Topband: Bandpass filters for receive antennas

Jim Brown jim at audiosystemsgroup.com
Mon Aug 31 12:43:12 EDT 2015


On Mon,8/31/2015 4:37 AM, Larry via Topband wrote:
> I have been following the discussion on front end relays with 
> interest, and I was wondering
> what sorts of bandpass filters folks are using for receive antennas.

Bandpass filters do nothing for in-band signals -- their only function 
is to reject OUT OF BAND signals. The primary reason for using bandpass 
filters IS for RX. A good 160M bandpass filter would be effective at 
reducing overload from AM broadcast stations. So would a high pass 
filter. There is a survey of bandpass filters for contesting at this 
link. http://k9yc.com/BandpassFilterSurvey.pdf

Most bandpass filters are designed for low power -- 200W or less, and 
some for only 100W. This means that they must be installed between the 
rig and the power amp, so they are of no help with killing harmonics 
generated in the power amp. This is a great application for stubs -- if 
placed after the power amp, they can significantly reduce the level of 
harmonics. Here's an applications note that appears in the most recent 
National Contest Journal. http://k9yc.com/LocatingStubs.pdf

73, Jim K9YC




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