In years past, part of my work involved signal propagation (VHF/UHF)
predictions and measurements.
For 150 MHz paging service, the generally accepted in-building
attenuation figure was on the order of 10 to 20 dB compared with an
outdoor measurement in the same location. 10 dB or so for typical timber
framed residential construction, 20 dB for reinforced concrete
commercial or multi-unit residential construction, and 30 dB in some
particularly difficult environments with many interior walls and with
high local noise, such as a telephone company switching center.
Almost all the recent literature concentrates on 800 MHz and upward, but
LP. Rice's classic paper from 1959, Radio Transmission into Buildings at
35 and 150 MHz, published in the January 1959 Bell System Technical
Journal still is worthwhile reading. A copy is available at
http://www3.alcatel-lucent.com/bstj/vol38-1959/articles/bstj38-1-197.pdf
-- however, Rice's study considered only commercial type buildings in
the New York City area.
An attic mounted antenna should exhibit less loss than the roughly 10 dB
figure for residential work at 150 MHz since some allowance for interior
walls is included in the 10 dB figure and an attic antenna only looks
through the roof. Some - perhaps nearly all - of this excess loss will
be offset by the increased height of the attic antenna compared with the
same antenna on a ground or second story floor. As a really rough
estimate, doubling the antenna height above ground level yields 6 dB
increase in signal level. There are lots of caveats in this rule, but if
one is doing back of the envelope estimates it's still a useful concept.
Therefore, I would expect, as a rough and ready estimate an antenna at
12 feet above ground in the attic to work about as well as the same
antenna outside at 5 or 6 feet above ground.
Jack K8ZOA
On 8/13/2013 4:42 PM, Ron D'Eau Claire wrote:
Keep in mind that absorption by the walls, roof, etc. increases with
frequency. That's why a microwave oven will heat your dinner but no amount
of 40 meter signal will do a thing for it.
Still, I've had good success with a J-pole in the attic. No weak signal DX
work, but a good local signal.
73, Ron AC7AC
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Mike WA8BXN
Sent: Tuesday, August 13, 2013 11:58 AM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] Antennas in the attic
Remember things are different on VHF/UHF bands. Its often FM which reduces
noise problems to some extent, and the wavelengths are shorter and get out
between conductors a lot better than HF.
73 - Mike WA8BXN
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