The Power of AM (Spark Gap Shorting)

[Info-warrior]

This is a video of one tower in an AM's array that had it's spark gap damaged after an ice storm. This tower wasn't connected to the transmitter at the time, but was picking up the signal from the other tower.

I can only imagine how loud the sound of the arc must have been in person.

http://video.google.com/videoplay?d...715&start=0&num=10&so=0&type=search&plindex=0

 

[Neil E.]

Interesting video and thanks for the link. I do have to wonder who was taking the video. If they were on the tech crew for the station I also have to wonder why they didn't jam some insulating material between the balls. Seems as if, considering the arc length, that plywood or wall board would have stopped the arc. Why stand there watching the metal get burned by the arc? Oh well, I wasn't there was I?

Neil

 

[kyscott]

somebody was moving that outside ball! Look closer at the video.

 

[OKCRadioGuy]

Yeah.. I think they are trying to draw an arc for demo purposes. With that being said, I used to work for a 50k that had a 80 foot tall STL tower pretty much built right in the major lobe of this 3 tower classic 1/2 wave array. The impedance of this b-och was high enough the first fairly large bowl insulator arced right over after the consultant got the de-tune skirt tuned. He was very supprised it did it. A larger bowl insulator had to be installed. A neat trick I would do from time to time is go kick the station in omni and down to about 5k. I'd strap across the detune back to ground, then turn the power up and slam it on directional. I could remove the short and pull an arc of blue and red blazes almost 2 feet wide complete with buzzing modulation sound. It made for one HELL of a show.

 

[Tom Wells]

The arcing and shorting would have been quite audible to listeners with that amount of power being shunted.

 

[awsherrill]

Cool video.

Reminds me of the experience at our 50kW AM a couple years ago. This particular site has a day tower and a separate two-tower night array, all big self-supporters. One day the tower lighting conduit on the day tower fell apart and shorted the tower (pretty spectacular, lotsa smoke and flame).

We had to thoroughly clean up the lighting choke box, install a new insulator, and replace the horizontal run of conduit that had broken. We put the station on the night array, dropped to 5 kilowatts, grounded the day tower, and STILL were drawing impressive arcs anytime the conduit touched grounded metal. That day tower was picking up a helluva lot of RF from the active night towers.

 

[dave388]

Interesting video and thanks for the link. I do have to wonder who was taking the video. If they were on the tech crew for the station I also have to wonder why they didn't jam some insulating material between the balls. Seems as if, considering the arc length, that plywood or wall board would have stopped the arc. Why stand there watching the metal get burned by the arc? Oh well, I wasn't there was I?

Neil

here is something i grabbed after that vid. video of ice falling from a 1600ft tower
http://www.youtube.com/watch?v=pfBp2QYOIbc

i wonderd the same thing, why didnt the guy taking the vid. slap a piece of plywood between the balls.

 

[kyscott]

i wonderd the same thing, why didnt the guy taking the vid. slap a piece of plywood between the balls.

Because as I said earlier, they were making it arc on purpose.

 

[RadioFixerCLE]

It's an excellent way to instill respect for RF in newbie engineers.

Awesome thing. Especially hearing the signal as the spark flashed.

AM is king.

 

[nd2023]

It's weird to hear the modulation in the spark. It's like making a radio in thin air.

 

[rrsounds]

i wonderd the same thing, why didnt the guy taking the vid. slap a piece of plywood between the balls.

Because as I said earlier, they were making it arc on purpose.

As cool as it looks (and sounds) the arc is pitting the bejesus out of those balls. Gonna have to put in some serious raspin' and filin' time to smooth them out again.

Kind Regards,
David

 

[nmoore6676]

I've heard reports of people near high power transmitters getting the sound out of lots of unlikely places. What I wonder is what about the people who live or work near these installations and have large metallic objects around. I realize that this was a resonate tower but it's only 5KW too.

Here in North Hollywood we are near KSPN (formerly KMPC) which is 50KW days, 10 at night. There are a whole bunch of buildings around the KFI site in Buena Park, which were thankfully missed in the tower collapse. Then there is KTLK and KTNQ, both 50KW each with their towers inside of wells embedded into an industrial warehouse complex. A full 100KW of RF floating around the area waiting to leap off something.

I've experienced mild RF shocks in the past and they are no fun. A burn can be very serious if you get an arc over to the body from something hot with RF.

 

[RadioFixerCLE]

I've heard reports of people near high power transmitters getting the sound out of lots of unlikely places.

I remember hearing something -- that now I realize was WCBS Newsradio 88 -- on my aunt's telephone after you dialed a number and were waiting for the other party to pick up or if you got put on "hold". I was about 8 or 9 years old by then and I always wondered why someone was doing a -- fairly faint but distinctively audible - newscast over the telephone. Maybe it was a courtesy service from NY Telephone?

We lived in Astoria, Queens Cty. which is fairly close as the crow flies to High Island in Bronx Cty. (where 66 and 88 share the stick). AM 88's signal is very strong in Long Island City and Astoria (to the point of overloading the front ends on some radios and cuasing the station to appear at two adjacent spots on the dial)

Years down the road, the situation was apparently fixed. My grandmother noticed that and she wondred aloud "why they had taken the news off the phone".

As a teenager (still living in the same neighborhood), I was futzing with an old hot-chassis solid-state radio. I had (stupidly but naively) disconnected the speaker from the radio itself....but I kept hearing sound. Could it be coming from the radio? Hmm....I spin the tuning knob and sure enough....the stations start changing!!! It was coming from the output tranny's laminations!! Unbelievable. :

Good thing I didn't blow the output transistor on that radio (a high-voltage one) :-[

 

[nmoore6676]

I've heard reports of people near high power transmitters getting the sound out of lots of unlikely places.

I remember hearing something -- that now I realize was WCBS Newsradio 88 -- on my aunt's telephone after you dialed a number and were waiting for the other party to pick up or if you got put on "hold". I was about 8 or 9 years old by then and I always wondered why someone was doing a -- fairly faint but distinctively audible - newscast over the telephone. Maybe it was a courtesy service from NY Telephone?

We lived in Astoria, Queens Cty. which is fairly close as the crow flies to High Island in Bronx Cty. (where 66 and 88 share the stick). AM 88's signal is very strong in Long Island City and Astoria (to the point of overloading the front ends on some radios and cuasing the station to appear at two adjacent spots on the dial)

Years down the road, the situation was apparently fixed. My grandmother noticed that and she wondred aloud "why they had taken the news off the phone".

As a teenager (still living in the same neighborhood), I was futzing with an old hot-chassis solid-state radio. I had (stupidly but naively) disconnected the speaker from the radio itself....but I kept hearing sound. Could it be coming from the radio? Hmm....I spin the tuning knob and sure enough....the stations start changing!!! It was coming from the output tranny's laminations!! Unbelievable. :

Good thing I didn't blow the output transistor on that radio (a high-voltage one) :-[

In the old days the Bell people would put a capacitor across the transmitter (microphone) in your phone to suppress that interference. Ham radios could do it too.

As to your '"solid state" radio I believe what you had was one of the old series wire filament sets where they used a line up of tubes with filament voltages that added up to 110. That was the reason for the tube numbers greater than 6 or 12. The first numbers were the filament voltage and the letters and numbers after were the tube model (configuration). One side of the line went to the chassis ground and so if you plugged it the wrong way the thing was hot. Even the early transistor sets for AC operation needed a transformer to reduce the voltage before rectification. I got bit enough in my childhood tinkering days to know this from experience.

But I do recall hearing the audio output transformers on PA amplifiers and high end radios "sing". You may have your memories a little mixed because those kinds of radios with the more massive transformers were higher end. The smaller sets had a puny little transformer sometimes it was a part of the speaker and didn't have enough metal to be heard very well.

 

[RadioFixerCLE]

As to your '"solid state" radio I believe what you had was one of the old series wire filament sets where they used a line up of tubes with filament voltages that added up to 110. That was the reason for the tube numbers greater than 6 or 12. The first numbers were the filament voltage and the letters and numbers after were the tube model (configuration). One side of the line went to the chassis ground and so if you plugged it the wrong way the thing was hot. Even the early transistor sets for AC operation needed a transformer to reduce the voltage before rectification. I got bit enough in my childhood tinkering days to know this from experience.

Nope. This was a "hot chassis" transistor set. The output transistor ran directly off the mains AC supply via a dropper resistor. In fact, I still have that radio (I collect old radios). These things were popular in the 1970s and even into the early 80s.

Look at this website: http://www.geocities.com/wa2ise/radios/amcirk.jpg & http://www.geocities.com/wa2ise/radios/ss.html

 

[nmoore6676]

As to your '"solid state" radio I believe what you had was one of the old series wire filament sets where they used a line up of tubes with filament voltages that added up to 110. That was the reason for the tube numbers greater than 6 or 12. The first numbers were the filament voltage and the letters and numbers after were the tube model (configuration). One side of the line went to the chassis ground and so if you plugged it the wrong way the thing was hot. Even the early transistor sets for AC operation needed a transformer to reduce the voltage before rectification. I got bit enough in my childhood tinkering days to know this from experience.

Nope. This was a "hot chassis" transistor set. The output transistor ran directly off the mains AC supply via a dropper resistor. In fact, I still have that radio (I collect old radios). These things were popular in the 1970s and even into the early 80s.

Look at this website: http://www.geocities.com/wa2ise/radios/amcirk.jpg & http://www.geocities.com/wa2ise/radios/ss.html

Cool! Thanks for sharing I missed those.

I did build some similar stuff from schematics I got from Popular Electrics, I think, but they used an isolation transformer in the power supply. If you wanted a case you had a friend who did wood working build it or put it into an old bakelite radio case. I also remember TV sets that used the series filament trick too. What I have always wondered is why they didn't have those polarized plugs that come on everything today.

 

[Tom Wells]

The AM radio pickup on phone lines has been gone since (each customer's) long line back to "central" was replaced with a multiplexer and or fiber link to the network the multiplexer replacing huge amounts of copper.. The remaining shorter copper sections back aren't usually enough to cause the problem.

Her ancient phone probably had two reversed biased diodes as a limiter right at the earpiece.
They made a handy AM detector all right.
The newer "active electronic" phones are sometimes very bad at RF rejection because they are chockfull of semiconductor
junctions just waiting to rectify some RF. In strong fields, anyway.

You were lucky the output transistor didn't blow.
It is would be unusual if someone had set up a circuit design conservatively enough to withstand "no speaker" if DC coupled.
Transformer coupling saves the day.
Only the secondary was disconnected, the resultant load reflected back through the xfmr at a normal level was
not enough to hurt itself. If you'd turned it WAY up you'd most likely have zapped the output

 

[Tom Wells]

Now here's a healthy spark.

video.google.com/videoplay?docid=4468957986746104671

 

[fm-engineer]

arcs are quite different from sparks.

 

[xmtrland]

I love that one. Ran across it last night, played it several times. Oh the old days of radio when your plate supply hooked directly to the AC on the pole with no Step down transformer.

I also remember when KIRO (50KW nd day/50KW DA2 night) did tower maintenance on the night tower. The energy from the day tower running 50KW was impressive when grounding out the night tower when the station was running ND of course. Even midnight maintenance was fun because you had KING pumping out 50KW about ½ mile away with their 3-tower array. I hear its even better now that they added 770 50KWD 5KWN to the 1090 (king site).

My dad who also watched the KIRO transmitter site on weekends. Cut and bailed the field around their two tower array for hay. One day while bailing the field (the bailer is real noisy and he wore the big heavy duty hearing protectors.) he started to hear the station loud and clear above the noise of the bailer and with the hearing protection on. He looked over at the day tower and saw a continuous ark across the two ark gap balls at the base of the tower. Just flashing and singing to the voice (KIRO is news talk). He stopped the bailer and had to cycle the transmitter to make it stop (he was suppressed the Magnaphase on the 317 didn’t kick the transmitter off). Once the transmitter was cycled off then on it stopped. Upon inspection of the tower he found a few feathers and figured a bird had landed across the spark gap, starting the arc. Wish I could have seen and heard that.