So...The screen on this retrofit might not be the best:
http://www.hamradiomarket.com/Articles/Ten%20Tec%20Centurion.htm
Looks a little wide and not to well snugged down.
N9FUT
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Roger (K8RI)
Sent: Wednesday, October 06, 2010 12:48 PM
To: amps@contesting.com
Subject: Re: [Amps] Shielding Effectiveness
It's important to remember that hardware cloth which comes in many
sizes, or screen does not normally give a good contact around the edge.
If fender washers are used they basically need to be edge to edge.
Commercial equipment uses a bracket, or frame to hold the screen in
tight contact with the cover/chassis around the entire periphery.
Although screen can be a much better shield at VHF, that advantage is
lost if that contact is not continuous around the edge.
73
Roger (K8RI)
On 10/6/2010 11:13 AM, Ward Silver wrote:
> Per Ott's "Electromagnetic Compatibility Engineering", section 6.10 -
shielding effectiveness in dB is:
>
> S = 20 log (wavelength / 2xL) where L is the maximum linear dimension of
the aperture.
>
> If you have multiple apertures, such as an array of holes, the general
procedure is to calculate S for one hole and then reduce S as 10 log (n)
where n is the maximum number of holes in a straight line in the array.
>
> For example, if S for one hole is 52 dB (a 2.5 mm hole at 2 meters) and
there are at most 20 holes in a line, S would be reduced by 10 log (20) = 13
dB to S = 52 - 13 = 39 dB.
>
> This is an approximation, of course, plus there are seams and other things
to worry about. But it's a good way to at least compare types of apertures
in shields.
>
> 73, Ward N0AX
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|