weird Zetron console audio issue,hanging up

[FatBoy]

Console experts,
I have a customer who is having multiple issues with their Zetron 4020. My in-house Zetron guy is out on FMLA for a bit. The frst issue is a weird RX audio issue on only a single channel. It is a air-band unicom frequency. Various tests indicate it is an external rf issue, but cannot see it on a spectrum analyzer. The issue seems to be local to the area as aircraft 15 minutes away cannot copy the noise, but aircraft just outside the facility can copy it. BUT, this noise only happens when someone is transmitting. Here are links to the 2 audio files:
http://www.mediafire.com/?jw3mnuujczg
http://www.mediafire.com/?bgqnewtzgjm

The 2nd issue is they have an EDACS radio that transmits fine from the console, but locks up the console for 4-10 seconds after the dispatcher has released the mic. This behavior is only on this EDACS channel. Radio is not programmed for dual head config.

My lack of experience with the Zetron line is really kicking my butt on this one. Any input? FatBoy

[Bill_G]

#1 - You can verify it is an externally caused noise by listening on a scanner. I suspect a strobe light. Generate a low level signal with your service monitor radiating into an ant to see if you can recreate the conditions. If not, have someone key a radio with silence for short periods while you try to zero in on the source.

#2 - You can verify by operating the radio locally to determine if it is a console or a radio problem.

[Jim202]

It almost sound like an old type crystal scanner with the local oscillator radiating enough signal to get
into the channel your trying to receive. I may be wrong and it turns out to be one of the newer type
scanners, but sure sounds like a scanner radiating.

Jim

Console experts,
I have a customer who is having multiple issues with their Zetron 4020. My in-house Zetron guy is out on FMLA for a bit. The frst issue is a weird RX audio issue on only a single channel. It is a air-band unicom frequency. Various tests indicate it is an external rf issue, but cannot see it on a spectrum analyzer. The issue seems to be local to the area as aircraft 15 minutes away cannot copy the noise, but aircraft just outside the facility can copy it. BUT, this noise only happens when someone is transmitting. Here are links to the 2 audio files:
http://www.mediafire.com/?jw3mnuujczg
http://www.mediafire.com/?bgqnewtzgjm

The 2nd issue is they have an EDACS radio that transmits fine from the console, but locks up the console for 4-10 seconds after the dispatcher has released the mic. This behavior is only on this EDACS channel. Radio is not programmed for dual head config.

My lack of experience with the Zetron line is really kicking my butt on this one. Any input? FatBoy

[FatBoy]

I did sweep the room where the radio is located, swept the actual antenna that the customer uses, also had a different outside antenna that I brought for testing. All came up clean for noise sources 10mhz either side of their assigned frequency. I did not sweep IF frequencies (awesome suggestion). Strobes will be fun to track down as facility is very near a downtown area. Customer has been dealing with this issue for several months since another facility (5 air minutes away) upgraded their dispatch position. Since said upgrade, that other facility has been unable to use same unicom frequency due to interference. Said other facility has just muted the unicom frequency at the console and never uses it. Just not used to signals that only appear when there is another active transmission on the same frequency. I can easily resolve intermod, desense, etc but this one has me earning my keep. Keep up the suggestions coming. I will schedule a sweep at the "other" facility" this week and report back. FYI, I am the third vendor on this, other shops have long since given up. FatBoy.

[Bill_G]

I think it is a form of intermod that you are chasing. That's why aircraft have to be close to hear it. Something is being energized when a transmitter comes up. But, you need to verify it with an external rcvr that is not attached to the console like a handheld scanner. Then you need to determine how much energy it takes to recreate the conditions by radiating a carrier with your service monitor. It's doubtful a service monitor has the horsepower to do it. More likely it will require a few watts like from another unicom. Then it's just a matter of df'ing the source. That's if it really is an externality. It could be on the phone line between the radio and console. You gotta work the problem, and get all the info you can.

[FatBoy]

I cannot hear it on my handheld on the roof near their console radio antenna, but they can hear it when I talk on my portable on the roof. The helos that are close can hear it from my portable, from the console, and from each other. I think my antenna on the portable needs to be better (read that as directional with good front/back). Trying to get the go-ahead for more funding on this thing. ......................Customer just told me that they had some strobe work done. And we are off................FatBoy

[Bill_G]

That's what I'm talking about. You should be able to hear it on your portable on the flightline when the console or an aircraft transmits if it is a mix product from an external device. You should have a little distance between you and the base station antenna. Several hundred yards or so. If you hear it when either the console or an aircraft talks, it is an intermod product. If you only hear it from the console, it's something else.

[FatBoy]

UPDATE:
Ok, determined that the strobes had zero effect. Also was able to idependently confirm that the other hospital facility is completely not at fault (although their tx/rx audio sounds bad!). Furthermore, was able to verify the noise IS being re-radiated outside of the facility (copied noise on my personal portable on the flight line 100m from customer's tower. Doubt it is IF related due to the number of different types of airband makes/models affected. Starting to look like one of the 20 800mhz freqs that is co-located is generating a IMD product. So, basically any rf on this airband freq that is radiated locally (within a few miles) is received and re-radiated by this site. I am making a small loop probe and am going to be poking around the site equipment with the Anritsu/IFR WHILE my assistant is on the flightline transmitting. The 800mhz site is set up as a fill-in site with panel antennas that only tx/rx about 120 degrees away from the facility. Developing some test procedures now. Unfortunately, I am not able to just unplug the 800mhz rf cables 1 at a time to see which one is the offender. Will advise, FatBoy.
ETA- 800mhz freqs went through rebanding AND the site went from 15 to 20 ch about the same time the problem started.

[Bill_G]

Excellent. So, you heard it in your portable on property a short distance away from the customer antenna confirming it is probably real IM. You could not hear it in your portable near the customer antenna on their rooftop when they keyed. However, keying your portable caused the noise in other rcvrs including the customer radio.

I need a clarification - were you on their roof when you keyed your portable? I'm attempting to understand why their simplex would swamp the IM product in your portable so it could not be heard, but was not swamped out by your portable in their rcvr.

If yes, what pwr is their transmitter at compared to your portable?

If no, can you conduct another aircheck from their roof with your portable?

Has their antenna been swapped out as a test yet?

[FatBoy]

Did swap out their antenna. Basically, I have determined that there is a sweet spot for making the interference and a similiar (but slightly different sweet spot for rx ing this interference. I believe this is due to the panel antennas mounted just above/below customers airband base antenna. The panels cover about a 120 degree arc. If I am on the back side of the panels, I can cause it, but I cannot hear it. If I am out in front of the panels with my radio receiving, the noise is much more pronounced on my rx (basically, it seems easy to "make" the noise from any direction, but the 800mhz panels really throw it back out strongest inside their arc. Will keep you updated. FatBoy.

[Bill_G]

Is there short tower section, or a wall all this stuff is mounted on? Any possibility of moving their antenna above and away (like 25ft above) the panel antennas? Have you enlisted the help of the site manager for the 800 system? Does the customer radio have an isolator on it, or at least a bandpass cavity?

[FatBoy]

Negative on moving the antennas. The panels are slightly beow the top of the tower on a horizontal platform, with the unicom a few feet above it. I do not think this is the issue becuase ANY close proximity rf (not just the base) on this frequency gets mixed in and re-radiated. I know there is no cavity or isolator on my customer's equipment. I will check the EDACS system (for both cavities and to find out which repeater is mixing and re-radiating this) during the next sweep. We are working with the system manager on an unrelated issue (poorly setup Zetron console-due to poorly setup base EDACS radios) and will dovetail this request. FatBoy

[ai4ui]

Had a problem with a VHF site several years back of an IM product that would intermittently appear very close to the input of a repeater when the repeater was transmitting (with the same PL). After a while, we tracked it down to the el-cheapo switching power supply battery maintainer for the starting battery on the standby generator. The battery maintainer would switch off and on periodically and would only create the IM product when it was in charge mode. Some ferrite beads on the power cord and output cord took care of it.

You may want to take a look at what is being used for the starter battery for the generator.

[FatBoy]

Will investigate the generator, but their backup power plant is something like 44MW and uses diesel/electric motors from railroad engines. Their fuel storage is somewhere near 20,000+ or so gallons and should last a few days. It is certainly one of the larger "sites" we service. FatBoy

[Bill_G]

Oh yeah. IM can come from all kinds of places including the fence around the compound, loose cross members on a tower, and abandoned antennas the next tower over on the same hilltop. They can be a devil to find. Almost makes you long for the good old days of full duplex VHF IMTS phones in logging trucks. No loose metal there.

[psapengineer]

This is kind of a shot in the dark but here are two thoughts...............

Here's the first one:

I've heard this kind of noise before when two AGC amplifiers are fighting each other. I know the console product has an AGC in it, does there happen to be another AGC somewhere in the line/system or a piece of the connectivity between the console or the radio that you don't control (like a leased telephone line)?

The two AGCs can pump against each other and "ring" like you're saying.

You might try reducing the Rx/incoming gain on the dual channel control card for that channel to see if it changes or resolves the problem. If your not familiar with level setting at least remember the number of "turns" that you make on the pot so that you can get back to where you started. Remember that its a dual card so half of the adjustments are for the "other" channel. Also, you will need to determine if the radio is controlled by two or four wires; they are two different pots on the card. Be sure the unused one is turned down. I put a piece of tape over all of the other pots that I'm not adjusting on the card just so that the twiddle stick doesn't get into the wrong hole; its very easy to do on that model.


The second is less easy to test for:

I've seen systems where the power supply gets sick and delivers marginal current, then, on voice peaks the switching power supply pumps some charge into the bus on a periodic basis and the audio; like you're hearing, is in the audible range since the switching frequency of the supply was in the same range.


Let us know what you find; it will be an interesting tidbit to file away for future reference.

Best Regards,
Bob

[Bill_G]

Bob - I'm pretty certain fatboy stated that helo's can hear it in their rcvrs when he transmits on his portable which should eliminate the console audio paths as the source of the odd sound.

[psapengineer]

Must have missed that in the thread.......
Bob

[FatBoy]

Swept the 20ch 800mhz EDACS system that is in the same room with the equipment. I did not find an issue, also had the EDACS tech turn off all of the channels (one by one) to make sure the mixer/oscillators went quiet (holy crap is the EDACS system noisy on RF!!!!!!!!)...........and no joy. Swept any/all CATV amps and fiber/media converters that I could locate. Have contacted the FCC as this has been determined to be a safety issue. Will advise once they contact me. FatBoy.

[FatBoy]

Solved the "Zetron hanging up on the EDACS radio" issue. The Orion was not programmed for dual-head operation as it was supposed to be. Fixed the programming and it is working fine. Still waiting to hear from the Friendly Candy Company. FatBoy.

[kb4mdz]

Sooo, who's the numnuttz that programmed the EDACS radio wrong? Or is he long gone out of the equation?

But why have a dual head Orion as a control station hanging off a console system?

Solved the "Zetron hanging up on the EDACS radio" issue. The Orion was not programmed for dual-head operation as it was supposed to be. Fixed the programming and it is working fine. Still waiting to hear from the Friendly Candy Company. FatBoy.

[FatBoy]

EDACS Radio was provided with a tone remote board from the Sherriffs Office (who owns the EDACS system). Moto tech who setup console bypassed the tone board and went straight to the radios accy connector (per Zetron manual). I just guess he bypassed the part where you needed it setup for dual head or "intermittent operation" would result (needed dual head to give console ability to channel change, volume control, using other radio features). UPDATE!!!! Fixed interference problem. Two very nice guys showed up from the FCC in a very well equipped Crown Vic. It took them a bit to understand the nature of the problem, but once they had a grasp on the issues at hand they solved it very quickly! Turns out, it was the other hospital that had just recently undergone a console change out. It looks like whenever the aviation radio at that facility rx'd a signal, it then went into tx mode for a period of time. I am not sure if it was radio programming, mis-wiring of the console equipment, or bad console/radio...........as soon as they shut it off, the problem ceased. Wished I was there to see the radio managers face when he got the message that the FCC was waiting for him downstairs! The major issue is we requested he shut the unit off early on in the troubleshooting (weeks ago), but he would just say "It is not us!" and hang up the phone. All of the equipment connected to his console sounds very poor on tx and his dispatchers are always telling people that they cannot be understood on the radio. Oh well. Same poop, different toliet..........FatBoy.

[FatBoy]

For futher clarification. EDACS radio is setup for dual head, but the console connected to the accy connectoer is considered the 2nd head....................just wanted to clarify. Thank you all for your interest. FatBoy.

[Bill_G]

I wondered about the other hospital, but wouldn't have imagined a radio doing what it did. I'm betting a console issue. Simplex radios just do not auto-repeat. The ultimate source of the problem would be interesting to understand.

[GMC]

Two very nice guys showed up from the FCC in a very well equipped Crown Vic. FatBoy.

Yea aren't those cars great........................ If it's like the one I saw when I had a problem it has a bunch of equipment for tracking in the middle between the front seats and you cant find a single antenna on the car.

[kb4mdz]

As we say in the South, it sounds like it's time for a "Come to Jesus meeting" with that radio manager - that next time someone calls requesting assistance, he'd better hop right to it and not be such an *ss about it.

That, and sounds like he needs a new radio shop that knows a thing or two about audio and proper adjustments.

Lost track of the number of times I've seen where a simple, PROPER audio alignment sequence has cured lots of audio problems - and proper means using test equipment that's located outboard of the ears. TIMS, deviation meter, things like that.

.............Wished I was there to see the radio managers face when he got the message that the FCC was waiting for him downstairs! The major issue is we requested he shut the unit off early on in the troubleshooting (weeks ago), but he would just say "It is not us!" and hang up the phone. All of the equipment connected to his console sounds very poor on tx and his dispatchers are always telling people that they cannot be understood on the radio. Oh well. Same poop, different toliet..........FatBoy.

[FatBoy]

I freely admit that I would like to learn more of the technical info behind how to properly align the audio in these systems. That being said, what I have been taught and picked up on my own has seemed to work better than most at this point. Just being ok with that fact goes against my continuing improvement goals, but am unsure where to go to learn it (can anyone point me in the right direction?). I did find out that said offending radio manager maintains his own stuff (IE, does not use an outside shop). I was on a conf call with some high level county radio system managers and the state EMS radio manager people and was told this guy makes everything hard ( read that as he is scarred of anthing that is not 110w VHF). He has VHF simplex patches to all of the radio systems he needs to use (every other facility has several EDACS/Moto trunked control stations AND the UHF MED radios for direct communication). I am beginning to think he might use some sort of horse-crap Critical RF ghetto console or something. Really starting to make sense why his dispatchers have such a hard time communicationg. FatBoy.

[Bill_G]

Unfortunately, in this biz you don't get to learn about something until it's in front of you. Then you're supposed to be an expert. Already. You do the best you can. Keep notes. Keep site books, or customer logs, or something you can refer to in the future cuz after a while you will develope CRS (can't remember stuff). All anyone can ask of you is when you rub two brain cells together that you can get some heat. Work the problem, and dog it out. I think you did good. Interesting problem for sure.

As for learning stuff, God bless the web, and all the people in it. Work on your Google-Fu. Don't be afraid of asking questions. Don't be afraid of reading books. RTFM. Take pride in your work, but don't invest your pride. Have the courage to be wrong. You're only human. You're out there pretty much on your own. Get your people skills going. Learn how to maintain customer confidence. Put everything you got into learning something fast. And then you get to move on to the next job with all the challenges it has. They don't teach this in school.

Take some sympathy on that hospital comms guy. It sounds like he hasn't learned how to not invest his pride, and probably hasn't found the courage to be wrong yet. Those are two gigantic steps for a lot of techs. The first thing you learn is self confidence which means finding the courage to be right. You learn how to be decisive, how to split a problem, take a direction, and then fix it. But, sometimes the problem fixes you. You have to take a step back, look at your assumptions, probably retrace your steps, and sometimes eat a little crow. Nothing wrong with that. It's part of growing up.

Take care, and above all, have fun. Enjoy this. This work is a blast. You get to drive in the country, walk through buildings, climb up roofs, build towers, put holes in walls, put in wiring that looks like plumbing, wrench on millions of dollars of equipment you cannot even begin to fully understand, and get people talking. And you get paid for it!!!! Bonus!

Enjoy!

[FatBoy]

wow, the above post is a great summary. Thank you guys for your hard work. Anyone in North Florida following this thread? Trying to do some networking up there and am just starting to make in-roads. Thank you, FatBoy.