Batboard

I have just finish adjusting the audio on my Spectra-tac voting system and I am still getting an ocassional chrip in the audio especially on weak signals. I've followed the book for the adjustments and the repeated audio sounds good. The following is a breakdown of the adjustments and equipment.
3 spectra receivers
3 spectra tac encoder boards adjusted for 2175
3 Squims audio input adjusted for 0db with a 1kc signal at 5kc devation and then the status tones were adjusted for -13dbm
1 command module & tone keying module: the command module adjusted for 0db with a 1kc signal at 5kc devation
The repeater in this system is a Micor UHF repeater with a unified chassis.
I am using Spectra-tac equalization boards with each receiver.
These checks were done with calibrated service monitor.
All the jumpers in the equipment have been check for -13db operation.
All this equipment is co-located at the receiver site. (no phone lines)

I'd just like to see if I've missed something in the adjustment phase that mabe causing the ocassional tone to show up the repeated audio signal.
Thanks for your help and advice in advance

Why are three receivers at the same site?

If everything is colocated, then you should set things for -10db or so, not 0db. 0 is too loud. This stuff was expecting you to drive a phone line with 0db, and have it arrive at the other end around -13db. Reading your procedure, you gave yourself a little headroom by adjusting at 5kc dev instead of 3kc.

With colocated equipment, or lossless system like a microwave, I set receivers to send -10db with 1k tone dev at 3khz. That puts the 2175 status tone around -23db. You can't really set the -13db relationship in the receivers since it is a fixed level in each line driver. It is what it is. But, they are generally pretty close to that. I set the SQM inputs for -23db status tone, and I set the line out to the transmitter for -10db 1khz tone. Disable each SQM and verify each will produce -10db 1khz tone enabling one SQM at a time. It should be good to go.

Hi Bill
Thanks for the reply. This is a low band split site repeater system with remote receivers. The link receivers are at the main receiver site to elimate the need for phone lines. There are two lowband receivers (same frequency) on two different antennas at different hights at this site. The third receiver at this site is a uhf link by RF to a totally seperate lowban receiver site.
In setting the audio/status tone I used the Spectra Tac manual to make these adjustments. So let me make sure I understand your procedure
Step 1: set the input freq to the receiver using 1kc tone at a dev of 3khz instad of 5kc and set the line out of each squim to -10db instead of 0db.
Step 2: set the 2175 status tone for each squim to -23db instead of 13db
Step 3: set comparitor line out to -10 instead of 0db
Now just a simple question, in setting your 1kc tone at a dev of 3khz this does or does not include PL? the way I did it was to set the PL tone to .500kc and then set 1kc tone to 4.5KC devation for the full 5kc of devation.
Thanks again I will try this after I see your reply
Mike

ABANAKA wrote:Hi Bill
Thanks for the reply. This is a low band split site repeater system with remote receivers. The link receivers are at the main receiver site to elimate the need for phone lines. There are two lowband receivers (same frequency) on two different antennas at different hights at this site. The third receiver at this site is a uhf link by RF to a totally seperate lowban receiver site.

Interesting setup. Why two receivers on two antennas at the same site? That could get confusing for a comparator if their line equalization is slightly different. It would bounce back and forth causing weirdness. Diversity receive is generally done at the rf level, not the audio level.

In setting the audio/status tone I used the Spectra Tac manual to make these adjustments. So let me make sure I understand your procedure
Step 1: set the input freq to the receiver using 1kc tone at a dev of 3khz instad of 5kc and set the line out of each squim to -10db instead of 0db.

You are correct about how I set the tone. I seem to recall the Motorola manual using full deviation for alignment, but that assumes all users radio hit full deviation. Usually people end up with 50% deviation averages. There are some boomers with hot mics and good technique, but most people talk fairly quietly and barely exceed 2khz. So, I set my levels lower while leaving some headroom for the loud guys. it comes out sounding more natural.

The "squim" is located in the comparator. The SQM (signal quality module) is not in the individual receivers. It is the termination of the phone line to the remote site, and contains the logic and audio processing that makes the voter work. The receivers have a 2175 status tone generator card (encoder) and a line driver card. You adjust the line out of the receiver for -10db with a 3khz dev tone input.

What I don't recall right now is if the SQM's have an input adjustment pot or not. It's been a while since I touched a SpectraTAC. All the ones I maintained have been replaced with DigiTACS and JPS SNV12 voters. I don't have a manual at home, and of course I can't find one on line to look at right now. I seem to recall a measurement point on the front of the SQM, a tiny phono jack, but I can't remember if there is a pot I set to rough in all the phone lines from the remote sites. During PMs and when I was fixing a problem, I used to jack into each module, and if I didn't see -20db or so of status tone, I chased it down.

Step 2: set the 2175 status tone for each squim to -23db instead of 13db

That should happen naturally since the -13db relationship is built into the receiver by the status tone encoder jumper set for -13db. Status tone is sent to the line driver card, and should hit the phone line 13db down from where the receive level was set. Since we're setting receive level for -10db, the status tone should be around -23db or so.

Step 3: set comparitor line out to -10 instead of 0db

Yes - for the same reasons. Since everything is colocated and you have no telco phone line loss, you can overdrive the transmitter input with 0db input. You want the input to be around -10db. So, you set the line out for -10db. You don't hit the transmitter as hard, and it sounds more natural over the air.

Now just a simple question, in setting your 1kc tone at a dev of 3khz this does or does not include PL? the way I did it was to set the PL tone to .500kc and then set 1kc tone to 4.5KC devation for the full 5kc of devation.

Set up your service monitor to generate 1khz tone at 3khz dev. If you are using 500hz of PL, then the total dev would be 3.5khz.

When you say "Chirp", what exactly do you mean? You'll always get a slight "click" or "cheep" when the comparator votes a different site mid-transmission. It's impossible to get rid of completely if you're using a status tone based voting system.

Is the Notch Filter switch on the comparator enabled or disabled? If the notch filter is disabled, you get more of a beep than a click.

d119 wrote:When you say "Chirp", what exactly do you mean? You'll always get a slight "click" or "cheep" when the comparator votes a different site mid-transmission. It's impossible to get rid of completely if you're using a status tone based voting system.

Is the Notch Filter switch on the comparator enabled or disabled? If the notch filter is disabled, you get more of a beep than a click.

I also wondered if he meant the normal "creaking" sound SpectraTACs made when switching, or if he meant the momentary bee-doop that bleeds through upon keyup. But, with his levels set so high, it's hard to say. And he might be up against dried out caps on his SQM cards.

Found a manual in my office. It confirmed what I couldn't recall - there are monitor points, but no adjustment for the SQM input. It is what it is. My notes show how I tried to SP some additional gain and adjustment, but I know I never took it very far. Either the phone company gave me what I needed, or I tried to shove more down the line from the receiver to compensate.

The tones that I am hearing on occasion is durning transmissions while people are talking, I don't beleive its switching sites when this is happening. With the information that you all have provided I beleive I will try resetting the levels to -10 instead of the 0db level with a 3.5kc (.5kc Pl) Devation. I will confirm the -23db Status level. I will come back and confirm my finding this weekend.
Thanks for everyones input

Bill_G wrote: Interesting setup. Why two receivers on two antennas at the same site? That could get confusing for a comparator if their line equalization is slightly different. It would bounce back and forth causing weirdness. Diversity receive is generally done at the rf level, not the audio level.

What do you mean? Is diversity switched by RSSI? How does one determine which receiver to use for the link? I'm asking because I'm curious, and I know that diversity has been used by AT&T Long Lines. I just have trouble following as to why one would switch receivers based on some other criteria when noise is already being analyzed in the voter system. Sure, KISS.

I suppose it makes sense and works for FM where you're looking for a solid signal or carrier that is either there or not.

SlimBob wrote:

Bill_G wrote: Interesting setup. Why two receivers on two antennas at the same site? That could get confusing for a comparator if their line equalization is slightly different. It would bounce back and forth causing weirdness. Diversity receive is generally done at the rf level, not the audio level.

What do you mean? Is diversity switched by RSSI? How does one determine which receiver to use for the link? I'm asking because I'm curious, and I know that diversity has been used by AT&T Long Lines. I just have trouble following as to why one would switch receivers based on some other criteria when noise is already being analyzed in the voter system. Sure, KISS.

I suppose it makes sense and works for FM where you're looking for a solid signal or carrier that is either there or not.

I believe it is a combination of RSSI and the percentage of correction applied to the recovered payload, but I'm not really qualified to discuss antenna diversity systems and the criteria they use to improve reliability. We've put them in. We've seen them work and not work. Generally, it is used on frequencies above UHF (450mhz), but I have seen it used in VHF DF (direction finding) equipment. I don't know how well spatial diversity would work for low band. It is commonly applied in microwave links where atmospherics are expected to diffract the beam. But, it has been used in some cellular systems to overcome inbound subscriber fade. Lately, MIMO seems to be the direction that industry is going. In this case, I suspect Abanaka will not experience any benefit.

Remember that the SQMs, both old and new versions, also have a center frequency adjustment...........