What stations have you heard oscillators still on close to a station that was off the air? Usually they are AM daytimers, but sometimes other AMs and FM oscillators and sometimes more powerful signals from FM exciters. Oscillators can be heard a few blocks, but the FM exciters can sometimes be heard for miles. Do any of you know if strict daytimers (no PSSAs and very limited PSAs, usually limited by Class As) are required to turn off oscillators at night?
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Oscillators On After Signoff
- Thread starter Schroedingers Cat
- Start date
I've wondered about this. For years (don't know if they STILL do it), but WKXO-1500 in Berea, KY has been clearly heard for about a mile, or so, around their tower well into the night...even as late as midnight when I've travelled through the area on I-75. They are supposedly a DAYTIMER according to what I can determine.... I've noticed this on NUMEROUS trips through the area.
PART-15 night service?????????
PART-15 night service?????????
Schroedingers Cat said:
I recall back in 1983, when putting WSRA-106.9 in Guayama, PR, on the air, we left the exciter on with audio being fed from the automation. The only way to the antenna was through the coupling to the final stage. We were able to carry the signal about 30 miles to the northern coastline of PR in the dense San Juan metro... with 10 watts!
The antenna was about 1000 meters AMSL, of course.
DavidEduardo said:
Must have been pretty good for passive coupling, and was that a measured 10 watts "leaking through", or was that a 10 watt exciter?
I'd think on a 10 watt exciter, only 2 watts might just walk through by passive coupling.....
In part 15 AM design, I have noticed is important to minimize radiation from the (unmodulated) rf osc which diminishes the result as
received in near field. If it's strong enough it diminishes the audio density and maximum loudness.
You wouldn't notice if the signal were over a watt, but at 100mw, leakage from the umodulated rf must be minimized.
I THINK I have heard many AMs still "partly on" over the years and much travel.
Often while driving at night, I'd find clear dead air on the AM which only seemed to provide quieting in a small area.
I think some of them stayed on all night at a pre/post sunrise authoriazation level, with no audio.
Many years ago, I was with a class C FM that had a failure in the PA tube socket. TPO was zero on meter with zero plate current. Plate volts were high as it did not shut down due to no overloads. Grounded grid final was coupling driver output to antenna. Phone call from sales rep 60 miles away about the fuzzy signal. Doesn't take a lot of watts with a tall antenna. Repaired tube socket and everything returned to normal. CSI 20 kW rig.
I remember when WTRX was doing some extensive repairs on their DA system back in the early 1970s, replacing the ground system, the transmission lines, ATU components, and phasor components. I lived three miles away, and right before they kicked the new system back on, there was a MODULATED signal from WTRX that was the about the same signal strength on the tuning meter as WKNR (1310 Dearborn) and WILS, which were probably in the 250-500 uV/m range. I remember figuring out what the power would have been if it were omni, and it seems it was somewhere in the 100 milliwatt range. I always wondered what they could have been running when that happened. There is a null in the night pattern near that direction, but it is not supposed to be a zero theoretical null. It occurred to me that it could have been near zero in the proofing and adjustment of the array, but the signal strength on day or night pattern had never been anywhere near that low at any time before that. There were always reradiating structures that threw the pattern off, and there is augmentation in that direction.
I called the station but just got the DJ, who just said that they had replaced everything but he had no idea what exactly they were doing. The engineers were "unavailable".
I called the station but just got the DJ, who just said that they had replaced everything but he had no idea what exactly they were doing. The engineers were "unavailable".
If the AM transmitter is off and the oscillator is on, all you'll hear is an unmodulated carrier as the modulation occurs at or near the final stage. Never will the AM oscillator be modulated. If you hear audio on AM, there's something more than the oscillator at work.
40 years ago, an already ancient 1KW Gates FM transmitter's filaments stayed on all night at WOXR 97.7 Oxford, OH. I lived better than 20 air miles from the site and heard it fine with an outdoor yagi.
40 years ago, an already ancient 1KW Gates FM transmitter's filaments stayed on all night at WOXR 97.7 Oxford, OH. I lived better than 20 air miles from the site and heard it fine with an outdoor yagi.
The RF generator makes sense. What is the range of power output you could get from that? Could you feed regular AF programming into it, or is it pretty much just test tones? Does a General Radio Impedance Bridge have that capability? The one I used in Physics had at least an AF tone generator, but I don't recall using RF frequencies, just AF to find L and C values of an unknown capacitor and inductor. It was a fun lab. The Professor was flabbergasted when he asked me in the oral final what I would use for a frequency standard and I mentioned WWV. Possibly the generator was separate from the Impedance Bridge. Guess I could look in the manual online.
cyberdad said:
Not with WKXO...They were running automated programming LATE at night. For many years, WKXO was linked up to WEKY-1340 in Richmond, KY and WIRV-1550 in Irvine, KY forming a 3-station network all with the same programming. In more recent times, WKXO-1500 has been running automated gospel music on its own -- for the most part. Their "night" signal was weak, but could be clearly heard for about a mile around the tower site. If you ever drive along I-75 at night, check it out as you pass Berea, KY. I've heard it EVERYTIME I've gone through there at night for the last several years. Their night power is listed as 0 watts!!!
Some solid state AM transmitters (BE comes to mind) continue to run their exciter after the power amps are turned off. With the BE-A series, this can cause a problem for daytimers since RF drive is still being applied to the input coupling of the power amps, but no fans are running to dissipate the heat. As a result, the small coupling toroids tend to unsolder themselves from the PA mother board. I know of at least one station that avoids this problem, by simply muting the PWM at sign off and then removing the mute at sign on. The fans still run, the unit stays cool, but no RF is sent to the tower.
I remember ads for one solid state AM transmitter manufacturer claiming that when their transmitters shut down, it was a complete shutdown to avoid the problem of a tiny amount of RF being passed to the tower. The manufacturer might have been Armstrong or Energy-Onix.
I remember ads for one solid state AM transmitter manufacturer claiming that when their transmitters shut down, it was a complete shutdown to avoid the problem of a tiny amount of RF being passed to the tower. The manufacturer might have been Armstrong or Energy-Onix.
Hello Schroedingers cat. If you heard programming, probably something else was going on. I made a career change a long time ago. Back in the 70s, used a GR bridge with separate signal generator and a good quality receiver for the detector. It was a lot of stuff to drag out to the tower(s) to make adjustments and sweep them for resistance and reactance. Don't remember how much max power was for the sig gen. One station had to shut down during the day as night time measurements were not possible even with sig gen at max.
Old AM tube transmitters I worked on used a crystal oven that was always on anytime the electricity was on into the transmitter. The filament on button would power up the low voltage dc stuff and filaments. After a time delay, then you could hit plate on for the transmitter to go on the air. Filament on would power up the oscillator. Usually left filaments on over night to keep mercury vapor rectifiers hot. Newer tube transmitters had some solid state stuff and may not have had a crystal oven and certainly no mercury rectifiers. So oscillator may or may not have been running when in standby. I'm real old school, never worked on all solid state rig.
Around here there was a Collins “Power Rock” (AM) that when it failed in a certain mode would broadcast a weak signal with another stations audio on it that was audible a good 15 miles away. Not good when the competition would show up on your frequency.
High power FM transmitters have an “Intermediate Power Amplifier” to boost the exciter power up high enough to drive the Power Amplifier. With a grounded grid, the power used to drive the PA needs to be a lot more than for a non-grounded grid. On the CSI (or like the AEL I dealt with) you could get quite a bit of signal through the final with the high voltage off.
High power FM transmitters have an “Intermediate Power Amplifier” to boost the exciter power up high enough to drive the Power Amplifier. With a grounded grid, the power used to drive the PA needs to be a lot more than for a non-grounded grid. On the CSI (or like the AEL I dealt with) you could get quite a bit of signal through the final with the high voltage off.
Somewhere, there must have been a junction in the transmitter that was detecting another nearby AM station and it ended up modulating some stage of the transmitter. Maybe our transmitter engineers can speculate further on how that would happen. Or a strong modulated signal could get into a low level stage and be amplified. That would probably be on the frequency of the nearby AM transmitter, or some intemodulation product.
Here's an intermodulation situation of interest to HGR1290. After WHGR 1290 went back to being a daytimer after Walmart bought the 3 tower array property, they moved next to the WUPS 98.5 tower. An engineer called me and said he noticed that there were spurious radiations on 99.7 and 99.9 and 97.1 and 97.3 during the daytime but not at night. They fixed the intermodulation problem and it went away. Clear Channel bought WHGR to put it off the air to upgrade WOOD 1300 to 20000 watts. Another application was later filed for another station that showed that the conductivities were so low that if they had had measured conductivities for both sites, WHGR could have stayed on the air. WHGR was then a daytimer so the night interference wouldn't have mattered.
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