When learning the radio trade some years ago as a low paid button pusher for a 5,000 watt religious station, I noticed a few of our preacher's shows were piped in live via an "equalized phone line". The audio quality was relatively good compared to a standard phone line. My questions: was this the correct terminology? Are these such dedicated phone lives still in use? And, what sort of technology went into making these lines sound as good as they did?
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Equalized Phone Line
- Thread starter jimoneal
- Start date
It "could" be done today, but there's probably not a phone system left anywhere that would easily permit
a REAL copper pair from here to there.
What was done basically was to test the response of the line. After learning how much the line
rolls off high frequencies, equalization is added to loss down the frequencies that get through easily.
Then by comparision, the higher frequencies aren't attenutated as much.
I think any amplification or gain was the responsibility of the end user.
Today, I'd think you could do as well with fairly cheap equalizers and a regular phone line.
But I still don't think there's any way to lease an actual true copper circuit anymore.
Pretty sure you gotta go through the switch.
a REAL copper pair from here to there.
What was done basically was to test the response of the line. After learning how much the line
rolls off high frequencies, equalization is added to loss down the frequencies that get through easily.
Then by comparision, the higher frequencies aren't attenutated as much.
I think any amplification or gain was the responsibility of the end user.
Today, I'd think you could do as well with fairly cheap equalizers and a regular phone line.
But I still don't think there's any way to lease an actual true copper circuit anymore.
Pretty sure you gotta go through the switch.
The fly in the ointment is what the phone company calls 'Loading Coils'. You'll see them on or between poles...they tend to be round, maybe 6" in diameter by 18" long. Their role in phone company life is to kill off everything not within the 300hz to 3000hz range used for dial up service. So even if you do manage to get a bare pair of copper wires from point A to B, you need to make sure they are 'unloaded' in order to be able to EQ them yourself. An Indiana station did get a bare, unloaded pair (I think it was called an Alarm Circuit, but don't hold me to that) about 5 years ago. Passes audio in either direction and at the 3 mile distance, a stereo Behringer rack mounted EQ with the two sections series strung provided plenty of flexibility to get the line flat well beyond 10khz. Station uses it to bring a Marti receiver from the xmtr site back to the studio. Not sure if that can be done in 2010, but AT&T did it in the mid 2000's. It helped to have the circuit number of another nearby station's 'bare pair'...that led Ma Bell right to what I was asking for.
Many years ago, we used equalized phone lines for our program circuits. They were equalized to 15kHz. That was before the phone company put loading coils on all of their circuits. Today, you're better off using the internet and mp3 (or other) encoding.
Wouldn't they have had to have done something about the loading coils to get this DSL to work over a copper pair?
There's quite a hash in the phone line, but none after 4 or 5 series audio filters upstream of the actual phones.
Sounds like there's gotta be some widband there. They must be picking off a Uverse box before any real distance
or loading coils.
There's quite a hash in the phone line, but none after 4 or 5 series audio filters upstream of the actual phones.
Sounds like there's gotta be some widband there. They must be picking off a Uverse box before any real distance
or loading coils.
They had to have unloaded the pairs that are DSL capable. The trick would probably be finding unloaded pairs that are not dedicated to DSL/Dial Up service. In the past, unloading the pair was part of the 'construction' cost which varied wildly depending on whether or not there were unloaded pairs already in place. Many years ago, it seems that in Indianapolis, the cost to set up a 15khz line was up to $700 if the unloaded pair was already in place. About that time, ISDN came along & I suspect that a person would be greeted with laughter (or silence) if they ordered a new EQ'd circuit today. I do have one station in my stable that is using an EQ'd stereo pair, but it's been in place since the early 90's when they were still commonplace. Most of it goes over Fiber now, but the ends are both analog. Not sure what the guy is paying, but I priced an STL for him and he seemed to think that for what he's paying per month, he likes the fact that the maintenance of the lines are someone else's problem. One less event to ring my phone...
Tom Wells said:
You have hit the nail square on the head. A few years ago we wanted to transport audio from a cable TV studio to a cable radio station some 30 to 40 miles away. We could not get a true copper pair and thus could get no better than phone line quality audio no matter how we EQed it. The technique now is that at the CO they usually digitize the signal and then it is transported over their system along with all of the other stuff until the end closest to the other subscriber where it gets converted back to analog for the last mile so to speak.
Loading coils have all but vanished, due to DSL as several have stated above. You might find them still in some very rural areas where they couldn't provide DSL anyway. With more deployment of fiber cables the copper pair will soon be an endangered species even to your local CO. Also we will lose the security of the Central Office Battery supplying the necessary voltage to keep the phone on even during local power outages. Cell phones may become the only fail safe option for emergencies, or rather as fail safe as you can expect.
There's still a tariff most places for equalized service at the 5 and 15KHz levels, and I bet you can find the tariff for a stereo pair (Different from 2 eq'd lines. I ckt # with A and B loops). What's now provided is analog only over the last mile at each end, it's digitized and shclepped along the system using as many bonded 64 Kbit circuits as necessary. Loading coils were used to extend the usefukl range of a copper pair - but the tradeoff was twofold. You lost DC continuity,and everything over 3KHz went rapidly away. Steve Church of Telos fame, along with some of his employees, probably is the best fount of analog telco knowledge out there. Also some of the old heads at Comrex.
As copper went away, countless REP-111 Western Electric repeat coils were abandoned in place. Scarf up every one of there you can find. They have many uses in isolation and matching in the broadcast plant. Properly terminated, they'll even pass baseband to your exciter. Cruise the wire room in your facility, and if someone like me hasn't already bagged them, you should find several.
As copper went away, countless REP-111 Western Electric repeat coils were abandoned in place. Scarf up every one of there you can find. They have many uses in isolation and matching in the broadcast plant. Properly terminated, they'll even pass baseband to your exciter. Cruise the wire room in your facility, and if someone like me hasn't already bagged them, you should find several.
I remember years ago when a low-power high school FM station was using a "communications grade" telco line as its STL. The audio was barely good for 8 kHz, and of course strictly monaural. It was like listening to an AM radio on the FM band.
These days, I believe standard laneline telephone circuits are digitized at 8000 Hz, so in areas where everything's fiber optic (except the "last mile"), you'll never get better than about 3.5 kHz audio response (4 kHz is the theoretical maximum, minus a bit for anti-aliasing filters).
These days, I believe standard laneline telephone circuits are digitized at 8000 Hz, so in areas where everything's fiber optic (except the "last mile"), you'll never get better than about 3.5 kHz audio response (4 kHz is the theoretical maximum, minus a bit for anti-aliasing filters).
littlejohn said:
I think that you may be confusing loading coils and isolation coils (transformers). Loading coils were just inductance coils placed in the lines to offset the capacitance which naturally occurred with a pair of wires going any appreciable distance. Isolation coils were used to keep any currents in local equipment off the outside loop. Generally they were located at the wire entry point to a facility. In the old days only equipment furnished by Ma Bell could be directly connected to the telephone line. Anything else had to have an isolator furnished also by Ma Bell.
ATT(SBC) in Oklahoma will provide "equalized radio loops" that are Aptex cards on both ends that take your analog audio and covert them to digital, push that down the line, then convert it back to analog. It works great for them because it's all digital so they don't have to deal with the all copper issue. They are reliable and sound good, with no appriciable delay. Several stations around town here are using them for Marti pickups and even STLs. In some areas ATT (SBC) will still provide alarm loops. That's a true copper path in which they jumper things directly at the switch. So distance-wise it goes through the CO but is hard-wired to bypass the switch itself.
Thanks for refreshing my memory after so many years on the difference between the loaded and un-loaded lines. The "Dry Pair". I had forgotten which was which. That confirms a method an old radio friend of mine told me to "weld" the splices down the length of the lines by charging up a large electrolytic capacitor...shorting one end of the line and smacking the other end of the line with the charged capacitor. As I remember, the DC resistance of the lines got lower after a few arc welds and the balance (thus cross talk and noise) got lower. It has been many years. I did this periodically as a preventative maintenance measure every 6 months or so during a 3am Monday morning checkup. I had a nice 20uf oil filled cap that was charged to 400volts. Even with the copper resistance over 3 miles a nice arc would form when the clip lead touched to the wire. I zapped the lines until the resistance did not drop much more.
20-15kc +/- 1.5 dB was not a problem when the lines were working correctly. Stereo separation was as good as the stereo generator would allow for the time. It was easy to see using pink noise how much phase shift there was on both ends of the spectrum. STLs weren't great at that time as they had noise and distortion from the modulation/demodulation transfer function so good phone lines sounded pretty good to my ears.
20-15kc +/- 1.5 dB was not a problem when the lines were working correctly. Stereo separation was as good as the stereo generator would allow for the time. It was easy to see using pink noise how much phase shift there was on both ends of the spectrum. STLs weren't great at that time as they had noise and distortion from the modulation/demodulation transfer function so good phone lines sounded pretty good to my ears.
Also, a side note about the loading coils... The reason they have loading coils is to increase the audio to service that is a long ways away from the CO or telephone company equipment (customers on long copper lines). With DSL and other digital services, they have to remove them as others have stated. the problem some times is that the audio drops to an unacceptable level when they do this.
B
bilco
Guest
8 Khz and 15 Khz are theorietically still available. I use two 8 Khz lines to feed two of my AM's here in Las Vegas. They have been in place since 2001 and work fine. In reality, I feed a signal in and get a signal out and the signal is transported by methods that are transparent to me. I know they leave the premeises equipment here in digital fashion, and arrive at the transmitter site in analog fashion. I also have an 8 Khz line from a hotel's roof top for an RPU receive signal that leaves there analog and arrives here analog. No idea what happens in between but it passes my proof so who cares. Of course that's 6 miles straight down Flamingo rd. Now days, the telco has few people who understnad what an EQ'd line really is all about. By the way we use the 8 Khz lines for our AM's after comparing the listener results using 15 Khz on one station and 8 on the other. No-one could tell the difference since most AM radios today are lucky to pass over 3 Khz. Some others have put their own equalizers in plce, I let the telco do it for me.
I spent lots of time listening to our equalized phone lines "back in the day" looking for any frequency roll off. I just remembered an old Bell Telco Central office guy telling me he got my equalized pair "flatter than a platter of piss."
The 111C transformers (grey, oval shaped, about 6 inches high) are worth about $100 on the used market. Grab them if you find them!
We have two pair mounted on rack panels in our rack room--they're on the program lines for our two FM's. Even though the lines only go about 30 feet out of the studio building underground to the adjacent transmitter building, we've had lightning (actually the em pulse from a strike) take out the IC amps in the consoles (Auditronics 2500).
The 111C transformers are very flat, have no noticeable phase shift, and provide the needed isolation between the "transformer-less" IC output amps and the "long" line to the audio processors in the transmitter building.
Back to the original topic: As noted, few telephone lines are "loaded" anymore--this vanished back in the days of dial-up modems. If you have a remote pots line in the same central office (e.g.--exchange) as the studio you can equalize this line on the studio end, and it will repeat every time you use the line. This works because you will get the same path from remote phone to central office, then from central office to the studio, since it is the same pair of copper wires each time.
Unless they've digitized one or both ends to get more lines over a pair, then this trick won't work. Still, even long distance, the low end is not cut off as much as it used to be, so a cheap equalizer can make a dial-up feed sound respectable. I use the ART equalizers, run about $100 or so, for this purpose, have six I use on incoming phone lines as well as Marti feeds (to cut off that irritating hiss around 6 KC).
We have two pair mounted on rack panels in our rack room--they're on the program lines for our two FM's. Even though the lines only go about 30 feet out of the studio building underground to the adjacent transmitter building, we've had lightning (actually the em pulse from a strike) take out the IC amps in the consoles (Auditronics 2500).
The 111C transformers are very flat, have no noticeable phase shift, and provide the needed isolation between the "transformer-less" IC output amps and the "long" line to the audio processors in the transmitter building.
Back to the original topic: As noted, few telephone lines are "loaded" anymore--this vanished back in the days of dial-up modems. If you have a remote pots line in the same central office (e.g.--exchange) as the studio you can equalize this line on the studio end, and it will repeat every time you use the line. This works because you will get the same path from remote phone to central office, then from central office to the studio, since it is the same pair of copper wires each time.
Unless they've digitized one or both ends to get more lines over a pair, then this trick won't work. Still, even long distance, the low end is not cut off as much as it used to be, so a cheap equalizer can make a dial-up feed sound respectable. I use the ART equalizers, run about $100 or so, for this purpose, have six I use on incoming phone lines as well as Marti feeds (to cut off that irritating hiss around 6 KC).
nmore, I'm niot coinfusing them, they're two totally different things for different purposes, as you note. It's justt that when the lines are top - of - mind is a good time to go prospecting for abandoned REP-111s, which have value in the broadcast plant. I haven't tried to put AES3 through one, I wonder if you could peak it to pass.....
littlejohn said:
Gotcha, I reread your post. I had forgotten the term repeat-coils which the 111 series were. And as noted they did indeed have excellent response and though they were used for isolating the phone lines from the local equipment they are an excellent choice for other uses such as ground loop elimination and even connecting unbalanced consumer gear to balanced inputs. I got a bunch of them at one time from a friend with connections but over the years they and I drifted apart. Wish I still had them all.
Actually, the trend is for telcos to REMOVE loading coils today-because they make DSL impossible. That said, many telcos no longer do analog program lines. I know that in Los Angeles they have been doing digital program lines (using APT-X) for years. They use a 56 kbps point to point data line for 8 kHz and a 128 for 15kHz.
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