Wireless UHF link for voter

[efc]

Hello,

Anyone have experience with a wireless UHF link for the JPS SNV12 voter and level sets?Got mine in a system,VHF,CM300 for tx link,CM300 for rx,JPS PTG 10 for status tone.Cannot get system to vote quite right.Audio sounds hollow,like thete is not good audio response.Set the tx end to narrow band modulation,and set the rx end to pass 1k at 0 db,status tone at -7.0db.Any input would help,thanks.

Thanks

[Bill_G]

What is JPS PTG 10? Is that a stand alone pilot tone generator? Might not be necessary since your using a radio link. When the far end receives, it keys the link transmitter which, in turn, raises the COR line on the near end receiver (or goes low depending on how it's configured). You could have used that instead of status tone.

I think you need to lower your levels a bit. Generally voters are looking for a maximum -10db input with the status tone another 13db below that. That kind of dynamic range is hard to achieve in a link which is another reason to use COR detect.

The main problem with using radio links to return receive audio is they have to be super quiet, or the voter will be voting on the link receiver noise, not the far end receiver noise. That's problem #1. Problem #2 is the link might not pass enough high frequency noise from the far receiver to properly vote. ie: the far end link transmitter will roll off the high freq content above 4Khz that the voter likes to work with. There are equalization settings in the SVM modules you can apply. You'll probably have to max them out on the linked SVM module to get enough noise for the voter to work with. Likewise, you'll have to apply the opposite curve to the local receiver to roll off some of the high freq content, or it will never get voted - it will always be too noisy compared to the linked receiver. You might have to do that with a simple RC (resistor and cap) across the local input to kill some noise above 4khz.

[kb4mdz]

While we're on the subject of RF linking for Sat. RX backhaul, anyone have any other pointers?

I'm in a situation where I'd like to do this for a channel, UHF for the main operating freq. so at first blush I'm thinking of going with VHF, but directional antennae at VHF are pretty large. Since the operating pair is in 452MHz/ 457 mhz, I might have enough isolation using the high 460's region. Or could I find something in 900 mhz? And how would I find such a freq? My regular friendly neighborhood freq. coordinator?

Thanks,

[Bill_G]

If your rptr pair are 452/457, you could get away with a link in the 460's if you use a pass/reject duplexer on your rptr. If you use a reject only, you'll clobber yourself.

[efc]

Thank you,I copyy everything you have said,and the voting process you have mentioned,i have thought of,i e,the high freq roll off,not really tried yet,due to time constraints.

Thanks,will reply further later,at Motorola school.

[Bill_G]

You're welcome. The signal-to-noise voting is used by MOT and JPS, but they were intended to be connected by high quality phone lines that had audio response to 4khz. Radios tend to roll off at 3khz. The s/n voters insert a high pass filter above 3khz knocking out the voice band. So, you have a radio link killing off audio above 3khz, a voter killing off audio below 3khz leaving very little to work with.

And that's if your rf link is fully quieted with no path or fade noise of it's own contributing.

It can be done, but you have to fiddle. It will not dial in right away.

[efc]

Thanks Bill,

Yes, I know about the rolloff,at least the SNV 12,saw that it votes above 2200hz,primarily where it "sees" noise.RF wise,with my R8000,I see-80 db with spectrum analyzer arriving at the receiver site.Yes the signal is a good level,but even at that,I hear and see a slight hiss which I know is noise creeping in.My thoughts were that that in itself will introduce a problem to the mix,in addition to the rolloff.Initially I got a call that units were "cutting" out,arrived on scene,and my suspicions were correct.The wireless sight was voting periodically,with audio dropping.The unit that called in was no where near the wireless site,so I knew it was being favored,probably because of the rolloff issue,not enough noise above 2200hz,so it thinks that it is a good site.I tried turning the audio up on front of voter,was not favored anymore,but I was afraid the level was now too high causing over mod.Could not get any units to go in area to do radio checks,they were all busy……..figures.So another tech has been working on this,because I have been at Motorola going through the MCC 7500 course,which has been fascinating,and quite a good learning experience.

Thanks

[efc]

By the by,what is ACIM?It sounds like it is some type of protocols for consoles.

Thanks

[Bill_G]

By the by,what is ACIM?It sounds like it is some type of protocols for consoles.

Thanks

ASTRO Console Interface Module

Interfaces the console to a DIU which in turn interfaces to an ASTRO base station. It establishes the secure data link. Essentially an expensive and complicated modem.

[efc]

Oh,got it,thanks.

[efc]

By the way Bill, the PTG10 stands for Pilot Tone Generator.Which obviously produces Pilot Tone for Voters.It is selectable from 1950,or 2175.I use 2175,and it comes stock setup as 1950.It also has a line adjust and Pilot adjust in the housing.

[dag]

I'm interested how the UHF link in this discussion worked out. I am probably going to go the same route with two different systems, both using SNV12 voter cards. These systems are simulcast using Harris channel banks with VF-25 modules having a bandwidth of 300-3000hz, I couldn't even get TX PL tones through them. If I run the satellite receiver(s) through the channel banks I'm sure all will be fine, but I am proposing they go straight to the voter site to reduce cost. So my concern is if there is something more I need to do to the link receivers before sending them to the SNV12 module.

One of the issues I did run into was poor audio quality. On the repeaters I turned off pre-emphasis and de-emphasis with good results.

[Bill_G]

I'm interested how the UHF link in this discussion worked out. I am probably going to go the same route with two different systems, both using SNV12 voter cards. These systems are simulcast using Harris channel banks with VF-25 modules having a bandwidth of 300-3000hz, I couldn't even get TX PL tones through them. If I run the satellite receiver(s) through the channel banks I'm sure all will be fine, but I am proposing they go straight to the voter site to reduce cost. So my concern is if there is something more I need to do to the link receivers before sending them to the SNV12 module.

One of the issues I did run into was poor audio quality. On the repeaters I turned off pre-emphasis and de-emphasis with good results.

What model receivers?

[efc]

Hi, I escapes me right now ,but,can you turn off the pre emphasis and de emphasis on CDM 1250 radios? I will have to double check in the software,I think you can,and therefore,maybe get rid of my issues.On the SNV 12 just yesterday,I added maximum line equalization not the UHF link site,still was favored,but not as much.The channel 2 voter does not seem to exhibit the problems,channel 1 and 2 ,has CDM 1250 radios at a common site.I guess it possible that i could have another noisy site,therefore this site is favored,but I think it is still the Sig to noise ratio being the problem.I am not sure if there is a good way to check audio response for all the sites ,other than 2 people,one with a telephone test set,the other ramping from 300 to 3000 Hz,watching for sudden frequency roll off.

Thanks

[efc]

Hello just as an update,I figured out my problem.The receivers again are MTR 3000,I went into the channel info and set the receiver mute rule to "standard mute /unmute" I found out what was happening was that the MTR would receive a low level signal,pin 4 of the j7 AUX connector would go low,but the would be no audio on pin 7 of the AUX connector,until you raised the sig generator,several db.Then you would have your audio.So.......when a mobile with a weak signal,because of distance,would hit the site ,you would have no audio.Then the audio would go in out,based on his signal strength due to him moving.So,here are the pins I used on back of the MTR 3000: PIN 4 = PL DETECT/CSQ DETECT
PIN 7 = AUDIO HIGH
PIN 9= GND

Those then went into the MIC connector of a CM 200,UHF radio.

[Bill_G]

What was the MTR pin 4 set for previously?

[efc]

You know Bill........I do not know.

Thanks