SpectraTAC and Phone Line High Frequency Roll Off

[Birken Vogt]

We recently inherited a system with lots of remote receivers linked back to a SpectraTAC and associated copper line problems.

I am looking for some experience with what amount of flatness in the frequency response of the telephone line is required for proper operation of the comparator. Right now the line in question has a high frequency roll off beginning somewhere around 2.2 KC and at 2.8 KC it is -13.7 dB relative to 1 KC. Low freq. is fine and the problem of course is that this site gets voted inappropriately when other sites are quieter.

The phone company's MO is to send a crew out to do some repair or other, then wait to see if we call back and complain. This means that each time they say maybe it is fixed, we have to sweep the line to see, so I am hoping to learn when we can say it is "good enough". Right now we are testing 400, 1k and 2.8k but does the SpectraTAC benefit from anything over 3k? How high should we go, or expect it to go?

[N4DES]

Look on the audio control cards for the audio tailoring jumpers and you can use those to make, if I remember correctly, 3, 6, and 9 db adjustments to the audio.
But I must warn you that it will also change the 2175 status tone and it needs to remain untouched after you select your jumper setting.

[d119]

Considering that telco lines are specified for 300-3000Hz (usually), I doubt the Spectratac is looking at anything over 3000Hz.

But the high end, as you know, is the most critical, so you are on the right track.

I'm surprised the telco has such issues with the circuits. You should be able to compensate for this to some degree, as KS4VT has indicated. What kind of receivers are they?

[Bill_G]

If you don't have a manual, there is an older one available at Repeater Builder.

D119 is correct. Phone lines are generally cut for 300 to 3K. The SQM has a high pass cut for 2khz used to determine the noise floor for voting.

Be aware, because of their age, you may be up against dried electrolytic caps causing poor performance rather than a telco issue.

[Birken Vogt]

The receivers are MTR2000s. We can compensate for the phone lines to some degree using the eq feature. I would just rather make the telco do their job; after all, that is why we pay them. Besides if I eq a bad line today it may get worse tomorrow.

We found this roll off measuring the line end-to-end and the telco told us the same thing, they just have not fixed it yet.

SQMs have been swapped, etc. before I was on the case to try and fix it internally but the line measures out pretty bad.