The larger the diameter of the antenna, the broader the bandwidth. So an
aluminum self supporting vertical that starts with 3" diameter tubing
(the HD DXE starts with 4") can have twice the intrinsic bandwidth of
16ga wire. It also gets a bit shorter for same resonance frequency. I
had a guyed 80m vertical of 3" irrigation tubing which had about double
the bandwidth of a wire one.
Another choice is a simple fixed series capacitor with a shorting relay
to move the resonance up the band. I use 3 series caps and paralleled
relays on my 160m T to cover all of 160 in 50KHz steps, <2:1. It worked
out that the short, C, C/2, C/3 series values were right on to cover the
band in even steps. The untuned resonance is 1810KHz. Others use series
variable capacitors, but a vacuum variable is probably needed at the
smallest value of C. That costs a lot more than fixed 1KV caps and
takes longer to QSY.
Grant KZ1W
On 6/12/2017 20:29 PM, Mike Paskeuric wrote:
Hey Topbanders,
I was looking to buy or make a mono type 80 meter antenna for DXing.
I was wondering couple things. If I make a full quarter wave vertical WIRE
in tree 65 feet tall and see DX Engineering verticals claim 65 foot tall
but wider bandwidth. What is their secret or just advertisement?
Second question, I understand more radials make vertical better, but what
happens if one side half or one third the length radials due to space in
yard are shorter by 20 to 30 foot? Is it noticeable enough to buy a
vertical in middle of yard instead of wire in tree towards side of yard?
Dollars verses radial lengths.
Third and last question, can some of the radials, quarter of them,
overlap with radials of another antenna (160M mono vertical Gladiator
antenna)? Would it affect the performance noticeable.
I don't need long answers, just something to help out a bit.
Not sure what antenna to buy or make yet. I am in 2 and half acres and can
maybe stretch in field next to me some with no one knowing. Not many 80M
momo antennas to choose from.
It is a late Summer or Fall project so time to think.
Mike
n0 odk
73
thanks for suggestions gang.
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