[Elecraft] Antennas in the attic

[Jack Smith]

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-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Mike WA8BXN
> Sent: Tuesday, August 13, 2013 11:58 AM
> To: elecraft at 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
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>