Topband: Blessed With Too Many Trees?

[Jim Brown]

On 12/31/2012 8:02 AM, Wayne Willenberg wrote:
> The problem I may have is my house is located on about 21/2 acres of
> landscaped land that is surrounded by a forest in the remainder of the 5
> acres.

Hi Wayne,

My QTH in the Santa Cruz Mountains is in a very dense redwood forest, 
and I've tried to learn as much as I can about how they affect my 
antennas.  I've operated all bands from 160M to 450 MHz, an FM talkie on 
1.2 GHz, and use a cell phone in the 800 MHz and 1.8 GHz range, and just 
bought a couple of 900 MHz Motorola radios that I'm about to fire up on 
a ham repeater system.

My take on the issue, which seems to agree with what science I've seen 
published on the topic, is that vegetation, including tall trees, has 
little if any effect at HF, but begins to show attenuation in the VHF 
range that becomes increasingly significant with increasing frequency.  
No cell phones work up here in the mountains, and I see a lot of 
attenuation of UHF broadcast signals. Jim Lux, an EE who works at JPL 
and is a contributor to the ARRL Handbook, has done some serious 
literature searches, and come up with similar conclusions.  Google 
searches will, for example, find extensive published work on attenuation 
at VHF and UHF in jungles, and I've seen believable anecdotal comments 
from guys installing cell phone networks in Georgia pine forests 
indicating strong attenuation at those frequencies.  When I moved here, 
WA6NMF, my neighbor and colleague on the AES Standards Committee a very 
serious engineer who has been building VHF and UHF systems for most of 
his adult life, said to me, "Jim, at cell phone frequencies, think -3dB 
per tree."

My 160M antennas are all verticals with the best radial systems I can 
do, and I just worked #130 on Topband since moving here seven years ago. 
All my other antennas are horizontal, all surrounded by the trees, and 
at least 60 ft below the top of those trees, and I just worked #301.  So 
I'd say from an MF and HF point of view, consider them a blessing -- 
organic antenna supports -- and don't waste much effort above 100 MHz.

73,