As all of you almost already know I have my trusty model 38 connected to the MSF digital station. It has an issue of clipping the audio ands causing the signal to drop and the courtesy beep to repeatidly come on during a conversation. I have worked through some of the adjustments, but it becomes a sacrifice of audio vs. signal.
Any thoughts, Rob
Zetron 38 Audio Clipping Problem.
Moderator: Queue Moderator
You need a series resistor in the Z38 audio path into the MSF modulation circuit. 10K ohms minimum to 47K ohms better, this adds some isolation also. If you use the PL or DPL out of the 38, it also needs a series resistor. These resistors need to be located at the MSF logic/command board where they are "tied in" to the circuit board.
I usally feed the audio from the 38 thru the limmiter IN the MSF so I do not get a over-deviation condition. The PL or DPL output from the 38 is very stable and can be feed directly into the modulation summing circuit in the MSF, you NEED the series resistor there.
I usally feed the audio from the 38 thru the limmiter IN the MSF so I do not get a over-deviation condition. The PL or DPL output from the 38 is very stable and can be feed directly into the modulation summing circuit in the MSF, you NEED the series resistor there.
Will:
What you suggest is exactly what the 38MAX manual recommends for an MSF - except they use 33k.
However - while this *might* solve an audio clipping problem, I will suggest it is not his TX and PL/DPL out since the courtesy beep has nothing to do with those lines. It is controlled by the disc input and/or COS.
I am interested in this as our group is using 38MAX controllers on several MSR2000 UHF stations and one site seems to have the same problem - but it does not seem related to not related to audio level. We swapped out stations (MSR/controller combination) at one point with another MSR/controller and we still get the same problem.
Sympton: Even during strong signal conditions, with little multipath, the controller will send a courtesy tone - almost like there was a fade on the receiver and the COS dropped (except we cannot detect one). I think the contoller also momentarily mutes the audio when it sends the courtesy tone (which is likely by design). Can be very annoying.
The Zetron manual only recommends a 10k in th encode out for the MSR.
Since our issue almost seems to be related to the site - I am suspecting that we might have some very intermittant and short-duration (millisecond-range) interfrence that might be hitting us. I assume you have tried using a load on the antenna to isolate the receiver from external influences?? We have not yet tried this.
So - I have no solutions for you, only consolation. Please let us know what you find.
What you suggest is exactly what the 38MAX manual recommends for an MSF - except they use 33k.
However - while this *might* solve an audio clipping problem, I will suggest it is not his TX and PL/DPL out since the courtesy beep has nothing to do with those lines. It is controlled by the disc input and/or COS.
I am interested in this as our group is using 38MAX controllers on several MSR2000 UHF stations and one site seems to have the same problem - but it does not seem related to not related to audio level. We swapped out stations (MSR/controller combination) at one point with another MSR/controller and we still get the same problem.
Sympton: Even during strong signal conditions, with little multipath, the controller will send a courtesy tone - almost like there was a fade on the receiver and the COS dropped (except we cannot detect one). I think the contoller also momentarily mutes the audio when it sends the courtesy tone (which is likely by design). Can be very annoying.
The Zetron manual only recommends a 10k in th encode out for the MSR.
Since our issue almost seems to be related to the site - I am suspecting that we might have some very intermittant and short-duration (millisecond-range) interfrence that might be hitting us. I assume you have tried using a load on the antenna to isolate the receiver from external influences?? We have not yet tried this.
So - I have no solutions for you, only consolation. Please let us know what you find.
intermod
-
apco25
- Posts: 2685
- Joined: Tue Oct 30, 2001 4:00 pm
- What radios do you own?: APX / Astro 25 / Harris
We used to get this same problem on our old 450 channel at the park.
Old 38A tied to Standard repeater.
Any weak signal condition would force the god awul courtesy tone to come up and over ride the audio creating "holes"
We never could figure what to do to stop it. Doesn't matter now we put 4 new kenwood repeaters up last month.
Old 38A tied to Standard repeater.
Any weak signal condition would force the god awul courtesy tone to come up and over ride the audio creating "holes"
We never could figure what to do to stop it. Doesn't matter now we put 4 new kenwood repeaters up last month.
"Some men just don't know their limitations"
Message From Zetron Tech Support
I posed the courtesy tone problem to Zetron Support. Here is their suggestion:
"After reading the description of your problem and reading the BATLABS messages, I believe what you are seeing is a loss of decode. This can occur if the receive audio is set to high and the PL/DPL signaling gets clipped off in the audio op-amp or if an out of face or different PL/DPL tone is being received by the Model 38A/ 38Max. This is known as INTERMOD. To verify the audio receive audio level is set correctly use your service monitor to send the 38A or 38Max a 1KHZ tone at 60% Channel deviation, about 3 KHZ for a 25K wide band channel. Put an oscilloscope on Pin-1 of IC U-7. Adjust R-13, the Audio Input pot, for 1VPP on the scope. This centers the receive audio level in the linear operating range of the op-amp. Then set the repeat TX Audio for 3KHZ DEV of the 1 KHZ tone and set the PL tone for 750 HZ DEV. This should set the total deviation to 3.75 KHZ deviation with the Test tone and PL tone.
The purpose of the 10 K ohm resistor in the PL/DPL encode line is that the input audio level requirement of the Coded Squelch input of the MSR2000 repeater is in the noise floor of the op-amps used in the 38A/ 38Max. The resistor allows us to raise out output level above the noise floor of the op-amps and not over drive the input to the station. Some cases of intermodulation have accrued when this resistor value was raised to high and the output from the 38A / 38Max has reached a level that has allowed it to bleed into the Disc Audio input lead into the 38A / 38Max causing phase cancellation of the PL/DPL tones. Some cases of intermodulation have been caused by grounding and shielding issues at sites allowing noise to be radiated between repeaters.
The Zetron Model 38 series repeater controllers have been out for over 15 years with over ten thousand repeater controllers having been sold. Customer calls to our Technical Support Center have usually been able to resolve most installation or operation issues. If you require more assistance in resolving installation, Programming or operational issues with You Zetron Model 38Max please call our Technical Support Staff at (425) 820 6363 ext 741 between 7:00 a.m. and 5:00 p.m. Pacific time, Monday through Friday."
This is a good example of why we purchased Zetron - I always got good technical support. We are going to look into this. Hope this helps.
Intermod
"After reading the description of your problem and reading the BATLABS messages, I believe what you are seeing is a loss of decode. This can occur if the receive audio is set to high and the PL/DPL signaling gets clipped off in the audio op-amp or if an out of face or different PL/DPL tone is being received by the Model 38A/ 38Max. This is known as INTERMOD. To verify the audio receive audio level is set correctly use your service monitor to send the 38A or 38Max a 1KHZ tone at 60% Channel deviation, about 3 KHZ for a 25K wide band channel. Put an oscilloscope on Pin-1 of IC U-7. Adjust R-13, the Audio Input pot, for 1VPP on the scope. This centers the receive audio level in the linear operating range of the op-amp. Then set the repeat TX Audio for 3KHZ DEV of the 1 KHZ tone and set the PL tone for 750 HZ DEV. This should set the total deviation to 3.75 KHZ deviation with the Test tone and PL tone.
The purpose of the 10 K ohm resistor in the PL/DPL encode line is that the input audio level requirement of the Coded Squelch input of the MSR2000 repeater is in the noise floor of the op-amps used in the 38A/ 38Max. The resistor allows us to raise out output level above the noise floor of the op-amps and not over drive the input to the station. Some cases of intermodulation have accrued when this resistor value was raised to high and the output from the 38A / 38Max has reached a level that has allowed it to bleed into the Disc Audio input lead into the 38A / 38Max causing phase cancellation of the PL/DPL tones. Some cases of intermodulation have been caused by grounding and shielding issues at sites allowing noise to be radiated between repeaters.
The Zetron Model 38 series repeater controllers have been out for over 15 years with over ten thousand repeater controllers having been sold. Customer calls to our Technical Support Center have usually been able to resolve most installation or operation issues. If you require more assistance in resolving installation, Programming or operational issues with You Zetron Model 38Max please call our Technical Support Staff at (425) 820 6363 ext 741 between 7:00 a.m. and 5:00 p.m. Pacific time, Monday through Friday."
This is a good example of why we purchased Zetron - I always got good technical support. We are going to look into this. Hope this helps.
Intermod
intermod
Zetron 38 clipping audio
[quote="N9LLO"]Make sure your reciever (and your users) are dead on frequency
and the users radio is not overdeviated and has the correct PL
deviation level.
Chris[/quote]
There is one more possibility to the cause of your problem. Zetron made a change to the firmware to help reduce this type of problem. You might try looking at the firmware revision on the PROM's in the 38. Contact Zetron and see if you might have one of the old revisions.
This was done years ago so it might not be your issue. But it is worth a check. Seems to me that change was made back in the late 80's. So unless the panel has been sitting around or someone was just ignoring the problem it may be way off.
Jim
and the users radio is not overdeviated and has the correct PL
deviation level.
Chris[/quote]
There is one more possibility to the cause of your problem. Zetron made a change to the firmware to help reduce this type of problem. You might try looking at the firmware revision on the PROM's in the 38. Contact Zetron and see if you might have one of the old revisions.
This was done years ago so it might not be your issue. But it is worth a check. Seems to me that change was made back in the late 80's. So unless the panel has been sitting around or someone was just ignoring the problem it may be way off.
Jim
Jim is correct, Zetron made a firmware change in the 90"s to what they call "ToneLock". The later version M38's have the upgrades and this helps.
Tone Lock does work, kind a hard to get one to talk off, and they respond to the reverse burst turn off much better.
Ask Zetron for the upgrade, a new prom and a couple of componets to change.
Tone Lock does work, kind a hard to get one to talk off, and they respond to the reverse burst turn off much better.
Ask Zetron for the upgrade, a new prom and a couple of componets to change.