Hello all, i have a Hospital that is using a new CDM700 Repeater. This is a UHF Repeater Freq. RX 406.8375 and TX 408.5375 TPL 156.7. The Repeater is working in top order, will work for a couple of days or so, then they will get alot of static and interferance intermod. I notice that they are not using any type of filter or anything with there system. I was wondering is there a way i can correct this for them, if there is a filter or something i can get for this system so they don't have this problem anymore, i would appreciate the make and model of what ever is sugguested. Also they have a external duplexer, would the cabling from the repeater to the duplexer if dirty or defected cause this problem also..
Thanks again for all your help guys,
john
Repeater static problem.
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johnny1225
- Posts: 229
- Joined: Thu Jul 22, 2004 8:27 am
Well, I think the first step would be to manage to be on-site when the interference occurs. Once you're hearing it, hook the repeater antenna to your Spectrum Analyzer of choice & see if you can see the offending carrier. Sometimes, it's a combination of two carriers, one whose 2nd harmonic minus the other carrier equals your frequency. It can get more complicated, hopefully it isn't in your case.
It's hard to say beyond that...certainly check to see if the build quality of the cabling is good...I seriously doubt the duplexer itself is at fault, especially if it tests ok for desense & whatnot on your service monitor.
Are you sure it's coming through the repeater (ie: does everyone hear the interference, or is it maybe localized to a couple of areas within the building)? Is this the same hospital which formerly had an MSR2000 & you switched it to the CDM700? If so, is this a new problem, or did it always exist? Nothing worse than a customer living with a problem for years, then blaming it on the new equipment & expecting you to 'fix' it.
Todd
It's hard to say beyond that...certainly check to see if the build quality of the cabling is good...I seriously doubt the duplexer itself is at fault, especially if it tests ok for desense & whatnot on your service monitor.
Are you sure it's coming through the repeater (ie: does everyone hear the interference, or is it maybe localized to a couple of areas within the building)? Is this the same hospital which formerly had an MSR2000 & you switched it to the CDM700? If so, is this a new problem, or did it always exist? Nothing worse than a customer living with a problem for years, then blaming it on the new equipment & expecting you to 'fix' it.
Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.
Welcome to the /\/\achine.
Welcome to the /\/\achine.
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johnny1225
- Posts: 229
- Joined: Thu Jul 22, 2004 8:27 am
No this is not the same hospital, they always had this CDM700 Repeater and has complained about it for a while now. It happens anywhere in the Hospital, not just certain locations. It seems to come and go, like it will be bad in the morning, but good in the afternoon, or vise versa.. Any help you can pervide would be very helpful to me.....
johnny
johnny
Well then, do what I suggested. If you do find an offending carrier, you'll need to get Industry Canada involved...good luck with that. If you do not have the proper equipment (or don't know how to use it properly), then you can call them to determine the problem themselves. If they're anything like the guys around here, you have a nice long wait ahead of you before anything gets done.johnny1225 wrote:No this is not the same hospital, they always had this CDM700 Repeater and has complained about it for a while now. It happens anywhere in the Hospital, not just certain locations. It seems to come and go, like it will be bad in the morning, but good in the afternoon, or vise versa.. Any help you can pervide would be very helpful to me.....
johnny
Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.
Welcome to the /\/\achine.
Welcome to the /\/\achine.
Trying to evaluate a situation like this from a distance is really an exercise in guesswork, but . . .
When you report that it "comes and goes," a light comes on that says you should have a really good tech shop take a look at the spec and tuning of your resonant equipment, and the environment that it lives in. A separation of less than 2 mHz is tight for a UHF duplexer, and if it sees wide swings in temperature and humidity, it could well be that it is allowing your transmitter to desense your receiver.
Bench tuning a duplexer is fine, but in a tight situation, only final tuning at the site and in the configuration in which it will operate assures that the duplexer is tuned with the cables and loads it will operate with.
When you report that it "comes and goes," a light comes on that says you should have a really good tech shop take a look at the spec and tuning of your resonant equipment, and the environment that it lives in. A separation of less than 2 mHz is tight for a UHF duplexer, and if it sees wide swings in temperature and humidity, it could well be that it is allowing your transmitter to desense your receiver.
Bench tuning a duplexer is fine, but in a tight situation, only final tuning at the site and in the configuration in which it will operate assures that the duplexer is tuned with the cables and loads it will operate with.
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chartofmaryland
- Batboard $upporter
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How close is the "hospital" to the line. There happens to be acouple of users not to far from the line using quite high power on frequencies close to the ones you are having problems with...
CHART
CHART
If the lights are out when you leave the station and then come on the second you key up, you know you have enough power.
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Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
Repeater static problem.
Hello John,
The only commercial manufacture of duplexers that can handle such a narrow Tx to Rx frequency spacing is Phelps-Dodge/Cellwave/RFS Model # PD696-4. These duplexers can be spaced down to 1 MHz @ -70 dB, as the Tx to Rx frequency spread increases to 2 MHz @ -90 dB (Signal / Noise rejection).
I spent several weeks researching this issue a couple years ago for /\/\ Schaumburg. These duplexers were to be sold in conjunction with the UHF T5365A Quantar Base Station / Repeaters. The minimum Tx to Rx frequency spread was 1.95 MHz for a U.S. Government customer in the 406-433 MHz Range 1 band plan.
If you don't have these duplexers and take a standand set designed for a 5 MHz Tx to Rx spread, the Notches will not align causing major changes in the ability to provide the minimum -70 dB rejection requirements and you may end up with -40 to -50 dB rejection which isn't enough. First you won't be able to tune the Notches correctly without opening up the filter cans and modifying the internal matching networks which probably would void any warantee. Secondly, you could cause internal arcing with voltage built ups and impedance mismatches.
Since this has been an ongoing problem ... I'd sure like to know which sales person sold and co-ordinated this frequency pair?
How far is this customer's repeater located from the U.S. / Canadian border?
Is the repeater located in an uncontrolled temperature enviroment .... such as a mechanical penthouse?
What are the /\/\ published electrical specification (in a service manual) for Tx and Rx noise, intermod, adjacent channel rejection?
Is the analog repeater programmed for 25/30 kHz or 12.5/15 kHz Channel Spacing since the DOC licensed it on a splinter frequency pair?
What type of RF coaxial cables are connected between the repeater and the duplexers?
RG-58/U, RG-8/U, RG-213/U, RG-8214, RG-400/U, RG-142/U, RG-214/U (Double Shielded) or 1/4" or 3/8" 50 Ohm Andrews Heliax RF coaxial cable?
What type of RF coaxial connectors are used?
Are the RF connectors Silver Plated with Gold center pins?
What type of a vertical gain antenna is used?
How high is the antenna mounted H.A.A.T?
Who performmed the last alignment on all of the individual components that make up this repeater?
Possibly the customer is expecting his CDM700 Base Station / Repeater to do something it's not designed to perform.
More questions than answers so I think you've got your work assignment cut out for you.
Dan
The only commercial manufacture of duplexers that can handle such a narrow Tx to Rx frequency spacing is Phelps-Dodge/Cellwave/RFS Model # PD696-4. These duplexers can be spaced down to 1 MHz @ -70 dB, as the Tx to Rx frequency spread increases to 2 MHz @ -90 dB (Signal / Noise rejection).
I spent several weeks researching this issue a couple years ago for /\/\ Schaumburg. These duplexers were to be sold in conjunction with the UHF T5365A Quantar Base Station / Repeaters. The minimum Tx to Rx frequency spread was 1.95 MHz for a U.S. Government customer in the 406-433 MHz Range 1 band plan.
If you don't have these duplexers and take a standand set designed for a 5 MHz Tx to Rx spread, the Notches will not align causing major changes in the ability to provide the minimum -70 dB rejection requirements and you may end up with -40 to -50 dB rejection which isn't enough. First you won't be able to tune the Notches correctly without opening up the filter cans and modifying the internal matching networks which probably would void any warantee. Secondly, you could cause internal arcing with voltage built ups and impedance mismatches.
Since this has been an ongoing problem ... I'd sure like to know which sales person sold and co-ordinated this frequency pair?
How far is this customer's repeater located from the U.S. / Canadian border?
Is the repeater located in an uncontrolled temperature enviroment .... such as a mechanical penthouse?
What are the /\/\ published electrical specification (in a service manual) for Tx and Rx noise, intermod, adjacent channel rejection?
Is the analog repeater programmed for 25/30 kHz or 12.5/15 kHz Channel Spacing since the DOC licensed it on a splinter frequency pair?
What type of RF coaxial cables are connected between the repeater and the duplexers?
RG-58/U, RG-8/U, RG-213/U, RG-8214, RG-400/U, RG-142/U, RG-214/U (Double Shielded) or 1/4" or 3/8" 50 Ohm Andrews Heliax RF coaxial cable?
What type of RF coaxial connectors are used?
Are the RF connectors Silver Plated with Gold center pins?
What type of a vertical gain antenna is used?
How high is the antenna mounted H.A.A.T?
Who performmed the last alignment on all of the individual components that make up this repeater?
Possibly the customer is expecting his CDM700 Base Station / Repeater to do something it's not designed to perform.
More questions than answers so I think you've got your work assignment cut out for you.
Dan
SlimBob, I have to agree 100%, the antenna IS the most important part of a repeater. Most of the "less expensive" antennas do not duplex worth crap, and get worse as the antenna
weatheres. They are just a piece of #18 gauge wire with a few coils wound in, just like a mobile antenna, but inside a plastic housing.
weatheres. They are just a piece of #18 gauge wire with a few coils wound in, just like a mobile antenna, but inside a plastic housing.