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Poor Performance of new Repeater...


n4gix
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I have been having some poor receive sensitivity with my new Bridgecom repeater system, and I'm trying to narrow down just where I might take some action to improve things. Beginning with the antenna system seems a good place to start.

 

The antenna is a monoband Comet CA-712EFC mounted on a roof tripod on a 10' mast. With the combined height of the roof the base of the 8' antenna is at 52' AGL. The feedline is 60' of new 1/2" Comscope heliax, which terminates in a new MFJ-270 Lightning Surge Protector (Gas) just outside my office/shack exterior wall. It is brought into the repeater with 6' of RG-213.

 

I've done a sweep of the entire antenna system with a Surecom SA-250 Antenna Analyzer. The lowest SWR is 1.09 @ 461.275 MHz. At the receive frequency of 467.675 MHz the SWR is 1.32 (see details in next image) :

http://puu.sh/or8Lw.jpg

 

Averages on a single frequency, 10 pass sweep are shown in the next image. The camera didn't focus too well for this image, but it should still be readable.

SWR 1.32

Zx 50.1 ohms

Rs 57.5

jX -28

 

http://puu.sh/or9sa.jpg

 

The final image is at the transmit frequency of 462.675 MHz. This image is crystal clear so I won't transcribe the results. I cannot spot anything that stands out as a possible problem.

 

http://puu.sh/or9Kn.jpg

 

The last image is a composite trace of the duplexer. Note that the insertion loss at the receive frequency is -1.42 dB, which isn't all that bad! The reject of the transmit frequency isn't all that spectacular, but should be acceptable at -70.81 dB.

 

http://puu.sh/ora4W.png

 

The transmitter is limited to 20 watts output in an attempt to better balance the system. It is capable of a full 50 watts continuous duty.

 

Range testing with a 4 watt Motorola XPR7550 shows full quieting at 1 mile, 70% quieting at 2 miles, but unreadable at 3 miles. With the antenna height and average 5' portable/mobile height, I should be seeing around 10 miles for 70% HT coverage by my calculations.

 

Does anyone have any suggestions as to where next to look?

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I think you may be expecting to much for 52' AGL. My GMRS Tower is 150' AGL and 232' AAT Running 7/8 Cable, 4 cavity EMR Duplexer and a DB420 antenna at a full 50W.  I also use the XPR7550 and have tested full quieting to 12 miles and usable at ground level to 20. Mobile coverage with a 1/4 wave is a solid 35 miles radius around the tower.

 

My main part 90 UHF site has the RX antenna at 460' with my TX at 150'. I get HT coverage into 3 surrounding counties.

 

You never said what your mobile coverage is or what your HAAT is. At 52' terrain has a huge impact, you could be dropping 15' in elevation 2 miles away and 20' in 3. If you have a GPS with elevation drive around and see what the land is doing.

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Latitude 41.62674593

Longitude -87.51556871

 

The terrain around me is relatively flat for at least a 20 mile radius.

 

FWIW, I had a long QSO with a friend who's currently at work. His 4watt HT connected to a roof mounted mag mount 1/4 wave was about 40% quieting with a lot of 'hash' in his audio.

 

During the QSO I switched to 'base mode' on the repeater and his signal improved to at least 95% full quieting with only a soft "hiss" on the audio.

 

This begins to smell like a de-sense issue with the duplexer.

 

From the https://www.fcc.gov/media/radio/haat-calculator

My average HAAT is 20.3m, or 66.6'

|41|37|36.28|N|87|30|56.05|W|NAD 27|
|202.0  meters RCAMSL|
|20.3   meters Calculated HAAT|
|NGDC/FCC Continental USA|
|  0.0|    22.0|
|  1.0|    22.0|
|  2.0|    22.0|
|  3.0|    22.0|
|  4.0|    22.0|
|  5.0|    22.0|
|  6.0|    22.0|
|  7.0|    22.0|
|  8.0|    22.0|
|  9.0|    22.0|
| 10.0|    22.0|
| 11.0|    22.0|
| 12.0|    22.0|
| 13.0|    22.0|
| 14.0|    22.0|
| 15.0|    22.0|
| 16.0|    22.0|
| 17.0|    22.0|
| 18.0|    22.0|
| 19.0|    22.0|
| 20.0|    22.0|
| 21.0|    22.0|
| 22.0|    22.0|
| 23.0|    22.0|
| 24.0|    22.0|
| 25.0|    22.0|
| 26.0|    22.0|
| 27.0|    22.0|
| 28.0|    22.0|
| 29.0|    22.0|
| 30.0|    22.0|
| 31.0|    22.0|
| 32.0|    22.0|
| 33.0|    22.0|
| 34.0|    22.0|
| 35.0|    22.0|
| 36.0|    22.0|
| 37.0|    22.0|
| 38.0|    22.0|
| 39.0|    22.0|
| 40.0|    22.0|
| 41.0|    22.0|
| 42.0|    22.0|
| 43.0|    22.0|
| 44.0|    22.0|
| 45.0|    22.0|
| 46.0|    22.0|
| 47.0|    22.0|
| 48.0|    22.0|
| 49.0|    22.0|
| 50.0|    22.0|
| 51.0|    22.0|
| 52.0|    22.0|
| 53.0|    22.0|
| 54.0|    22.0|
| 55.0|    22.0|
| 56.0|    22.0|
| 57.0|    22.0|
| 58.0|    22.0|
| 59.0|    22.0|
| 60.0|    22.0|
| 61.0|    22.0|
| 62.0|    22.0|
| 63.0|    22.0|
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| 65.0|    22.0|
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| 69.0|    22.0|
| 70.0|    22.0|
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| 72.0|    22.0|
| 73.0|    22.0|
| 74.0|    22.0|
| 75.0|    22.0|
| 76.0|    22.0|
| 77.0|    22.0|
| 78.0|    22.0|
| 79.0|    22.0|
| 80.0|    22.0|
| 81.0|    22.0|
| 82.0|    22.0|
| 83.0|    22.0|
| 84.0|    22.0|
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| 86.0|    22.0|
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| 96.0|    22.0|
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| 99.0|    22.0|
|100.0|    22.0|
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|102.0|    22.0|
|103.0|    22.0|
|104.0|    22.0|
|105.0|    22.0|
|106.0|    22.0|
|107.0|    22.0|
|108.0|    22.0|
|109.0|    22.0|
|110.0|    22.0|
|111.0|    22.0|
|112.0|    22.0|
|113.0|    22.0|
|114.0|    22.0|
|115.0|    22.0|
|116.0|    22.0|
|117.0|    22.0|
|118.0|    22.0|
|119.0|    22.0|
|120.0|    22.0|
|121.0|    22.0|
|122.0|    22.0|
|123.0|    21.9|
|124.0|    21.8|
|125.0|    21.6|
|126.0|    21.3|
|127.0|    21.0|
|128.0|    20.7|
|129.0|    20.5|
|130.0|    20.3|
|131.0|    20.2|
|132.0|    20.2|
|133.0|    20.3|
|134.0|    20.1|
|135.0|    19.8|
|136.0|    19.4|
|137.0|    19.1|
|138.0|    18.9|
|139.0|    18.9|
|140.0|    19.0|
|141.0|    19.2|
|142.0|    19.4|
|143.0|    19.6|
|144.0|    19.6|
|145.0|    19.3|
|146.0|    19.0|
|147.0|    19.0|
|148.0|    19.1|
|149.0|    19.0|
|150.0|    18.6|
|151.0|    18.0|
|152.0|    17.5|
|153.0|    17.2|
|154.0|    16.9|
|155.0|    16.8|
|156.0|    16.9|
|157.0|    17.0|
|158.0|    17.0|
|159.0|    17.1|
|160.0|    17.3|
|161.0|    17.3|
|162.0|    17.3|
|163.0|    17.0|
|164.0|    16.6|
|165.0|    16.2|
|166.0|    15.9|
|167.0|    15.8|
|168.0|    15.8|
|169.0|    15.9|
|170.0|    16.1|
|171.0|    16.4|
|172.0|    16.7|
|173.0|    16.6|
|174.0|    16.3|
|175.0|    16.0|
|176.0|    16.2|
|177.0|    16.4|
|178.0|    16.4|
|179.0|    16.2|
|180.0|    16.0|
|181.0|    15.9|
|182.0|    15.9|
|183.0|    16.0|
|184.0|    16.0|
|185.0|    16.0|
|186.0|    16.1|
|187.0|    16.1|
|188.0|    16.0|
|189.0|    15.9|
|190.0|    16.1|
|191.0|    16.3|
|192.0|    16.5|
|193.0|    16.3|
|194.0|    16.3|
|195.0|    16.4|
|196.0|    16.7|
|197.0|    17.1|
|198.0|    17.4|
|199.0|    17.6|
|200.0|    17.6|
|201.0|    17.5|
|202.0|    17.4|
|203.0|    17.3|
|204.0|    17.0|
|205.0|    16.9|
|206.0|    16.8|
|207.0|    16.8|
|208.0|    16.9|
|209.0|    17.0|
|210.0|    17.2|
|211.0|    17.4|
|212.0|    17.6|
|213.0|    17.8|
|214.0|    18.1|
|215.0|    18.3|
|216.0|    18.5|
|217.0|    18.6|
|218.0|    18.6|
|219.0|    18.7|
|220.0|    19.0|
|221.0|    19.2|
|222.0|    19.1|
|223.0|    19.1|
|224.0|    19.2|
|225.0|    19.4|
|226.0|    19.4|
|227.0|    19.2|
|228.0|    19.0|
|229.0|    18.9|
|230.0|    18.6|
|231.0|    18.0|
|232.0|    17.3|
|233.0|    16.7|
|234.0|    16.1|
|235.0|    15.7|
|236.0|    15.4|
|237.0|    15.3|
|238.0|    15.4|
|239.0|    15.5|
|240.0|    15.5|
|241.0|    15.7|
|242.0|    16.1|
|243.0|    16.6|
|244.0|    17.2|
|245.0|    18.0|
|246.0|    18.6|
|247.0|    19.0|
|248.0|    19.0|
|249.0|    19.0|
|250.0|    19.2|
|251.0|    19.5|
|252.0|    19.8|
|253.0|    20.0|
|254.0|    20.2|
|255.0|    20.3|
|256.0|    20.6|
|257.0|    20.9|
|258.0|    21.1|
|259.0|    21.3|
|260.0|    21.4|
|261.0|    21.5|
|262.0|    21.6|
|263.0|    21.7|
|264.0|    21.8|
|265.0|    21.9|
|266.0|    22.0|
|267.0|    22.0|
|268.0|    22.0|
|269.0|    22.0|
|270.0|    22.0|
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|279.0|    22.0|
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|281.0|    22.0|
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|283.0|    22.0|
|284.0|    22.0|
|285.0|    22.0|
|286.0|    22.0|
|287.0|    22.0|
|288.0|    21.9|
|289.0|    21.7|
|290.0|    21.1|
|291.0|    20.5|
|292.0|    20.0|
|293.0|    19.8|
|294.0|    19.7|
|295.0|    19.5|
|296.0|    19.3|
|297.0|    19.0|
|298.0|    18.8|
|299.0|    18.5|
|300.0|    18.2|
|301.0|    17.9|
|302.0|    17.7|
|303.0|    17.7|
|304.0|    17.8|
|305.0|    18.1|
|306.0|    18.6|
|307.0|    19.2|
|308.0|    19.9|
|309.0|    20.4|
|310.0|    20.9|
|311.0|    21.4|
|312.0|    21.7|
|313.0|    22.0|
|314.0|    22.0|
|315.0|    22.0|
|316.0|    22.0|
|317.0|    22.0|
|318.0|    22.0|
|319.0|    22.0|
|320.0|    22.0|
|321.0|    22.0|
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|323.0|    22.0|
|324.0|    22.0|
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|326.0|    22.0|
|327.0|    22.0|
|328.0|    22.0|
|329.0|    22.0|
|330.0|    22.0|
|331.0|    22.0|
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|333.0|    22.0|
|334.0|    22.0|
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|344.0|    22.0|
|345.0|    22.0|
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|349.0|    22.0|
|350.0|    22.0|
|351.0|    22.0|
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|354.0|    22.0|
|355.0|    22.0|
|356.0|    22.0|
|357.0|    22.0|
|358.0|    22.0|
|359.0|    22.0|
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Corey, my mobile coverage is roughly 13 miles with 70% receiving the repeater, but only about 8 miles for transmitting to the repeater for 70% quieting.

 

If it doesn't rain tomorrow, I'm going to try using dual antennas and by-pass the duplexer entirely. I will use the Comet for receive, and another antenna about 10' lower and physically 42' apart from the Comet. That should be plenty of separation.

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Are you using a real duplexer or a mobile pass notch? Some other things to look at, whats the min sensitivity of your receiver? is your lighting arestor suitable for duplex use? can you get your 1/2 line right to the duplexer bypassing any jumpers, arestors etc..  I know of several system in the area that are roughly the same as you have. 3 to 5 miles HT coverage and 10 to 15 mobile is real world around here for a 50' AGL repeater.

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Mystery solved.

 

I am guessing this is close since the 8' mark 1. is at the top of your door and windows. I would almost bet the top of your door is more like 6', if that is the case subtract 2' from each increment. Using the mast to do a rough calibration of 10' I was able to use photo shop to plot some rough measurements. I think your statement  "the base of the 8' antenna is at 52' AGL" is way off. That would mean your single story ranch home has a roof peak of 42'.

 

I live in a 2 story condo with 10' ceilings downstairs,10' ceilings upstairs with 10' of attic space above it. Measuring from the peak of the roof to the ground with a tape measure I got 32'. I would guess if you re run your calculations using a 25' AGL to be realistic; you will see it is much closer to the results you are seeing in the field. It is easy to over estimate height from the ground.

 

ham.jpg

 

The below image is a 35' tower next to a typical single story house to compare.

 

ham2.jpg

 

My coverage results using 25' AGL, 6dB gain, 30W of power with an 70% reliability factor. I used 2dB of TX-RX loss to factor in the coax and duplexer. for the other end I used 6' antenna height and 2dB of gain to simulate the average car. When using 5' and 0dB of gain (HT) I got less then 3 miles. Interactive Coverage Map I have 2 commercial sites and have used this program for FCC coordination and coverage, the results have always been real close to reality as long as you input the best possible data. The difference in 25' to 35' is huge so you have to be as close as possible.

 

hamcov.jpg

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Are you using a real duplexer or a mobile pass notch? Some other things to look at, whats the min sensitivity of your receiver? is your lighting arestor suitable for duplex use? can you get your 1/2 line right to the duplexer bypassing any jumpers, arestors etc..  I know of several system in the area that are roughly the same as you have. 3 to 5 miles HT coverage and 10 to 15 mobile is real world around here for a 50' AGL repeater.

The duplexer is one that Bridgecom installed when building out my repeater. It is a Cellwave mobile duplexer with BNC connectors.

 

Ron Kochanowicz (owner/engineer) replied this morning that "...when I tested your box with a service monitor, I was getting solid decode down to less than 0.25 uV with duplexer installed." He further clarified that this was an iso-T test. Nonetheless, even he suspects a duplexer desense problem.

 

Not seen in the photos is this one showing about 10' of excess heliax. I can easily re-route the heliax through the lower sash of the window and connect it directly to the repeater to eliminate the lighting protector and the 6' RG213 jumper:

http://puu.sh/orJSo.jpg

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Mystery solved.

 

I am guessing this is close since the 8' mark 1. is at the top of your door and windows. I would almost bet the top of your door is more like 6', if that is the case subtract 2' from each increment. Using the mast to do a rough calibration of 10' I was able to use photo shop to plot some rough measurements. I think your statement  "the base of the 8' antenna is at 52' AGL" is way off. That would mean your single story ranch home has a roof peak of 42'.

Okay, you are much closer to the mark than I was. I did however step across the street to take another photo with much less parallax. I also note that I misremembered the length of the antenna. It is actually 3.2m or 10.5' high...

 

Measuring from the top of the rain gutter to the ground is precisely 11' 4". As you can see, when I stack three lines 11' 4" on top of one another, I can calculate ~34' to the tip of the antenna, which is 24' to the base, or 29' to the center point of the antenna.

http://puu.sh/orOSE.jpg

 

Obviously your range plot is much closer to reality and my own non-scientific range testing results.

 

None of this of course has anything to do with the desensing issue.

 

I posted the same info at radioreference.com and predictably several people have simply said "ditch that Comet" because it's a "hammy antenna." Er, since when was an antenna tuned for 460-470 MHz in the ham band? I'm willing to admit that it probably was a poor choice, but I can't afford a Decibel 8 bay Omni, nor would my roof tripod and mast support such a monster! smile.png

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Maybe I will have to load up the truck with my site gear and come for a visit smile.png

You would be welcome anytime! Please do let me know if you every need any help.

 

BTW, I attended a meeting of the NSEA a few weeks ago in Glenview. Among others I met Marc Drazin, who told me he should have his two repeaters back on line at the Hancock building within the next few months. He has two antennas on the roof (not in the gallery windows). No wonder his 550 machine had such terrific coverage! :)

 

He also volunteered to see if he could find me some vertical real estate here in NW Indiana.

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The duplexer is one that Bridgecom installed when building out my repeater. It is a Cellwave mobile duplexer with BNC connectors.

 

Ron Kochanowicz (owner/engineer) replied this morning that "...when I tested your box with a service monitor, I was getting solid decode down to less than 0.25 uV with duplexer installed." He further clarified that this was an iso-T test. Nonetheless, even he suspects a duplexer desense problem.

 

Not seen in the photos is this one showing about 10' of excess heliax. I can easily re-route the heliax through the lower sash of the window and connect it directly to the repeater to eliminate the lighting protector and the 6' RG213 jumper:

http://puu.sh/orJSo.jpg

 

 

I wonder if your not creating a choke with that loop...... what is that about 4 large wraps of cable?

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I am a mixed fan of BNC connectors, but I don't think that's your issue, either you bumped the duplexor, or that coil is resonating

I already checked the tuning on the duplexer with my new Rigol spectrum analyzer. See the photo in the first post.

 

I'm fixing to go out and move the heliax to pass through the window sash, and will "uncoil" the heliax at the same time. This way I can remove any "choke" that the coiled loops might be causing.

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I'm known for keeping things simple, and you guys seem to have some nice tools and put alot of thought and calculation into this. However, I will suggest 2 things from experience. 

 

1. A crappy duplexer (even if new) will mess with you all day, but look ok on instruments sometimes. (I have seen a tech put a new, expensive one even, back in the box and return it for something else after spending 8 hours jacking with it, more than once.) It happens.

 

2. I had a Ringo Ranger antenna once that was perfect in every way testing...but would not TX/RX at the same time correctly when on the repeater. And, poor receive was the issue.

 

May be nothing to do with your issues, but basically ,you can't rule anything out.  

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Maybe I can plan a ride down, your not that far away. I have all the ends, tools etc to work with that cable. In fact I think I have a few 100 feet in the garage.

That would be helpful...

 

Two updates to the situation for today. I received an email from Ron K. at Bridgecom who said that if I ship the repeater back to them in Missouri, he'll replace the duplexer with a new one from their new vendor, and also check out the entire system again, under warranty of course.

 

But first, last night I had another QSO with my friend WQVY669 from his work location near the intersection of Columbus Ave. and Indianapolis Blvd. This is about 4 airline miles from me. I could hear him faintly on the repeater, but not reliably. He said he was going to go to 462.550 simplex. On a whim I got up and wandered back into the front office/hamshack and dialed that into my TYT TH-7800 and tossed out a call.

 

Imagine my surprise when I got his reply at absolutely full quieting, with a solid four of eight bars on my digital scale! So, there are now two possibilities that occur to me since the only differences are:

 

1. antenna/feedline

2. radio receiver

 

The TH-7800 is connected to my "old" dual-band antenna at roughly the same height as my new Comet 70cm antenna. I have a new Workman dual-band antenna and coax up on a chimney mount and have now snaked that cable through the window and have it connected to the repeater (after having swept it first of course!). He'll be back at work late tonight and hopefully we can run some tests to compare the repeater's receiver with my TYT TH-7800's receiver.

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I took a drive around this afternoon and found that the repeater's performance is pretty much the same using the 10' lower Workman antenna as the 10' higher Comet and the expensive heliax.

I am strongly suspecting that it's a duplexer issue *and* a really poor front end on the receiver. Another friend kept me company and provided feedback as I drove around in roughly a 10 to 13 mile radius in my 45 watt mobile. On the 'fringes' he reported my audio was lower, but still solidly readable.

 

Tomorrow I'm going to pack up the repeater and get it ready to ship back for warranty service. I've got another "home-brew" repeater that no one seems to want to buy that I can set up while the Bridgecom goes on vacation.

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I am late to the party, but I had a similar setup as you N4GIX

 

About 40 foot to the base of the mast, tip of antenna was around 52 feet. Portables were full quiet at 1-2 miles, usable at 3-4 depending.

 

Mobile was about double that to 20 miles in places. Used a Comet 172 and 1/2 hardline on a Vertex VXR7000 pumping 38 watts (we turned it down since I run a 6 second hangtime) and saw 32+ watts out the duplexer (celwave like yours it sounds, we bench tested and desense was fine).

 

We are on top of a pretty high ridge over looking a river valley. It was sporadic on decent coverage.

 

We ended up going on a commercial tower at 220 feet, day and multiple nights difference. In speaking to a local ham over the weekend, even if I returned to my original site and went 80 to 100 feet I don't feel my issues with holes will go away.

 

I did find a tool online, don't recall where that let me plot elevation obstacles between my site and various locations. What I thought was a line of sight to different areas revealed a lot of high spots and dips that effectively created fresnels on my coverage which revealed to me that no matter what I did, I had to get height to get reliable coverage. My next debate is adding a few voting receivers to listen in the valleys were the 220 hits TX but has poor RX on portable (really just for fun)

 

Good luck, I find these new setups and improvements to be very informative.

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We ended up going on a commercial tower at 220 feet, day and multiple nights difference. In speaking to a local ham over the weekend, even if I returned to my original site and went 80 to 100 feet I don't feel my issues with holes will go away.

Thanks for the comments. Yes, height is definitely "king" and there's simply no way around that.  In retrospect, I have gone about this entire project bass-ackwards from the beginning. I should have secured a tower or building for an antenna site first, then invested in the equipment.  :huh:

 

Since it's too late now, I'll send the Bridgecom in for a doctor's visit, and continue searching for a home for it. In the meantime I'll just have to accept limited coverage. If I can get the ears to work roughly equivalent to the mouth, I'll just have to be satisfied with it for the time being.

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The BridgeCom Systems BCR-40U is on it's way back home for a hopefully successful operation and rapid recovery. It cost $50.45 to ship that 21 lbs of dead weight. <sigh>

 

The irony is that the "home-brew repeater" that I'd cobbled together which I've put on-line in the interim, works just as good as, actually perhaps a little better than the very expensive, deaf repeater!

 

I was about 8 miles from the repeater's antenna and was able to get full quieting from both my 4 watt HTs!

 

http://puu.sh/ovIft.jpg

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I got an email from Ron this morning with his findings:

Hi Bill,

Your repeater arrived a moment ago.

I have it on the bench.

 

I bumped up the TX POWER to 40 Watts into the duplexer.

 

Using my HP8920, I'm injecting to the duplexer port a 123.0 PL deviating at 500 Hz with 1 kHz tone deviating at 3 kHz on 467.675.

 

The first thing I'm seeing that seems very odd is that I'm immediately getting 40 watts out of the duplexer. 40watts in / 40 watts out. After about 30 seconds it starts to drop to 30-33 which is where it settles.

 

I should see some initial loss of around 14-17%. But, passing 40 watts and then seeing it drop seems odd. It's as if the duplexer has to 'warm' up. I've not seen this before.

 

The decode is really flaky until I take the signal strength up -116 dBm. It then stays good and solid.

 

Interestingly, I drop he signal strength to -118 dBm and then engage the repeater. The decode is really flaky as the unit puts out 40 Watts. As the power starts to drop it starts to settle in.

 

Also, from an RX side, I've bypassed the duplexer and it decodes PL very well down to -120 dBm. With the duplexer in circuit, it takes about -118 dBm to stay locked on. This is with no transmitter engaged.

 

The duplexer seems tuned okay... but it doesn't seem to be working right. You are right, when up close (or higher signal strength of -116 dBm or better) it seems to work better.

 

I welcome your thoughts... but as I suspected, it looks like this duplexer has issues. I'm not a duplexer guru, so I can't tell you what might be going on inside. I can replace it with a new one from a new mfg we started using. We're having good success so far.

 

Thank you and I look forward to your reply,

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My reply to Ron:

On 4/27/2016 2:27 PM, Bill Leaming wrote:

> On 4/27/2016 11:57 AM, Ron Kochanowicz wrote:

>> I should see some initial loss of around 14-17%. But, passing 40 watts and then seeing it drop seems odd. It's as if the duplexer has to 'warm' up. I've not seen this before.

> The material used for the tuning rods in lesser quality duplexers (mainly Chinese imports) is very frangible. They expand and contract on ambient temperature. They are usually good enough if the repeater is kept in a climate controlled environment, but can serious detune with temperature changes. RF into them can cause temperature excursions (i.e., as they 'warm up').

>> The duplexer seems tuned okay... but it doesn't seem to be working right. You are right, when up close (or higher signal strength of -116 dBm or better) it seems to work better.

>>

>> I welcome your thoughts... but as I suspected, it looks like this duplexer has issues. I'm not a duplexer guru, so I can't tell you what might be going on inside. I can replace it with a new one from a new mfg we started using. We're having good success so far.

> As part of my investigation, I did check the duplexer's tuning on my Rigol DSA 815TG spectrum analyzer. It was tuned as well as it could be, but I did note that there are some unusual 'dips' that shouldn't be present. I put a Marker on 467.675 and noted -1.41 dB insertion loss, which is acceptable I believe. I was however concerned that the notch depth at 467.675 is only -65.3 dB.

>

> I mention another duplexer that I have had some very mixed results with on an "home-brew repeater" that I built. On this duplexer, the first can on the receive side had to be "de-tuned" slightly in order to allow any RF to pass at all. It is incapable of 5 MHz bandwidth! Insertion loss on the transmit frequency was -5.24 dB. Once that one can was de-tuned down to nearly 7 MHz, I was able to get the insertion loss down to -0.85 dB and finally the transmitter could pass RF. The day I shipped the unit back to you I was able to hit this repeater at 8 miles with both my 4 watt HTs (MD-380 and XPR7550) with 80% full quieting using my Comet antenna and heliax. That was with only 12 watts at the antenna port of the duplexer.

>

> Let's replace the duplexer then and see how it goes. If you don't see anything funky with its performance, then we'll see how it performs here when it's returned. I'm not expecting miracles given the constraints of my current antenna system, but if it can receive as well as it transmits, and perform at least as well as my "home-brew" repeater, I'll be satisfied.

>

> Meanwhile, the search for a better location and height continues! ;)

Incidentally, I received a reply just now that a new duplexer has been ordered, and should arrive in about three days. Then he'll tune it up, install it, and test thoroughly before returning it to me. <fingers-crossed-mode:ON> :)

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