repeater problem

[wqzw301]

Hello,

Repeater transmitter is a Motorola Radius. Receiver is an HT1225 board. I've had the 4 cavity band reject Duplexer professionally aligned to the programmed frequencies.

​15 watts and 1.2 on swr -with my outside mast antenna.

​Works well within about 500 yard radius.......

​ 

Using another transmitter alone on simplex, same frequency, power(15 watts) and same Antenna, I have at least 5 mile range  between base transmitter and my mobile 25 watt car transmitter. 

 

​Any thoughts on what is going on here???  The only scenario Ive come to is the old Motorola is  wide band and being used with new narrow band transmitters and receiver's. But even when I've reprogramed the newer radio's to wide band - very little improvement.

 

Reception is just as bad.

 

I have replaced all the connectors and coax.....

​Since the performance of  the Radius repeater and simplex transmitter are so different on same antenna and power output......

 

 

​If anyone has any thoughts on this problem, it will be appreciated

​Thank you,

​301

[wqzw301]

Working great now. Thanks Lads!

Celwave notch duplexer (tuned correctly) was the last piece of the puzzle....

I hit my repeater from 5 miles yesterday on a walkie - inside a bus....

Going to do some more upgrades.

I purchased a used 19" 6u rack enclosure from ebay. Going to build and isolation box for the receiver. Replace jumpers with dx engineering 400 coax double shielded and silver plated  brass connectors. Added a Sec 1235 30amp switching power supply to help run some fans...

I also added a station Id from an old surcom siplex repeater circuit connected to the RICK.

Thanks for all your help, everyone!

I learned a lot and had fun!

301 

[coryb27]

How high is the antenna? Is the antenna resonant on the freq? What type of cable, how long is the cable run to the antenna, did you hook the duplexer up backwards?

 

I am guessing TX and RX on duplexer us backwards, try swapping your cables.

 

Corey

[rdunajewski]

Also, are you comparing the repeater range by activating the repeater or are you directly keying up the repeater's transmitter to do the test?

 

If you're having any kind of receiver issue or desense issue then you're going to see that as either poor range or a fast keyup and an immediate drop of the input. Best way to make sure the TX side is good is to have someone physically key up the transmitter and verify its range independent of the repeat functionality. If that's good, start looking at the RX side for issues. If not, maybe you're slightly off-frequency and once you go out of the 500 yard range you're no longer picking up the transmitter anymore bleeding over onto the right frequency.

[WRAF213]

Also, check to make sure the coax is good. Damaged coax (eg. water ingress) can show a low SWR but still cause high losses. See if SWR stays low where you'd expect it to be higher, such as outside the antenna's resonant band.

[Radioguy7268]

Dennis - make sure that your transmit radio is going to the LOW side (462.xxx) of the duplexer. Also check your cables between the radios & the duplexer. 

 

If you're getting decent range when you eliminate the repeater from the scenario - you know your cable & antenna are most likely good. Now try doing what Rich recommends & just use a regular mobile palm mic on the transmit radio to key up the base frequency & transmit - going as a repeater normally would, through the duplexer & out through the antenna. If you start to see a problem there, you know it's something with the transmit radio (off frequency most likely) or possibly the duplexer and/or cables.

 

If the transmit radio being keyed by itself gives you the 5 mile range, but going back to a repeater function gives you problems, you can just about guarantee that it's de-sense or a terrible setup on the receive radio.

 

Using a portable 1225 "board" as the receiver doesn't sound like a sure fire path to success. The 1225 radios would easily suffer from de-sense in a heavy RF environment. I'd want to get the repeater into a shielded box & separate the receiver from the transmit radio as much as possible (A few inches and a little shielding could make all the difference).

[WRAK968]

Another thought on the subject, duplexers are rather finicky and even though they have been tuned, unless they are tested on the repeater afterwords, may still not be tuned properly. I went through this earlier this year where a new duplexer was tuned, re-tuned, and made me think it wasn't the issue. I went to my local shop with no idea why I was only able to TX @40w no more than a block when a handheld tx'ed nearly a mile. Even the radio shop tuned and tuned and found several spots where the equipment said it was tuned only to find it wasn't really tuned. After three days, they had the duplexer spot on and the repeater now tx's across town.

 

[coryb27]

Hello,

Repeater transmitter is a Motorola Radius. Receiver is an HT1225 board. I've had the 4 cavity band reject Duplexer professionally aligned to the programmed frequencies.

​15 watts and 1.2 on swr -with my outside mast antenna.

​Works well within about 500 yard radius.......

​ 

Using another transmitter alone on simplex, same frequency, power(15 watts) and same Antenna, I have at least 5 mile range  between base transmitter and my mobile 25 watt car transmitter. 

 

​Any thoughts on what is going on here???  The only scenario Ive come to is the old Motorola is  wide band and being used with new narrow band transmitters and receiver's. But even when I've reprogramed the newer radio's to wide band - very little improvement.

 

Reception is just as bad.

 

I have replaced all the connectors and coax.....

​Since the performance of  the Radius repeater and simplex transmitter are so different on same antenna and power output......

 

 

​If anyone has any thoughts on this problem, it will be appreciated

​Thank you,

​301

How can you just leave us all hanging, what was the outcome?

[wqzw301]

Sorry Guys, been a busy last week.

 

So I went through everything and couldn't find the problem..... I took repeater apart....using a simplex repeater (parrot) on both radios ...I'm able to transmit and receive from 5-7 miles (same antenna).... physically going on road trips with my hand held

 

I think its the duplexer....notch 4 cavity. Looks like it is tuned for both .575 and .600.... plus made in china...

I am saving up to get an American made duplexer but in the mean time, I just traded a radio for another Chinese duplexer,  new and 6 cavity, that is being tuned to .575 specifically.

 

Also, In the mean time I just ordered all new coax and adapters from dx engineering . Double shielded antenna coax and jumpers. Plus waterproofing...So I'm going to take the time to upgrade wiring... dx engineering 400max coax and silver plated brass connectors.

 

Plus I just had an idea. I have a small DC/AC mini fridge (for tailgating, weighs 10lbs) I never used it.

I'm using it to house the whole repeater... I all fits and will keep the tx radio, amp, power supply cool, plus it looks kinda cool. I started building an isolation box (copper lined) for the rx radio, inside 2nd shelf. Also thinking about a preamp circuit....

 

Thanks for all the help!

will keep you posted

Thanks!

301

[berkinet]

...I think its the duplexer....notch 4 cavity. Looks like it is tuned for both .575 and .600.... plus made in china...

I am saving up to get an American made duplexer...

I agree it is probably the duplexer. But, I think it is a little unfair blaming the problem on the country of manufacture. There are at least 10s of thousands of these cheap duplexers in use and they do work (for some definition of "work"). The problem is not where they were made, but the basic, notch-only design. Additionally, in the truly low cost products, the tuning parts are cheap and likely to fail. But, again, cheap is cheap, regardless of who made it or where.

 

If you want better performance, you will need a notch+band-pass duplexer, and those simply cost more, regardless of where they are made.

[wqzw301]

Berkinet,

 

Are notch band pass duplexers supposed to be tuned to a specific frequency set?? I see a lot of them sold with a range and no mention of being tuned like notch only duplexers.

p.s love Marcus Aurelius.. Great quote!

[WRAF213]

All duplexers require tuning; the range just says where the notch and/or pass frequency can be set within. The pass is tuned to your repeater's receive frequency (467.xxx), and the notch is tuned to the transmit frequency (462.xxx). The pass filter attenuates out-of-band signals; the notch attenuates the repeater's own transmission. Both characteristics are frequency-dependeny, and since the duplexer filters both the received signal and the repeater's transmitted signal, there's two different frequencies to take into account.

 

I wouldn't run any receive preamp without bandpass cavities in front of it; it'd be very sensitive to desensitization and intermod otherwise.

[Radioguy7268]

Also to add: I see by the callsign that the OP is located in NYC, and I'll assume that the repeater is on the rooftop of a building in the NYC area. There's a ton of RF energy in and around NYC. A Notch style duplexer is designed to be decent protection against the repeater's own frequencies. An inexpensive Notch style duplexer is NOT good at high concentrations of RF - such as at a mountaintop repeater site, or at a downtown urban area with tons of transmitters and intermod.

 

A duplexer should absolutely be tuned to a specific pair of frequencies. I'll avoid arguing over how some people try to cover the entire GMRS range with one single duplexer. If they're doing it, they're not doing it very well. Putting a UHF cavity filter on the receive side of the duplexer (between the high side duplexer connection and the actual receiver) would help to deaden down some of the RF noise that might otherwise overload the front end of the receiver. I would also avoid putting a pre-amp on a setup like this. You're probably just going to be amplifying noise - as much or more than your desired signal.

 

I have bought (and tested) a few of the Chinese duplexers off eBay. The quality of equipment and tuning varies. Generally, you're getting what you pay for. The better units from China tested out as good as most compact notch style duplexers I've seen from Sinclair or Celwave. I would not recommend using a notch style duplexer at a High RF site location - as mentioned. If you can't afford the real deal Bandpass/Bandreject Duplexer, then try to get some tuned bandpass cavities/cans.

[wqzw301]

Radioguy7268,

 

I'm in Brooklyn very south and east, no buildings just houses, by the water... Very little rf interference. The only uhf rf 70cm is the nypd / fire / ems repeaters on a couple of telephone poles and vhf from Airplanes, Kennedy Airport and marine channels.  People don't even have driveway door remotes.... Nearest cell tower is 1 mile. But lots of above the ground electrical wire on telephone poles.... We have about 3 gmrs repeaters and 5 ham 70cm repeaters. But Brooklyn is huge... We can fit 2 1/2 London's or Berlin and France together inside Brooklyn..The repeaters are all spaced far apart. It's not like Manhattan at all. We have a saying in Brooklyn - Keep Brooklyn low and local.... No tall buildings and no Wal-Mart.

My antenna is 45ft high. which is 20 ft over my house. Only a couple of drive thru about 3 miles away that broadcast on .5 watts murs. Just mom and pop stores that most don't even take debit card..... I'm in the sticks of Jamaica Bay...I'm by a 25 square mile national park made up of wetlands sparse trees.

I work in Manhattan and can hit my repeater 20 air miles from the 28 floor roof deck my friend is the super of...5 watt hand held.