|
Post by Druid Hills Radio on May 17, 2017 13:45:56 GMT
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 17, 2017 14:12:55 GMT
Arcing the Gap
Let's hear proposals for applying arc gap technology to part 15 installations.
|
|
|
Post by Druid Hills Radio on May 17, 2017 14:18:24 GMT
Arcing the GapLet's hear proposals for applying arc gap technology to part 15 installations. It should be noted that the Rangemaster 1000 internally employs a gas discharge device between ground and the antenna.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 17, 2017 14:30:49 GMT
Very Good to Know
On the "arc gap" question DHR responds: "It should be noted that the Rangemaster 1000 internally employs a gas discharge device between ground and the antenna."
Excellent point and of course the gas discharge device is a proven and inexpensive safety measure.
Another transmitter which includes a gas discharge device is the AMT5000 from SStran.
We guess that a gas discharge device can be added to any part 15 installation.
|
|
|
Post by Boomer on May 17, 2017 19:51:38 GMT
The gas tube could help against a harmful voltage rise on the antenna, static discharge from the wind, or nearby strike, it's probably very effective, but I don't think it would do much with a direct strike.
I was thinking how a ball gap like that could be added alongside of the main radiator at its base with the cold end connected to an earth ground. That might not save the transmitter, but less voltage would go through wires into the house, it would be bypassed.
Broadcast stations and their transmitters have a myriad of devices to reduce lightning voltage before it gets into the building, like a ball gap, coax cable rolled up, and ground strapping around the perimeter of the building.
The challenge with a Part-15 antenna install is doing all that stuff without reducing the amount of signal, because of small signals, high impedance on the antenna.
Most installs probably don't have to be worried about lightning too much, but if you're the highest point in an open area, or your install is planned on a building with lightning rods on it, I'd start to be much more concerned about lightning!
Boomer
|
|
|
Post by mark on May 17, 2017 21:26:06 GMT
The Decade MS-100 uses a coil across conductor and ground for protection of the output in case of static on the antenna. The coil has a very high impedence at FM frequencies but if a transient voltage occurs on the antenna the coil protects the output transistors by shunting the energy to ground.
Mark
|
|
|
Post by thelegacy on May 17, 2017 22:29:32 GMT
I was always wondering how to protect your transmitter from lightning. What about those lightning protectors they sold for CB Radio's back in the day I bet you could somehow use that too.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on May 17, 2017 23:24:18 GMT
At the Antenna Output
Mark mentions: "The Decade MS-100 uses a coil across conductor and ground for protection of the output in case of static on the antenna. The coil has a very high impedence at FM frequencies but if a transient voltage occurs on the antenna the coil protects the output transistors by shunting the energy to ground."
That sounded familiar so I looked at the schematic for the Ramsey FM30b and it has the same thing... a 2.2uH inductor from RF output to ground.
By contrast the Ramsey FM25B, which has approximately the same output circuit, doesn't have the RF output protected, so maybe anyone who has a 25B might want to add that part.
Now I'm curious about the C.Crane FM1 and FM2... hold on.... I'm looking...
YES to both... and the FM2 also has a diode from RF out to ground.
|
|
|
Post by Boomer on May 18, 2017 4:01:08 GMT
Thanks to Druid Hills, Carl and others, we're learning in a not too frequently discussed area, protecting transmitters from voltages coming IN, rather than only being concerned with what's going out.
I think it's more important now, with smaller output devices and more complicated microelectronics that safety from without is being acknowledged too.
|
|