On 3rd November, John wrote:
"...I have at present 4 - 130' radials attached...
Question is, without involving "Murphy", is if I add more radials will the
vswr change in that I might have to shorten the antenna, will me signal
strength
change with addition of more radials, will I gain anything by adding more
radials..."
**********************************
Hi John,
Welcome back to Top Band! With 145 DXCC confirmed therein, you're already
the envy of more than a few on the band, I'm sure, yours truly included, Hi
Hi.
I'm hardly any sort of a "ghuru" when it comes to the matter of ground
radials, but I've learned this much, FWIW: the more radials you add, the
less the ground losses at the base of your antenna, and the greater the
radiation efficiency of your signal.
Do you have a copy of the latest ARRL "ANTENNA HANDBOOK" (20th edition), or
ON4UN's excellent "LOW-BAND DX'ING" (4th edition)...? If so, take a look at
pages 3.9 - 3.10, and pages 9.13 - 9.14, respectively: in a nutshell, the
optimum number of radials --- that are 1/4-wave long, that is --- is 90.
This results in a net power loss at low angles (with a 1/4-wave radiator) of
0.5 db., and will give you a feedpoint impedance of 37-ohms.
As I understand it, resonance effects apparently disappear once you have the
optimum number of radials installed beneath your antenna, at which time they
collectively act more as a "ground screen", as opposed to acting like
individual wires...
There is a LOT of information to be digested in both books, & I strongly
recommend you obtain them...they ARE well worth the price, and then some.
There is a particularly interesting table on page 3.10 of the "ANTENNA
HANDBOOK" that I think would especially intrigue you. It summarizes the
OPTIMUM number of radials --- based upon length --- and it goes something
like this:
-0.1-wave = 16 radials;
-0.125-wave = 24 radials;
-0.15-wave = 36 radials;
-0.2-wave = 60 radials;
-0.25-wave = 90 radials, and,
-0.4-wave = 120 radials.
It all boils down to MAXIMIZING potential performance, whilst at the same
time MINIMIZING cash outlay for wires! In your particular case, with four
1/4-wave long wires, you could maximize performance at the MINUM level on
the table by cutting your total 480' of radial "stock" into 10 lengths,
0.1-wave long (48' each), and then procuring another 288' of wire to be cut
up into six additional 48' lengths, thus yielding you a final grand total of
16 radials at 0.1-wave long...
According to the table, your net power loss with this new configuration
would be 3 db., & your feedpoint impedance would be 52-ohms.
I'm sure others reading this--- with far more experience than mine --- will
have a LOT more to say in this regard...be prepared to take notes! Hi Hi.
~73~ Eddy VE3CUI - VE3XZ
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