater controller by hamgadgets.

With perfectly tuned antennas, jumpers and various name brand and Chinese type duplexers a noticeable desense issue existed in these systems making the systems virtually unuseable further than a mile out.

Fast forward to today. I invested in a real repeater, a BCR 40u from Bridgecom systems with the same antenna and duplexer as the previous radio repeaters the BCR repeater now covers spotty up to 12 miles and no more desense, with the antenna still at tree level.

So now its just a matter of getting the antenna as high as possible.

With the dual radio repeater setup everything was tried to fix the desense issue with no luck, as a last resort I thought about calling in a shaman. 

Once again while trying to fix the desense issue I found several articles relating to the sensitivity and selectivity of a repeater, these are NOT the same thing. Radios like the Vertex 2100/2200 have adjustments that can mitigate some of this but the Chinese radios do not and just dont have the selectivity to eliminate desense like an actual real repeater.

Its been a long road, but now I can expertly tune duplexers and starting to grow hair back I pulled out during this process.

I hope this helps someone and thank you to everyone that chimed in and tried to help.

Coming soon, a node to link my repeater and I look forward to hopefully talking to some of you.

 

73

Frank

 

[KAF6045]

5 hours ago, CogentRadios said:

While researching this I discovered a research project by a federal agency essentially stating that bio matter such as trees for 400 mhz and up are power sponges and pine trees are the worst.

For GMRS, I suspect 6" pine needles are a close match to a 1/4wave.

It's one reason VHF (MURS @ 2W) is suggested for use in vegetation (and 2m Amateur is probably good too, but the licensing may be a pain for some, vs no license for MURS and no-test /family/ license for GMRS).

You get a reverse condition in cities. Windows and door frames (in particular, the metal ones used on office buildings) tend to block VHF signals, while smaller UHF waves can penetrate. One reason many urban public safety systems are migrating even higher, to the 800MHz region.

 

[marcspaz]

A GMRS repeater in F'burg sounds like a great idea. There are no public access repeaters that way, that I am aware of. Of you want to get more than a couple of miles, you're going to want one. 

 

Glad to see you get yours out to 12 miles. I'm on the Manassas/Woodbridge line with mine 35' up and struggle to get about 8 miles out of it.  My land is down in a hole. I really need a 150' tower to get anything worth running full-time. 

[WRKC935]

On 3/29/2021 at 6:21 AM, WRAK968 said:

Personal experience. Using a celwave flat pack that was tuned by a professional shop (ARCOMMS) gave me a range of about 3 miles. (This was on an antenna that was only 20' up with a large hill in the way) Dropping the TX power increased range by a mile or two, however the same setup with a BPBR duplexer gave me 6 miles on the other side of the hill to the north, and to the south I've had people use the repeater 10-12 miles out. When the celwave was being used they couldn't even reach the repeater.

 

As for the TX power thing, yeah, some duplexers have something called specifications which name the limits of the duplexer, and I've come across a couple that had power limits as low as 25W. I doubt the manufacture would call for a 25W limit if the duplexer could take more. Typically most duplexers are at least 200+W capable however doesn't change the fact that some aren't.

OK, you said dropping the output power INCREASED the range?  That points to a mistuned duplexer.  Now, there is something else at play here as well.  The little Celwave notch duplexers are just that, a notch filter.  Meaning that any RF outside the notch comes in at full strength from the antenna.  And the first RF stage in a radio (including most repeaters) is not band specific.  So it can be deafened by RF from any band, not just the one of interest.  Meaning if you put a repeater on a TV or radio station transmit tower, it's not going to work very well with a notch duplexer because the high RF field will get into the radio and decrease the gain of the first stage.

A BPBR duplexer ONLY passes the frequency of interest plus a bit of RF right around the specific tuned frequency.  This means it will filter out that stray RF from a high power transmitter in the near field of the antenna.  This is also why you mount antenna's down away from broadcast transmit antenna's to get better performance form the installation. 

Duplexer power ratings

THe small notch ones are 50 watts or less.  Don't care what they say, I have tried and failed to run increased power through them.. It don't work.

Larger ones go as high as 350 watts, but are typically limited to 200 watts or less.  And most of this has to do with the maximum amount of isolation that's reasonably possible without increasing the insertion losses.   Any type of filter, the insertion losses increase with the decrease of pass bandwidth.  Very tight filters have high loss.  They are sometimes necessary for some situations, but are not worth the loss unless those specific situations are present.  Oddly enough, GMRS presents one of those specific situations.  That being transmit frequencies being very closely spaced.  Like the GMRS repeater channels.  Going from 462.550 to 462.725 in 25Khz steps, they are all close.  I personally have 3 GMRS repeaters connected to a total of 2 transmit antenna's with a common receive antenna.  This was done with a very specific setup called a HYBRID combiner.  This comblner consists of a standard UHF 4 port combiner where two or the circulators were fed directly into a 3 port power divider.  Frequencies are 462.600 and 462.675.  The can is tuned to the fequency directly in the middle between the two (462.6375).  This allows it to work, but at a cost.  With 50 watts coming from the radios, I get 18 watts out of the combiner on those frequencies.  It talks 40 miles in most directions that are not blocked by hills and valleys.  Tower height is 240 with the TX antenna at 180 but the HAAT or Height above average terrain, a calculated height based on antenna height from the ground and ground elevations for 20 miles in all directions every .5 miles divided up in 3 degree increments in the circle.  In other words.  Tower in middle of 40 circles, lines drawn out from tower every 3 degrees and everywhere there is a intersection of the lines a ground level height is taken and the number difference between the antenna height above sea level is compared.  THose numbers are all averaged out and a single number is generated.  Mine is 525 feet HAAT.  Yes, it's done with a computer and yes it takes the computer about 10 minutes to complete the calculations.  But my point is that I have 350 feet of feed line going to the antenna.  The antenna gain is 6dBi.  Using 7/8 cable so losses in the line are about 4 dB, so for all the loss it does remarkably well.

 

[Lscott]

On 4/15/2023 at 6:59 AM, CogentRadios said:

Once again while trying to fix the desense issue I found several articles relating to the sensitivity and selectivity of a repeater, these are NOT the same thing. Radios like the Vertex 2100/2200 have adjustments that can mitigate some of this but the Chinese radios do not and just dont have the selectivity to eliminate desense like an actual real repeater.

As pointed out you likely need a real band-pass/band-reject type duplexer. The cheap simple ones are just band-reject.

If your repeater is built using two radios you can add a band-pass filter inline between the RX radio and the duplexer. You can try an inexpensive one to see if that helps.

https://www.409shop.com/409shop_product.php?id=125434