I have two MSF5000 side by side. One is on 461 MHZ and the other on a 443 freq. Both are using a AAR preamp and the IF signal "switch 2 on metering panel" has always lied around 15-17 uV on the meter wich makes for great sensitive receievers. All of a sudden though the ham machine's noise floor has jumped to about 25-27 uV on the meter and not sure what has happened. The 461 MHz MSF5000 is still at 15-17. I switched antennas and the noise floor went even higher on the ham machine. Does anyone know if a going-bad msf5000 power supply can do that? When I unplug the preamp from either machine the noise floor is at 10 on the meter on either machine without any antenna hooked up to them. So the preamp isn't bad. I am pulling my hair out. Someone local said maybe something in the air close to you is causing broadband noise on the input.
anyone have any ideas?
Site noise floor jumped up on MSF5000
Moderator: Queue Moderator
Re: Site noise floor jumped up on MSF5000
To all trying to help me, I just switched the meter panel to position #3 and normally the Mixer Local Oscillator should be reading at 26, the effected msf5000 is showing just about 0 now. I have a spare msf5000 how do I go about getting the local oscillator fixed?
Re: Site noise floor jumped up on MSF5000
From the simple comments that you have made, I would expect that a new transmitter has been added to
your location or in the near area. You now have the pleasure of trying to find what has caused the issue.
Many times, the addition of a pre-amp will cause more problems than they are worth. They are wide band
devices that don't care what the signal is or where it is. They will amplify it all. You may be forced into
installing a band pass cavity ahead of the amp to limit just what it is trying to amplify. This should be done
anyway on a repeater installation. This way your only trying to amplify just the small bandwidth right around
the repeater input frequency and not all the garbage around it for several megs.
Jim
your location or in the near area. You now have the pleasure of trying to find what has caused the issue.
Many times, the addition of a pre-amp will cause more problems than they are worth. They are wide band
devices that don't care what the signal is or where it is. They will amplify it all. You may be forced into
installing a band pass cavity ahead of the amp to limit just what it is trying to amplify. This should be done
anyway on a repeater installation. This way your only trying to amplify just the small bandwidth right around
the repeater input frequency and not all the garbage around it for several megs.
Jim
KF4LZA wrote:I have two MSF5000 side by side. One is on 461 MHZ and the other on a 443 freq. Both are using a AAR preamp and the IF signal "switch 2 on metering panel" has always lied around 15-17 uV on the meter wich makes for great sensitive receievers. All of a sudden though the ham machine's noise floor has jumped to about 25-27 uV on the meter and not sure what has happened. The 461 MHz MSF5000 is still at 15-17. I switched antennas and the noise floor went even higher on the ham machine. Does anyone know if a going-bad msf5000 power supply can do that? When I unplug the preamp from either machine the noise floor is at 10 on the meter on either machine without any antenna hooked up to them. So the preamp isn't bad. I am pulling my hair out. Someone local said maybe something in the air close to you is causing broadband noise on the input.
anyone have any ideas?
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Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
Re: Site noise floor jumped up on MSF5000
If you find where the interference signal is, I prefer a Notch Filter to a Band Pass Filter providing it's not 100kHz or closer. Then you'll be required to purchase a Crystal Filter.
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The Pager Geek
- Posts: 1250
- Joined: Fri Jun 21, 2002 10:31 pm
- What radios do you own?: Disney FRS
Re: Site noise floor jumped up on MSF5000
Have a spectrum analyzer handy?KF4LZA wrote:To all trying to help me, I just switched the meter panel to position #3 and normally the Mixer Local Oscillator should be reading at 26, the effected msf5000 is showing just about 0 now. I have a spare msf5000 how do I go about getting the local oscillator fixed?
tpg
Experienced Provider of Useless Information
Re: Site noise floor jumped up on MSF5000
KF4LZA could have the 'whisker' problem in the MSF5000.
There is much posted on the whisker problem here on BatBoard. Use the search to find it.
Basically the whiskers grow in the RX helical filters in the mixer/ injection stage and detune the receiver as the meter reading(s) may indicate.
There is much posted on the whisker problem here on BatBoard. Use the search to find it.
Basically the whiskers grow in the RX helical filters in the mixer/ injection stage and detune the receiver as the meter reading(s) may indicate.
Re: Site noise floor jumped up on MSF5000
My two bits worth:
With out inspecting your installation, I cannot tell you exactly what your problem might be.
I think that the first thing that I would do is do a thorough check out of your station.
CLB stations need to have the electrolytic caps in the 5V power supply changed.
The originals were very short lived, the nature of the switching supply design causes dielectric heating, so the caps do not last as long a caps not in a switching supply.
There is an often ignored cap on the interconnect board under the casting that also needs to be replaced if not already done.
(+5V to receiver on CLB, CXB has a dedicated +5V supply on the interconnect board.)
Often a squeal is observed on the repeat audio caused by failing caps.
Your trouble shooting tree just terminated at the no meter 3 step. Most likely it has "whiskers" in the injection filter which have been extensively written about. Meter 3 measures the DC bias from one of the mixer diodes on the mixer board which is mounted on top of the RF preselector. The bias on the other mixer can be measured directly on the board. There is an opening that is accessible with the cover removed. by the way, the receiver can oscillate with the cover off, so do not expect meaningful RF measurements with the cover removed.
Although meter 3 problems are usually caused by the plating whiskers, there can also be problems with the injection amplifier. The early CLB has no heat sink on the transistor, I have had these fail.
I have no idea how your RF is connected, filters, etc. With 40 years of trouble shooting sites, I find that one of the most often self induced problems is the addition of too much RF gain.
Having the front end mixer, and the IF limiters in saturation does not improve the system performance.
While you might observe a minor increase in talk in range, you might also not notice that other problems have surfaced, such as interference, or intermittent receive operation due to noise from other transmitters, such as adjacent channel mobiles. If the amplifier makes a big difference, you have other issues, bad cables, front end, antenna etc.
There is a procedure for measuring site noise, and desensitization.
I have it on a word document, from when I used to teach other techs how to do site work.
(Free for the asking)
As we were taught in radar school "you cannot receive below the grass"
Amplifiers are a very specific cure for a specific problem. Amplifiers amplify noise as well as the signal, as well as have noise of their own. Your MSF in the UHF range should be about -117 db/12dbSINAD. Your site noise level is likely in this range.
Meter two is not a very good diagnostic tool. You need to use the "effective sensitivity" procedure to establish the site noise floor at the instant you are measuring it, attenuate the output of the amplifier for best effective sensitivity.
You may find that the amplifier is of little or no real advantage.
Effective sensitivity is the bench test sensitivity minus the site noise measurement.
With out inspecting your installation, I cannot tell you exactly what your problem might be.
I think that the first thing that I would do is do a thorough check out of your station.
CLB stations need to have the electrolytic caps in the 5V power supply changed.
The originals were very short lived, the nature of the switching supply design causes dielectric heating, so the caps do not last as long a caps not in a switching supply.
There is an often ignored cap on the interconnect board under the casting that also needs to be replaced if not already done.
(+5V to receiver on CLB, CXB has a dedicated +5V supply on the interconnect board.)
Often a squeal is observed on the repeat audio caused by failing caps.
Your trouble shooting tree just terminated at the no meter 3 step. Most likely it has "whiskers" in the injection filter which have been extensively written about. Meter 3 measures the DC bias from one of the mixer diodes on the mixer board which is mounted on top of the RF preselector. The bias on the other mixer can be measured directly on the board. There is an opening that is accessible with the cover removed. by the way, the receiver can oscillate with the cover off, so do not expect meaningful RF measurements with the cover removed.
Although meter 3 problems are usually caused by the plating whiskers, there can also be problems with the injection amplifier. The early CLB has no heat sink on the transistor, I have had these fail.
I have no idea how your RF is connected, filters, etc. With 40 years of trouble shooting sites, I find that one of the most often self induced problems is the addition of too much RF gain.
Having the front end mixer, and the IF limiters in saturation does not improve the system performance.
While you might observe a minor increase in talk in range, you might also not notice that other problems have surfaced, such as interference, or intermittent receive operation due to noise from other transmitters, such as adjacent channel mobiles. If the amplifier makes a big difference, you have other issues, bad cables, front end, antenna etc.
There is a procedure for measuring site noise, and desensitization.
I have it on a word document, from when I used to teach other techs how to do site work.
(Free for the asking)
As we were taught in radar school "you cannot receive below the grass"
Amplifiers are a very specific cure for a specific problem. Amplifiers amplify noise as well as the signal, as well as have noise of their own. Your MSF in the UHF range should be about -117 db/12dbSINAD. Your site noise level is likely in this range.
Meter two is not a very good diagnostic tool. You need to use the "effective sensitivity" procedure to establish the site noise floor at the instant you are measuring it, attenuate the output of the amplifier for best effective sensitivity.
You may find that the amplifier is of little or no real advantage.
Effective sensitivity is the bench test sensitivity minus the site noise measurement.
Aloha, Bernie
Re: Site noise floor jumped up on MSF5000
To my surprise, it was one of our GR1225 repeaters about 300 feet away from the msf5000 station that caused the noise floor jump! Even with the 1225 not transmitting, it was occilating broadband noise all up and down the 440-460 area. I unplugged the 1225 from the wall and it went away along with the increased noise floor. Coinsidently, the users on the 1225 system complained to me about their radios not working well at the same time that the noise floor shot up, I just didnt put the two and two together. I suspect the 1225 has a bad PA or what not and because it was throwing spurs all over the place, the receive on it went to crap as well. I ha ve another 1225 on order.
what a weird phenomena...
i still not have any reading on meter #3 however my receive is great on the msf5000 and the noise floor is going. Portables can work the repeater about 12 miles away from the site that is only 100ft up from the ground...
what a weird phenomena...
i still not have any reading on meter #3 however my receive is great on the msf5000 and the noise floor is going. Portables can work the repeater about 12 miles away from the site that is only 100ft up from the ground...
Re: Site noise floor jumped up on MSF5000
My two bits worth:
Today your radio receives, perhaps tomorrow it will not.
Sort of like driving a car with loud metallic knocking noises and smoke indicate you are about to become a pedestrian.
A downward trend of meter 3 indicates the "Crystal Growth" problem. One member posted a beautiful picture of a filter. Looked like spider webs. Just touching one of the alignment slugs could cause it to fail completely.
Meter 3 is not critical, does not appear to effect receiver performance. Should be about half scale or more. The reason for high meter 3 is that the injection is at 0DBM , much higher than usual receivers of the day. The engineer that designed it told me it is so high to eliminate spurious responses.
Then you could go for years. Perhaps the metering circuit is faulty.
Today your radio receives, perhaps tomorrow it will not.
Sort of like driving a car with loud metallic knocking noises and smoke indicate you are about to become a pedestrian.
A downward trend of meter 3 indicates the "Crystal Growth" problem. One member posted a beautiful picture of a filter. Looked like spider webs. Just touching one of the alignment slugs could cause it to fail completely.
Meter 3 is not critical, does not appear to effect receiver performance. Should be about half scale or more. The reason for high meter 3 is that the injection is at 0DBM , much higher than usual receivers of the day. The engineer that designed it told me it is so high to eliminate spurious responses.
Then you could go for years. Perhaps the metering circuit is faulty.
Aloha, Bernie
Re: Site noise floor jumped up on MSF5000
Regarding whiskers and no M3 reading: I had a UHF station with no M3. Anyone who's moved an MSF station by more than 10 MHz knows what a royal P.I.T.A. it is to find the slightest bit of meter movement when adjusting these coils, so I disassembled the station, removed the mixer coil assembly, and connected it to my spectrum analyzer. I figured I could at least get the coils roughly adjusted. I saw nothing at all over the entire 0-1.5 GHz range.
I popped the rear cover off the assembly. I cleaned everything off, although I didn't see any whiskers inside. Not all assemblies have the problem. If it's got a shiny tin coating inside, then it could; if it has a dull aluminum coating, it probably won't. The later models are dull-coated.
A closer inspection showed the short wire lead that went to the output jack had become unsoldered from the nearby coil. I could see the nice wire-shaped indentation in the solder blob where the wire should have been attached. I pushed it back into position (only a few thousandths of an inch) and the output signal came right back. A quick touch with the soldering iron and a dab of solder fixed it right up. I suspect it just was a cold solder joint from the factory, and chose this moment to finally break loose. I bet it worked some of the time too.
I've got a 900 MHz station with the same symptom, but this one did show some M3 reading that quit as I was tuning it. I'll be pulling the coil assembly later this week.
Bob M.
I popped the rear cover off the assembly. I cleaned everything off, although I didn't see any whiskers inside. Not all assemblies have the problem. If it's got a shiny tin coating inside, then it could; if it has a dull aluminum coating, it probably won't. The later models are dull-coated.
A closer inspection showed the short wire lead that went to the output jack had become unsoldered from the nearby coil. I could see the nice wire-shaped indentation in the solder blob where the wire should have been attached. I pushed it back into position (only a few thousandths of an inch) and the output signal came right back. A quick touch with the soldering iron and a dab of solder fixed it right up. I suspect it just was a cold solder joint from the factory, and chose this moment to finally break loose. I bet it worked some of the time too.
I've got a 900 MHz station with the same symptom, but this one did show some M3 reading that quit as I was tuning it. I'll be pulling the coil assembly later this week.
Bob M.