[600MRG] Could my antenna be a very large Dummy Load ? - Long Reading

[patrick hamel]

Eric,
You are right, but in my case (WD2XSH/6) I was running a KW DC input for a clean 300 watts output into a total loss and radiation resistance measuring over 28 ohms leaving the tuning box.
The radiation resistance of a "perfect" antenna of the same height was 0.77 ohms, so most of the power was heating the 27+ ohms of trees, sheds, houses, and dirt.
I think I was getting 15 watts erp based on the antenna current through the "perfect" antenna Rr.
Getting the fat part of the RF curve up the wire did have an effect on the results for the same antenna current.
I am in a city with lots of trees, houses, paved streets,fences, railroad tracks. 
All the power wires are above ground and I never had a calibrated field-strength meter to prove things. 
73,
Pat W5THT & WD2XSH/6

 

----- Original Message -----
From: "Eric NO3M" <no3m at no3m.net>
To: "patrick hamel" <pehamel at cableone.net>, 600mrg at w7ekb.com
Sent: Thursday, October 12, 2017 9:29:47 PM
Subject: Re: [600MRG] Could my antenna be a very large Dummy Load ? - Long Reading

Pat

Consider your last line:

> We all have a lot to learn with the 5 watt erp limit.

With an EIRP limit, it's not necessary to keep chasing after loss 
reduction, efficiency, etc. like it is for say a 160M antenna.  The 
beauty of an EIRP limit is that we can tolerate some losses, how much 
depends on 1) how much power you can generate up to a TPO limit, 2) how 
much power you are willing to waste due to losses, 3) you are prepared 
to deal with the potentially obscene RF voltages.

Hams are used to TPO limits, and increasing efficiency (reducing losses, 
etc.) or manipulating an antenna's pattern (arrays, etc.) is the only 
way to improve the situation beyond the 1.5kW TPO limit.  A guy with a 
1% efficient antenna and another with a 20% efficient antenna, both with 
the appropriate TPO's to reach the 5W EIRP limit, should in theory have 
the same far field signal strengths.  The alternative to raising your 
coil would have been applying more power to get the same result.  
Whether that would have been feasible or not depends on the points (1-3) 
above.

73 Eric NO3M / WG2XJM


On 10/12/2017 09:34 PM, patrick hamel wrote:
> Please, People, "get as much wire in the air as possible" really means "get as much current to the top of the vertical as possible" in a ground-mounted vertical.
> AGAIN "get as much wire in the air as possible" really means "get as much current to the top of the vertical as possible" in a ground-mounted vertical.
>
> OK, so I went overboard with the 10 foot wide 11 wire 120 foot-long capacitive loading and hanging the fiberglass coil bolted to the copper pipe spreader.
> Before hanging the coil up there I had a base loading coil and almost no QSOs after Sandy (WD2XSH/2) who lived close by in Louisiana had to QRT.
>
> My big mistake was to feed it like an inverted L antenna and have the radiator 10 feet from the support tree at the end which really changed the losses when the sap froze one year.
> Rudy's writeup about his counterpoise makes the antenna a "C" configuration which is no longer a ground-mounted vertical. Remember he said there was several thousand volts between the counterpoise wire and ground!
> Remember the current through an open circuit is zero, even at the end of an antenna or counterpoise wire.
> You want to move that point so that the current in the radiator is maximum all the way up, or go with the counterpoise.
> We all have a lot to learn with the 5 watt erp limit.
> 73,
> Pat W5THT & WD2XSH/6
>
>
>