I could increase the ground radials substantally over approx 90 degrees into the garden, as much as 30+ metres across the garden.
Also if it would be worthwhile, i can bury numerous earth rods, and silver solder them, if that would help ?
I also have found a book by Orr and Cowan, that states if using short ground radials, connect all the outer radials with a ring of wire, like a rim of a wheel, would that help ?
I am just looking for ways to make the best of what i have got.
Thanks again,
Paul.
A vertical buried ground rod at the base of the monopole and connected to the common point of the buried radials could be helpful in lightning protection, but wouldn't have much effect on the r-f resistance of the buried radial system at the operating frequency. But probably (if properly grounded) your 75m tower 14m away already gives some protection to your MW system, at least for direct hits.
Connecting the open ends of buried radials together with a ring of wire will set up alternate paths for the r-f currents flowing on the buried wires, which can increase the loss of the radial system.
With enough radials, earth currents near the wires are captured without much loss, due to their short paths through the earth to reach the radials.
Would you recommend insulated or bare copper wire for the radials ?
From what i am reading, there seems to be differing opinions on this.
Also i can extend the radials in to the embankment by hammering in earth rods horizontally, just under ground level, or at least a few of them, would the rising embankment reduce the effectiveness of these rods due to increased earth height?
Thanks again,
Paul.
Insulated, buried radials work as well as bare ones as far as r-f loss at MW operating frequencies. But bare ones would be better if no buried ground rod was used at the tower base and connected to the common-point of the radials.
No harm in using horizontal ground rods under the embankment, especially if they are driven in within 6-8 inches of the ground elevation of the embankment. But any improvement in the r-f performance of the radial system you are thinking about (with longer, denser radials in some sectors) will be hard to detect.
This might be useful information from my experience...
Operating at 1680 lHz I was perfectly able to receive the signal on a portable radio in front of the building, a 100' downhill slope.
However the backyard's 100' uphill slope had no reception at all by the top of the hill.
What I did was slap a radial on the ground going most of the way up the hill. To balance it I ran an equal radial in the opossite direction which fed through the basement and into the garage.
Result - perfect reception not only at the top of the hill but for five or six blocks south, uphill most of the way.
Carl,
I have always thought the longer ground radial , compared to the rest, would enhance signal in that direction.
At the moment the steel tower (14 metres away from am antenna), is not currently earthed, i am going to do a substantial lightning protection with 4 long buried earth rods and thick conductor.
Rich, if i were to link my am antenna radial/s to the tower earth rod closest to each other,would this offer much benefit ?
Paul.
if i were to link my am antenna radial/s to the tower earth rod closest to each other,would this offer much benefit ?
Not much as far as improving the r-f ground provided by the radials converging under your MW monopole.
Ground currents are strongest closest to the base of a vertical monopole.
Thanks for the replies to the questions i have be asking.
One odd idea i have always wanted to try is to run an insulated wire internally in the flag pole, with it connected at the top, and bring this insulated wire out through a hole at the insulator level, then connect this wire to the tx.
So the tx is connected to the top of the antenna, but through the internal insulated wire, any ideas how that would perform ?
Paul.
essentially that configuration should radiate the same as the flagpole alone, when driven at its base. Not sure what feedpoint impedance the system with the internal wire would have.
I believe the RF going verticaly up the wire to the top of the pole will be at opposite phase of the RF traveling down the pole and cancel out most of the signal.
My testing has suddenly stopped for the last 3 days due to internal water leak in the house, that was out of sight, and caused a lot of problems, must have been leaking for months.
Soon i will be able to resume my testing.
Rich, a question,
3 metre antenna on 3 metre support pole, or 4 metre antenna on 2 metre support pole.
Which one would radiate the best ?
Thanks,
Paul.
... 3 metre antenna on 3 metre support pole, or 4 metre antenna on 2 metre support pole. Which one would radiate the best ?
Other things equal, a system consisting of a ~3m whip and using a 3m support pole and 3m conductor to an r-f ground would radiate better.
The reason for this is that its radiation resistance is greater than that of the other choice given.
Interesting, so what would be the ultimate 3 metre compliant antenna+ground setup ?
If a capacitance top hat could be used, without it being measured as part of the antenna+ground length, would this uber setup consist of the 3 metre flag pole, with it's base connected to ground radials, then the tx mounted on the top of the flag pole with tx ground connection connected to the top of flag pole, and the capacitance top hat connected directly to the tx's antenna connection ?
The amt5000 would be used,with it's internal loading coil.
Thanks,
Paul.
If a capacitance top hat could be used, without it being measured as part of the antenna+ground length, would this uber setup consist of the 3 metre flag pole, with it's base connected to ground radials, then the tx mounted on the top of the flag pole with tx ground connection connected to the top of flag pole, and the capacitance top hat connected directly to the tx's antenna connection ?
Using the original NEC model but changing the monopole to a single, 3m conductor driven at the top as you decribed, with its base connected to the common point of the original set of radials in 4 mS/m earth shows a field of 126 µV/m at 1 mile, for 90 mW of power applied to the input of a 15-ohm loading coil. That is similar to the field shown in Reply 22 here for a longer vertical section.
This top-driven configuration would need about 400 µH in series with the feedpoint for system resonance on 1512 kHz.
Getting power and audio to the transmitter without operational problems may be a challenge, though.
Thanks Rich for the infomation.
Do you think there would be an optimal tx insertion point in the 3 metre length that would offer improved signal strength ?
Myself i would guess that if any, it would be in the middle ?
Thanks,
Paul.