I don't know of a reason that insulated or grounded elements should make
a difference, IF all else is identical. what W8JI has to say
https://www.w8ji.com/pecipitation_static.htm ; Same height AGL may not be
the criteria for some noise.
Some thoughts:
What I've experienced that does matter is the pattern - F/B, F/S and
details of what higher angle lobes might look like. My 40m Moxon is
noisier (not by 3 S units) than my 3L full size 40m. Different heights,
thus different peak elevation gains, but also large differences in F/B,
F/S and high angle lobe. Same results for my 4L steppIR vs
monobanders. Some of the following are also likely contributors to the
differences.
You don't mention the band you measured, is it the same delta 10-15-20?
Are the coax routings the same to the towers? (buried better than
catenary) Is there much difference in the coax route ability to pick up
noise? How are they routed and ground at and up the tower? (routed
inside and grounded top and bottom) Same shack end ground/bonding
panel? Is the mast grounded for both? (jumper around rotator
bearings) Noise sources nearest the towers?
F12 balun? Not sure what it's choking capability is, others have
commented re chokes.
Any chance a driven element insulator is degraded? UV? Arc path? Dirty?
"Both are fed with 1/2" Heliax" - nice but I hope not for the rotator
loop as it is known that cracks develop in the shield = noise.
Investigating most of the above might be simpler and cheaper than a new
antenna. But, if it isn't the antenna choice then back to same
problem. Or swap antennas on the towers, but a bit of bother.
Grant KZ1W
On 8/19/2018 10:40 AM, rlvz--- via TowerTalk wrote:
Hi Guys,
I believe some HF Yagi antennas receive more noise than others and I'm
wondering if any of you have noticed the same thing?
I've got two Tri-Banders located on different towers, in the same yard, at aprx. the same height AGL, and one of them receives 3 S-units more noise, on average, than the other when the antennas are pointed in the same direction regardless of what direction they're aimed, though the received signals are usually identical.
More specifics: both use the same model Force 12 Balun, both are fed with 1/2" heliax, and both go to the same Stackmatch antenna switch. One antenna is a Hy-Gain Tri-Bander which has grounded elements including the Driven Element which is grounded at the boom through it's Beta Match, and this is the "quiet" antenna. The other is a Bencher Skyhawk which has it's Driven element isolated from ground. I'm wondering if the Hy-Gain may be quieter since the Driven Element is grounded at the boom which the Skyhawk isn't?
By the way, I ran the test of disconnecting the shield of the PL-259 at the shack end of the Skyhawks coax to see if the antenna got quieter or noisier to determine if the addition of a "Noise Balun" would reduce noise on the Skyhawk. The noise level increased with the shield disconnected, so I'm told a Noise Balun like Palomar produces wouldn't help reduce noise on the Skyhawk.
I ask this question because the Skyhawk is too noisy for weak signal work and I'm thinking of replacing it with another Tri-Bander that has a grounded Driven Element if it's likely to receive less noise.
Thanks in advance for your thoughts.
73,
Dick- K9OM
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