The only experience I have is with the Mini-Circuits low pass filters at the receiver input. They got us out of the woods on two sites. One of the sites had a TV transmitter the other had some sort of sweeping radar. If their curves can believed it would help in many situations. As you say "no one filter does it all".
Gran K6RIF
At 06:08 PM 11/14/2003, you wrote:
From: Gran Clark <[EMAIL PROTECTED]>
>
>Hi Bob;
>
>Great hard data!
>
>It also shows the need for a low pass filter in front of your receiver on
>high level sites.
>
>Gran K6RIF
I (slightly) disagree for 2 reasons:
1. A low-pass filter, depending on the design, can also be subject to spurious responses well above the cutoff freq., though they will probably be many more times above Fc than they will be above Fo for the pass cavity.
2. The spurious passbands of the pass cavity are quite narrow below 2.5 GHz, or ~5 x Fo. For a UHF cavity, the chances of anything significant being within those spurious passes is very low. Now for VHF, things could get a little dicey because if all the spurious responses scaled down to a similar 2 meter pass cavity (like the 11" diameter Motorola 1/4 wave can), the responses falling around the 3/4 wavelength region would fall somewhere in the (crowded) 420-512 MHz range.
My point in all this is that no ONE filter will be perfect. However, 2 can be. If you use 2 pass cavities of DIFFERENT design, it may be possible to get the spurious passes of each cancelled by the other. The low-pass filter idea would achieve the same result, but it offers no additional in-band pass filtering.
Bob NO6B
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