Ken,
Ken,
While browsing the forum I came across a post of Ken Norris where he mentioned that he broadcast from a boat grounded to the water... That little tidbit immediately got my attention, because I've been planning on buying a 30ft or so used sail boat sometime in the next 6 months or so..
Several years ago I had a Rangemaster mounted on top of the Tybee Island Pavilion, and grounded to the existing copper grounding of the structure.. The range I achieved was amazing.. perhaps too amazing, I was able to pick up a strong clear signal on the next island over - about 5 miles away. I'm certain this was due to the elaborate grounding system... I also think that the grounding system probably is what caused my transmitter to go out after about 2 months.. It just quit transmitting!
After a call to Keith, he had me sent it back, and he fixed it.. "The gas tube that provides lightning protection was damaged."
He replaced the gas tube, and sent the working unit back to me, but the same weekend I received it, someone stole it before I even had a chance to take it out of the box!
Excuse me - I have totally wandered off the subject! My point is that I think my incredible range was due to the fact that the heavy copper wire/tubing which the pavilion has went in 4 directions from the roof and went down the sides, deep into the sand where it was wet with the atlantic ocean.. Which brings me back to the subject of Ken Norris using the water as a ground.
I would appreciate hearing some thoughts from Ken himself and others on setting up a station on a sailboat docked at the marina.
One thing that concerns me is a docked sailboat is naturally going to rock a little, even in calm weather.. Wouldn't that reek havoc on tuning the transmitter, and keeping it tuned?
As for the ground.. what do you do? - Simply run the wire under the boat?
And what of the processing equipment and computers? How would it fair with the dampness of a boat?
Hi Rich,
"I would appreciate hearing some thoughts from Ken himself and others on setting up a station on a sailboat docked at the marina.
One thing that concerns me is a docked sailboat is naturally going to rock a little, even in calm weather.. Wouldn't that reek havoc on tuning the transmitter, and keeping it tuned?
As for the ground.. what do you do? - Simply run the wire under the boat?
And what of the processing equipment and computers? How would it fair with the dampness of a boat?"
Mine isn't a sailboat, it's an oiler, 1969 Owens lapstrake, and although it runs, it's basically a dock queen, doesn't go out. But before we discuss anything about grounding your TX you need to familiarize yourself with boat grounding systems if you haven't done so. There's more to it than meets the eye, particularly if you will be connected to shore power ...
http://www.sailmail.com/grounds.htm
As far as the boat rocking goes, it's hard to tell. We've had some severe windstorms, up to 50 knot gusts in the marina, and boat movement doesn't seem to make much detectable difference, but it's not nearly as high as a system mounted on a sail mast ... the arc of sway would be far greater. Not sure what that would do, but tuning is a system thing, i.e., the movement might merely cause a little wavering of the signal when it happens, but shouldn't throw the system out of tune per sé.
Dampness is always an issue, even on land in the NorthWest. You can't let heat go down very far, things have to be kept dry where it counts. My boat is wood, and it barely sweats on the inside, but a fiberglass hull is a totally different story.
Except for improper grounding, I can't see how a grounding environment as you described it could hurt the transmitter, i.e., IMO something else must have caused the gas-tube lightening arrestor to get damaged.
While driving, the auto antenna is in motion and changes can be detected in reception, with AM strongly affected by changes in ground terrain. The differences in FM reception are best observed on low power signals which also seem to vary based on terrain, but in big cities the high power FMs usually compensate with brute strength.
When analog TV was turned on, we had channel 30 up on a 1-thousand-foot tower, and during heavy wind storms when that tower must have swayed several feet the reception indoors followed the sway (so it seemed) by going in and out of multipath ghosting.
Carl,
Most modern receivers have a circuit concerned with automatic signal gain control, or AGC. A great number of consumer receivers have no way of turning this feature off. In FM receivers there is also the automatic frequency control. When these 2 circuits work in tandem, actual signal variations are covered up in the receiver. This interaction makes the signal strength indicators in most receivers only a approximation of the signal strength.
Additionally, if the stereo decoder in an Fm receiver is switched on and off momentarily, perceived signal strength by audio quality can also be very misleading.
AGC circuits in AM, FM and TV were developed to provide the receiver's detectors and demodulators a constant signal level so that consumers were not bothered by the rise and fall of the received signal.
"Ghosting" is caused by multipath signal distortions in the receiver. The primary signal is followed by a short delay of the reflected signal causing a secondary image on the TV screen. The same kind of audio multipath distortion can be introduced into FM radio receivers as well.
And finally, a vertical oriented antenna would have to "heel over" by 30 degrees or more to override the effects of the receiver AGC or to decrease the perceived signal strength. That kind of "list" would sink most small power vessels depending on the freeboard of the vessel. There are several variables at work here, so actual world and anecdotal evidence is what counts here. Most likely the only people who would notice are the folks who are already listening to a very noisy signal already.