On Wed, 2 Aug 2006 21:33:33 +0200, "Antonio Vernucci"
wrote:

hard to tell how many dB one would loose, until the power loss mechanism via the rod coupling is understood. I would need to find somebody who had occasion to test that configuration, otherwise I will have to anyway buy the rod (about 100$) and make the test myself

Hi Tony,

That is the only sure way of knowing. Modeling with EZNEC will
certainly reveal obvious problems.

As for heating. The exposure to sun (if the rod is black) will
probably create more heat than the RF.

I am not worried at all of rod heating, but of RF power loss

Same thing.

There are many articles on the Internet that suggest a resistance in the order of one ohm or so. But knowing precisely how many ohms the rod shows woud not help much, as, again, until the loss mechanism is not characterized, noone can stell something sensible

Total resistance over 8 meters is 1 Ohm? If so, it does not look like
a problem. 1 Ohm every 10cM? Still does not look like a problem.

Download EZNEC and do your own modeling.

73's
Richard Clark, KB7QHC

Richard,

Can you assign different conductivities to different wires in EZNEC? I
don't think you can.

You could distribute the resistance, 1 load per segment each having a
resistance of 1/#segments of the total. It seems important for
coupling to have a realistic diameter (fat) wire for the carbon fiber
pole, but it needs to be lossy.

A load taper from bottom (large tubing, lower resistance) to top (small
tubing, high resistance) would be easy to implement as well. This is
probably only worth it if it seems that the loss will be nonnegligible,
but it could take into account the effect of the element current
distribution on loss.

Dan

That is the only sure way of knowing. Modeling with EZNEC will
certainly reveal obvious problems.

Yes, that is a possibility, although properly interpreting EZNEC results is often not easy. I will try anyway

Total resistance over 8 meters is 1 Ohm? If so, it does not look like
a problem. 1 Ohm every 10cM? Still does not look like a problem.

Well, one ohm is just the order of magnitude. It will be neither one tenth of a ohm, nor 10 ohms. Moreover resistance will vary along the rod due to the very significant diameter change, and RF current is not constant along the rod either. I am beginning to fear that the only way to really understand how things go is to buy the rod, build the antenna, apply high power ( 1kW) to it for 15 minutes, and the touch the rod to determine whether its temperature has raised somewhat.

73

Tony I0JX