Dennis and Dave
Evidence so far:
1. Experiments in loading 50 foot (15m) evergreen fir tree for operation
on 3.7MHz. 1.5metre diameter tuned loop and novel (G3LHZ) tuned coiled
hairpin tried as tree exciters. Both were tried horizontally around the
tree and vertically edge on and a few cms away from the tree. It was a warm
summer dayin the afternnoon, about 25C. In both cases the noise was about S7
on my FT897. The antenna bandwidths were approximately doubled as a
consequence of coupled tree loss. Only one incomplete QSO was made with
about 80 watts SSB. The loop was then placed horizontal on top of dry
grassed clay soil about 10 metres away from any trees. The bandwidth again
was about doubled over the free space value. That is about the same as the
coupled tree loss. The surprise was that the coupled ground loss was not
noisy. Less than S2 on the 897. No QSOs were attempted on the loop in this
position. With the loop vertical and about 1metre above ground several
satisfactory QSOs were made. Roadside 230v power lines wre more than 50m
away for all these tests. Loaded trees are both lossy and noisy. Keep away
from them.
2. In February 2008 in Port Douglas in Queensland (VK) using a Sony ICF
SW100 with extended whip to couple into a palm tree in a hotel courtyard. On
14MHz no readible signals on account of high noise level. But coupled to
metal gate of the swimming pool area (at about a fifth of the height of the
palm tree), the noise was much lower. Several JAs and Pacific stations
were heard.
3. Freeview digital TV has a marginal SNR on one of the two Crystal Palace
clusters at this QTH. There are deciduous trees at about 30m distance and a
bit higher than the TV antenna. No satisfactory copy is obtained until the
outside temperature is a couple of degrees below zero. This is not
apparently correlated with 'lift' condtions. And it has been observed on
many cold nights and days. Now I put this down to bio-electric noise
probably associated with the pumping of the sap to the top of the trees.
This process appears to close down at low temperatures.
When I get time I will measure noise at 500kHz. Probably with a multi- turn
tuned loop.
But it does look as if you have power line noise problems anyway. In general
I do not.
73 - Mike - G3LHZ
----- Original Message -----
From: "Dennis" <[email protected]>
To: <[email protected]>
Sent: Thursday, August 20, 2009 3:19 PM
Subject: Re: LF: Re: Tree noise
Dennis (DL6NVC)
Please could you try your loop away from the tree. Preferably more than
2
metres. I have found severe bio-electric(?) noise from trees from 3.5 to
500MHz.using loops, whips and UHF Yagis. The noise drops to almost zero
if
the tree ambient temperature is below about zero Celsius.
Mike - G3LHZ
Hi Mike, this is a really amazing statement! I'm going to investigate this
somewhere in the nature, kilometres away from cities and villages!
Yes, the tree obviousely will act as a "black body radiator" at (hot sunny
day today) >300 Kelvin. But does this matter to 500kHz or shortwave? I
don't believe it. But with UHF and SHF weak signal communication, this
thermal noise would clearely be an important issue.
Since yesterday, I actually have 3 loops up and running:
1. 10m loop, linden tree, nearest end about 5m from the house, abt 15m agl
2. 10m loop on the balcony, outside but close to the house
3. abt. 12m indoor loop
I must tell you, that the loop inside the linden tree delivers by far the
best signal-to-noise, the balcony-loop is worse, and the indoor loop is
even much much worse.
The broadband noise seems to travel along the mains wiring. When I simply
touch the soldering iron, when I connected the central heating as
"ground", this all causes increased noise.
Think, some or several of my neighbours are using powerline communication
systems.
vy73
Dennis
DL6NVC
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