Duplexer Problem? Motorola GMRS Repeater

[rescue161]

As Kayn pointed out, the quality control on the tuning rods leaves a lot to be desired. While tuning, the waveform on the monitor will jump quite a bit. Mine was so bad that it was just unusable for my application. Mine was just to add isolation between two repeaters (GMRS/ham - each with their own BPBR duplexers), but the insertion loss was just too great.

 

[rescue161]

I was considering this Motorola MSF5000 100 watt UHF duplexer.
I found someone to tune it as well for a fee.

Go with a Celwave 526. You'll have MUCH better performance than with that MSF5000 unit.

 

[kayn1n32008]

As Kayn pointed out, the quality control on the tuning rods leaves a lot to be desired. While tuning, the waveform on the monitor will jump quite a bit. Mine was so bad that it was just unusable for my application. Mine was just to add isolation between two repeaters (GMRS/ham - each with their own BPBR duplexers), but the insertion loss was just too great.

Yea, the screw, with locking nut is a PITA to tune... Well not tune, but to maintain once tuned as you tighten down the locking nut... Oh the nightmares....


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[kayn1n32008]

When I ordered the duplexer, I gave them specific TX and RX that I am using. They even wrote the frequency on the high and low ports. I never touched any of the tuning screws. I can tell the screws were adjusted because of the paint marks but there is a nut to keep them locked into place. I was very leery of going the Asian route "no offense intended" but was reassured by some reviews that the most notable problem with them was that they may cause slight interference with a close frequency.

A friend and I compared an ebay China special duplexer to an actual Sinclair mobile duplexer, and surprisingly they were just as good, at least the one we compared was.

I don't have any equipment to test the duplexer but at this point, I think I am going to start by replacing it first. I also contacted the seller of the duplexer to let them know the amount of wattage loss. If its only supposed to be 1 db, I still think it has a problem or was falsely advertised.

I doubt it is false advertising, but likely it was jarred during shipping, or something like that. The guy that tuned it may have just not cares enough to get it perfect too.

I was considering this Motorola MSF5000 100 watt UHF duplexer.

I found someone to tune it as well for a fee.

Please LISTEN to what we are suggesting to you.. First things first, dump the LMR cable. Then find someone that can verify the tuning of the duplexer. Do not start throwing good money after bad by buying inferior equipment and expecting it to fix your problems. Inferior equipment will give you inferior results.

Do not waste your money on the MSF duplexer, go and find a Celwave or Sinclair that is a proper BpBr duplexer.




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[petnrdx]

That is not a duplexer.
It is a pre-filter and post filter for an MSF5000 transmitter.
Won't work for you.
That "pre-post filter" arrangement works in the MSF with a particular length coax Tee arrangement, AND the extremely large, very selective receiver front end of the MSF.
So, what you are looking at is really only "half" of the duplexing setup of the MSF5000.
It is a kind of unusual setup.
The small filter on the left end is a filter that goes between the exciter and the PA
The larger section on the right is to filter after the PA, then goes the "critical" length coax TEE section that spilts the antenna feed to the RX.
Look for a real duplexer.

 

[linboogy]

Ok, I dumped the idea of the Motorola cavity
I'm going to start with coax
I have read some suggestion on heliax. I'm on a budget of course so any suggestions on how low I can go on the coax?
Thanks again

 

[rescue161]

Commscope LDF4-50A (1/2" Heliax) is available for $1.99 a foot from www.theantennafarm.com

You can usually pick up the same on Ebay for about $1 a foot, but the auctions end fast. I would not go under 3/8" Heliax. There is a nice loss calculator here: Coax Loss Calculator where you can see the pros/cons of each feedline.

 

[linboogy]

Commscope LDF4-50A (1/2" Heliax) is available for $1.99 a foot from The Antenna Farm, Your two way radio source

You can usually pick up the same on Ebay for about $1 a foot, but the auctions end fast. I would not go under 3/8" Heliax. There is a nice loss calculator here: Coax Loss Calculator where you can see the pros/cons of each feedline.

Wow
I didn't realize how important coax is. That's a really nice calculator

 

[prcguy]

Where are you located?
prcguy

Wow
I didn't realize how important coax is. That's a really nice calculator

 

[linboogy]

Where are you located?
prcguy

Cincinnati Fleming Rd 45231

 

[prcguy]

Ok, too far away to send u some free Heliax. If you have any amateur radio swap meets in your area you will find some cheap.
prcguy

Cincinnati Fleming Rd 45231

 

[linboogy]

Any input on this Andrew Heliax cables, 3/8 inch X 50 feet. 50 ohm, low loss foam dielectric
FSJ2-50

 

[rescue161]

It is okay, but connectors are much easier to find for the 1/2" stuff. Plus, it's higher loss. It isn't even listed on that coax calculator that I sent.

 

[linboogy]

It is okay, but connectors are much easier to find for the 1/2" stuff. Plus, it's higher loss. It isn't even listed on that coax calculator that I sent.

It already has the N connectors on it. I don't want to waste the time and money on it though if its going to put me in the same boat but if its justifiably better than the 400 coax I am wanting to pull the trigger on it

 

[rescue161]

I would still try to stick with 1/2", but yes, the 3/8" is still better than LMR400 for repeater service.

 

[linboogy]

I found a small communications shop called Meyer Electronics here in Cincinnati while trying to find some Heliax. He pretty much told me it was going to be expensive but when I told him I needed 50 feet, he was questioning what I needed it for so I told him about the repeater. He was telling me he sets up repeaters here locally "I only taking this with a grain of salt" but he said the LMR 400 should be fine in this situation with only 50 feet but he rather seemed interested in testing everything out. I did not know that he offered this service. So from this point he said bring the whole repeater in and he will start with a 1 hour bench check to test the duplexer and "desensitization". It 70$ per hour but I think from all the info you guys have gave me so far, this is the best route to go.
Does that seem unreasonable?

 

[jsikora]

In reality what you are seeing is about correct for the antenna and cable you have. I have multiple GR1225 repeaters all set for 25 watts TX (45 watt PA turned down) and routinely see between 15-18 watts out of the duplexer at the rear of the chassis. Couple that with LMR400 (junk for duplex) and its not going to work too well. I run a DB404 on all my GR1225 Repeaters with 30-50 feet of 1/2" Andrews Hard Line. I also have checked all the cheap duplexers on my service monitor and you will see 1.5 to 3 db of loss thru them. Changing out the jumpers between the radio to the duplexer will help very minimal. It will help but not resolve your issue. Get a real antenna and real hardline.

BTW - I run the same mobile duplexer (1 is NOS from Motorola and 2 are China Ebays Units) and on 2 repeaters have all 5 pairs in it however have it tuned to the center frequency.

 

[linboogy]

In reality what you are seeing is about correct for the antenna and cable you have. I have multiple GR1225 repeaters all set for 25 watts TX (45 watt PA turned down) and routinely see between 15-18 watts out of the duplexer at the rear of the chassis. Couple that with LMR400 (junk for duplex) and its not going to work too well. I run a DB404 on all my GR1225 Repeaters with 30-50 feet of 1/2" Andrews Hard Line. I also have checked all the cheap duplexers on my service monitor and you will see 1.5 to 3 db of loss thru them. Changing out the jumpers between the radio to the duplexer will help very minimal. It will help but not resolve your issue. Get a real antenna and real hardline.

BTW - I run the same mobile duplexer (1 is NOS from Motorola and 2 are China Ebays Units) and on 2 repeaters have all 5 pairs in it however have it tuned to the center frequency.

I think right now I am going to go with the Andrew 3/8 FSJ2-50
I figured my Antenna was OK, What are you recommending?

 

[linboogy]

Never mind, I see that you listed a model number on the antenna

 

[linboogy]

Just wanted to update
Installed the Andrew 3/8's Heliax and replaced the Antenna with a Comet CA-712EFC 9DB gain antenna
The SWR is 1.1
The power for some reason went from 15 watts to 20 watts on my meter. The N connectors were pre installed on the Heliax
I am still having the same exact issue. Very spotty coverage and not hardly able to hit an HT 3 miles away
Other than taking the repeater to get it serviced, I am out of things to try.
Any other ideas? could it just be desensitized from this point?