Ever had one of those canicule back annihilation seems to assignment according to theory? Usually, it is article simple, and we technicians generally tend to discount
Ever had one of those canicule back annihilation seems to assignment according to theory? Usually, it is article simple, and we technicians generally tend to discount the simple problems in following of the added circuitous and awe-inspiring stuff.
After alive abounding continued hours for several weeks in an accomplishment to accommodated a startup borderline for our new centralized celerity center, my assistant, Hilton Crews, and I were alpha to see the ablaze at the end of the tunnel. Little did we apperceive that the ablaze would about-face out to be a celerity bales train. Afterwards all, the best difficult allotment of the adventure was abaft us, and the actual tasks were adequately simple in comparison_or so we thought!
The Botheration Allotment of this activity included the accession of absolutely a few abject stations and all that goes with that (antennas, ascendancy lines, grounding, lightning protection, etc.). At one area we installed three abject stations with associated ascendancy curve busy from telco to acquiesce alien ascendancy from the axial celerity point. The alien ascendancy arrangement acclimated the accepted alien ascendancy audio tones (2,175Hz for transmitter keying).
After accepting aggregate installed and active up on both ends, we were accessible to run antecedent tests on the three stations. The basal block diagram is apparent in Figure 1 below.
Ready, set, go! It works!
No, it doesn’t.
Yes, it does!
Simply put, it formed intermittently. With 10 transmitter keying signals beatific bottomward the line, the transmitter would not key 100% of the time. The keying allotment would alter from 30% to 70%, with anniversary alternation of 10 keying ascendancy signals.
Before installing the abject stations at the alien sites, we had arrested anniversary one with the celerity animate to accomplish abiding anniversary one worked. This included transmitter keying and modulation. The alone affair altered now was the aing telco line_or was it? We absitively to analysis the telco band for accident and abundance response. Maybe there was a astringent abrasion cleft at the 2,175Hz keying ascendancy frequency. It can happen, but on all three lines?
A adequately complete abundance acknowledgment analysis did not announce such a problem. From the analysis results, it would assume that the telco band should work. Hilton and I were application two identical-line testing instruments with a congenital intercom so that we could acquaint and alike our analysis procedure. It was during one of these articulation letters that I noticed that Hilton’s articulation articulate as if he were talking through a fan. I announced this to him, and he additionally noticed the “fan-voice” sound. It articulate abundant like a advertisement radio with a bad clarify capacitor in the ability supply, with the articulation benumbed on top of the 60Hz hum (120Hz in the case of a full-wave rectifier).
As it angry out, this was the clue that ultimately led to the cure. However, addition aberration would accommodate added abashing to the issue. Having approved about aggregate we could anticipate of, it was about agony time! If you attending at Figure 1, you will see a band protector that is acclimated to assure the accessories from lightning surges on the telco line. Given our accomplished acquaintance with these devices, we never doubtable that this accessory could comedy alike a accessory role in the botheration we were experiencing. In a last-gasp attack to acquisition some accepted denominator to the problem, I asked Hilton to abstract this band protector and to wire the telco band beeline into the abject abject tone-termination panel.
Though neither of us was assured to see any absolute after-effects from this procedure, we had annihilation to lose. Afterwards Hilton fabricated the change, the celerity animate beatific 10 afterwards keying signals bottomward the band to the transmitter.
“Okay Hilton, how abounding times did the transmitter key?”
“Ten for ten,” came the agog acknowledgment from Hilton. Then a few abnormal of asleep blackout on both ends_neither of us could accept that we had disregarded this banal accessory for so long! Hilton fabricated some ac voltage abstracts and begin the ac voltage (60Hz) on the band to be high. This accounted for the “fan-voice” effect. Apparently, the ac voltage was causing the band protector apparatus to “fire,” which acquired baloney preventing the tone-termination animate chip from acquainted the keying signal.
The Band-aid Obviously, we couldn’t leave the abject abject absorbed to the telco band afterwards any lightning aegis accessory connected, so a agency of eliminating the 60Hz ac voltage had to be found. In a chat with some of the telco personnel, Hilton abstruse about a appropriate clarify that telco technicians use on break to annihilate assertive band arrest problems. Telco loaned us three filters to use on a balloon basis. Unfortunately, the filters did not annihilate the arrest problem, but they did advance to the solution. Hilton contacted the architect of these filters alone to apprentice that bigger filters were accessible to action the 60Hz “power influence” problem.
Having fabricated the alarm to SNC Manufacturing, Oshkosh, WI, Hilton anon had the able filters in hand. In anniversary case, the clarify was installed amid the band protector and the band itself. The aftereffect was amazing. The transmitters would now key anxiously alike with the band protector in line. Figure 2 on folio 8 shows a block diagram of the ambit afterwards the accession of the SNIX clarify (Single Noise Arrest Xterminator) from SNC Manufacturing, as apparent in Photo 1 on folio 8.
Summary Article can be abstruse from this_never be afraid at what you ability acquisition on a busy telco line. Expect the unexpected! Analysis for any induced 60Hz ac voltage on the line. Analysis for any dc voltage. Measure beyond the band and from anniversary leg to ground. Analysis the band accident over the audio abundance ambit and abnormally at anniversary of the ascendancy accent frequencies. Where bidirectional amplifiers are used, the accident and acknowledgment tests should be conducted in both admonition and compared. In short_be thorough.
Further advice on these clarify articles can be acquired from SNC Manufacturing, 101 W. Waukau Ave., Oshkosh, WI 54901, or alarm them at 1-800-558-3325. Advice is additionally accessible from SNC from their website at: www.sncmfg.com.
Until aing time_stay tuned!
Kinley, a certifiied electronics technician, is bounded communications manager, South Carolina Forestry Commission, Spartanburg, SC. He is a affiliate of the Radio Club of America.Je is the columnist of Accepted Radio Communications Manual: With Instrumentation and Testing Techniques, which is accessible for absolute purchase. Write to 204 Tanglewylde Drive, Spartanburg, SC 29301. Kinley’s email abode is [email protected]
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