MSR2000 VHF interference
Moderator: Queue Moderator
MSR2000 VHF interference
I have a MSR2000 VHF repeater that wants to stay keyed during delayed drop out with static bursts and unintelligible words or music. This seems to happen mostly during daytime and working hours and unusual weather or temperature changes. Rx-Tx split is only 285 kHz. No desense problem. No broadcast stations in town. I am looking for ideas for things to check on. I have thought about shortwave station on high IF frequency around 10.7 mHz, cable TV leakage, spurs from FM and TV receivers, or something from MARTI patch. Receive frequency is 153.890.
"The world runs on radio."
The Motorola factory duplexer used on the HB MSR2000 is only designed to work at T-R separations greater than 1.5 MHz. It is a six-cavity Celwave unit with the cans mounted horizontally on the rack shelf. The factory does not ship repeater stations with closer T-R spacings; an alternate duplexer can be purchased separately or you can skip the duplexer altogether and use two antennas with adequate isolation between them.
If your repeater station shipped directly from the Motorola factory on the present frequencies with the Motorola duplexer, talk to your dealer. On the other hand, if your station was converted to a repeater or had its frequencies reporogrammed after shipment, you need to have words with the person or agency who did the programming and/or provided the duplexer.
If your repeater station shipped directly from the Motorola factory on the present frequencies with the Motorola duplexer, talk to your dealer. On the other hand, if your station was converted to a repeater or had its frequencies reporogrammed after shipment, you need to have words with the person or agency who did the programming and/or provided the duplexer.
Karl - WA8NVW AFA5VB
SHARES + NCS
SHARES + NCS
-
N4DES
- was KS4VT
- Posts: 1234
- Joined: Thu Dec 25, 2003 7:59 am
- What radios do you own?: APX,XTS2500,XTL2500,XTL1500
It could be a TV amp that has gone spurious. We get those a lot in the summer time when the condo penthouses get really warm.
Also did you check the adjacent (15 KHz) off from your receive frequency?
If you have a radio or service monitor it maybe worthwhile to "T" off the receive side of the duplexer and have a listen around the RX freq for a while.
Mark
Also did you check the adjacent (15 KHz) off from your receive frequency?
If you have a radio or service monitor it maybe worthwhile to "T" off the receive side of the duplexer and have a listen around the RX freq for a while.
Mark
-
Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
MSR2000 VHF Interference
Your MSR2000 Base Station Repeater might be suffering from an Intermodulation mix. You've got to make sure that your equipment and/or RF site is free from external problems such as loose rain gutters, poor grounding system, defective coaxial cable/connectors and corroded door hinges on the building.
Is your repeater site co-located with other 2-way VHF equipment?
If so, What are the Tx frequencies of all the other stations?
How long has this problem been occurring at the site?
What type of coaxial feedline is used between the base station repeater and the antenna, RG-213/U, RG-214/U, LMR-400 or 1/2" Andrews Heliax and How long has this cable been in place, 1yr, 2yr, 5yr, 10yr or longer?
What type of an antenna is mounted on top tower and/or the building, i.e. open faced Dipole Co-linear array or a Fiberglass Co-linear? Who is the manufacture of the VHF antenna"
Have you checked the feedline RF connectors and Are they sealed with a good grade coaxial Vapor-Lock compound, 3M Tape and 3M Liquid Tape making them waterproof connections?
Since the MSR2000 uses TCXO driven oscillators, one for Tz and a separate one for Rx, Have you tried to get another TCXO, say about 50 or 100 kHz farther away from the Rx frequency and see if the problem continues?
The standard /\/\ duplexers can only be tuned for a 1.5 MHz Tx to Rx frequency separation. Most external 4 or 6 can cavity filter duplexers on High Band VHF can only be tuned down to .3 MHz separation for 70 dB Rejection. Are you feeding the MSR2000 into a Hybrid Cavity Combiner system?
Are you using any type of a receiver Pre-amplifier on this station, Internal or External?
Since this interference problem seems to be more intense with changing weather conditions, rain or snow. Have you checked the Forward and Reflected RF Power (Watts) during these conditions? What are you wattage readings during wet weather?
Are your RF Connectors Silver Plated with Gold center pins?
Are you using an Isolator/Circulator in your TX line configuration?
Have you checked your XMTR signal on a Spectrum Analyzer for spurious emissions and How many dB down are the spurs? To do this correctly you'll need a Spectrum Analyzer and a separate RF Signal Generator source.
Is your repeater cabinet and station Cad-Weld grounded to the metal support structure and/or tower?
Is your repeater system close to a big city or a RF radio Paging system?
What is the Height Above Average Terrian for the repeater's antenna?
Was the MSR2000 originally a Base Station then converted into a Repeater?
Have you been on-site while this problem occurs? If you have, Have you tried to insert a switchable dB RF attenuator in the receivers coaxial cable line and switched in 5, 10, 20, 25 dB attenuation to see what happens to the interference problem?
I have seen similiar RF interference problems like the one you have described takes time before you stumble on the culprit. But you must do your part first verifying your set up is in good working electrical condition and a proper system design before you can point the finger at anyone else.
Dan
Is your repeater site co-located with other 2-way VHF equipment?
If so, What are the Tx frequencies of all the other stations?
How long has this problem been occurring at the site?
What type of coaxial feedline is used between the base station repeater and the antenna, RG-213/U, RG-214/U, LMR-400 or 1/2" Andrews Heliax and How long has this cable been in place, 1yr, 2yr, 5yr, 10yr or longer?
What type of an antenna is mounted on top tower and/or the building, i.e. open faced Dipole Co-linear array or a Fiberglass Co-linear? Who is the manufacture of the VHF antenna"
Have you checked the feedline RF connectors and Are they sealed with a good grade coaxial Vapor-Lock compound, 3M Tape and 3M Liquid Tape making them waterproof connections?
Since the MSR2000 uses TCXO driven oscillators, one for Tz and a separate one for Rx, Have you tried to get another TCXO, say about 50 or 100 kHz farther away from the Rx frequency and see if the problem continues?
The standard /\/\ duplexers can only be tuned for a 1.5 MHz Tx to Rx frequency separation. Most external 4 or 6 can cavity filter duplexers on High Band VHF can only be tuned down to .3 MHz separation for 70 dB Rejection. Are you feeding the MSR2000 into a Hybrid Cavity Combiner system?
Are you using any type of a receiver Pre-amplifier on this station, Internal or External?
Since this interference problem seems to be more intense with changing weather conditions, rain or snow. Have you checked the Forward and Reflected RF Power (Watts) during these conditions? What are you wattage readings during wet weather?
Are your RF Connectors Silver Plated with Gold center pins?
Are you using an Isolator/Circulator in your TX line configuration?
Have you checked your XMTR signal on a Spectrum Analyzer for spurious emissions and How many dB down are the spurs? To do this correctly you'll need a Spectrum Analyzer and a separate RF Signal Generator source.
Is your repeater cabinet and station Cad-Weld grounded to the metal support structure and/or tower?
Is your repeater system close to a big city or a RF radio Paging system?
What is the Height Above Average Terrian for the repeater's antenna?
Was the MSR2000 originally a Base Station then converted into a Repeater?
Have you been on-site while this problem occurs? If you have, Have you tried to insert a switchable dB RF attenuator in the receivers coaxial cable line and switched in 5, 10, 20, 25 dB attenuation to see what happens to the interference problem?
I have seen similiar RF interference problems like the one you have described takes time before you stumble on the culprit. But you must do your part first verifying your set up is in good working electrical condition and a proper system design before you can point the finger at anyone else.
Dan
-
Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
VHF MSR2000 Interference
You mentioned that the station receiver has no desense. Exactly how did you measure and determine there wasn't any desense?
The /\/\ system planner for the MSR2000 VHF station refers to the station's standard receiver is only capable of 25/30 kHz channel spacing and I never recall seeing a SP Option for 12.5/15 kHz channel spacing.
Now why would I mention this? Well earlier today I went the FCC Rules & Regulations Part 90 and researched your receiver assigned frequency 153.890 MHz listed as PF Mobile (10 Watt Output limit). Then I looked at the nearest adjacent RF channels, they are 153.875 MHz and 153.905 MHz both listed as PL.
PF stands for Fire frequency and PL stands for Local Government Frequency and both of these channels are 15 kHz either side of the Fire Frequency. You may want to look at both of these frequencies as far as activity and if they are busy with radio traffic, you should check how much RF output the mobiles are using (limited to 10 Watts Output), what are the deviation levels set at, who co-ordinated the use of those frequencies and at what date?
Years ago there was a Field Modification Kit Option set up for a TFN1018 Crystal Filter to be inserted in the coaxial cable line for the Receiver's Carrier Frequency. This was designed & set-up for the sole purpose to reduce Intermodulation, Desense and adjacent channel noise to tighten up the receiver specifications. I don't know if the Crystal Filter is still available through AAD (NPD) 1-800-422-4210 any longer. If it is, you would need to order one specify the receiver carrier frequency of 153.890 MHz. I don't know if International Crystal Manufacturing offers any crystal filter option like /\/\ did.
Dan
The /\/\ system planner for the MSR2000 VHF station refers to the station's standard receiver is only capable of 25/30 kHz channel spacing and I never recall seeing a SP Option for 12.5/15 kHz channel spacing.
Now why would I mention this? Well earlier today I went the FCC Rules & Regulations Part 90 and researched your receiver assigned frequency 153.890 MHz listed as PF Mobile (10 Watt Output limit). Then I looked at the nearest adjacent RF channels, they are 153.875 MHz and 153.905 MHz both listed as PL.
PF stands for Fire frequency and PL stands for Local Government Frequency and both of these channels are 15 kHz either side of the Fire Frequency. You may want to look at both of these frequencies as far as activity and if they are busy with radio traffic, you should check how much RF output the mobiles are using (limited to 10 Watts Output), what are the deviation levels set at, who co-ordinated the use of those frequencies and at what date?
Years ago there was a Field Modification Kit Option set up for a TFN1018 Crystal Filter to be inserted in the coaxial cable line for the Receiver's Carrier Frequency. This was designed & set-up for the sole purpose to reduce Intermodulation, Desense and adjacent channel noise to tighten up the receiver specifications. I don't know if the Crystal Filter is still available through AAD (NPD) 1-800-422-4210 any longer. If it is, you would need to order one specify the receiver carrier frequency of 153.890 MHz. I don't know if International Crystal Manufacturing offers any crystal filter option like /\/\ did.
Dan
-
Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
MSR2000 VHF Interference
Let's revisit your MSR2000 receiver's interference problem as there may be a solution. I was surfing the internet a few weeks back and I found this infornation on a commercial website about Narrow Banding the older /\/\ radios for the 12.5 kHz Channels. You might call the OEM Com-Spec or send an email verifying the Narrow Band I.F. Crystal Kit will be compatible with your MSR2000 VHF Repeater's Receiver.
http://www.com-spec.com/index1.htm
Dan
http://www.com-spec.com/index1.htm
Dan