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#1 CogentRadios

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Posted 28 March 2021 - 04:32 PM

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?


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#2 WRAK968

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Posted 28 March 2021 - 05:10 PM

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.


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#3 WRAK968

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Posted 28 March 2021 - 05:13 PM

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.



#4 JohnE

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Posted 28 March 2021 - 05:36 PM

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.


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#5 WRKC935

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Posted 28 March 2021 - 07:10 PM

. 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?



#6 axorlov

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Posted 29 March 2021 - 12:36 AM

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.


- Alex


#7 WRAK968

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Posted 29 March 2021 - 05:21 AM

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.



#8 CogentRadios

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Posted 29 March 2021 - 06:48 AM

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.

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#9 kb2ztx

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Posted 29 March 2021 - 11:12 AM

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.



#10 CogentRadios

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Posted 29 March 2021 - 11:22 AM

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 


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#11 Radioguy7268

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Posted 29 March 2021 - 02:46 PM

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".



#12 CogentRadios

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Posted 29 March 2021 - 03:24 PM

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.

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#13 JohnE

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Posted 29 March 2021 - 04:45 PM

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


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#14 CogentRadios

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Posted 29 March 2021 - 07:34 PM

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'.

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#15 JohnE

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Posted 29 March 2021 - 07:59 PM

 

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

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


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#16 CogentRadios

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Posted 29 March 2021 - 08:03 PM

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.

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