[RFI] Which filter to use?

Mon Apr 4 13:01:45 PDT 2011

You must remember that filters can only eliminate what you transmit.  Even
if the filter works perfectly there are still at least 5 sources of problems
that you can not fix with a filter on your station:

1. rectification outside the station, anything near the antenna (or a bad
antenna joint) that conducts and is dirty can cause this.  Metal gutters,
metal roofs or roof edging, power lines, phone lines, ground wires, fences,
the tv antenna itself, etc, etc, etc.  This is the hardest to find and fix,
it can be anywhere but usually close to the transmitter.

2. front end overload of the receiver.  This causes the receiver to
interfere with itself.  Try a high pass filter on the receiver to reduce
this problem. And check for good grounds and shielded cable.

3. mixing with some other signal.  If there is a nearby transmitter like an
FM broadcast station the combination may be enough to either cause mixing
from rectification or front end overload.  

4. power line input.  Your signal can get into the receiver on the power
line.  This can be helped by adding proper grounding and filters on the
power line of the receiver.  It is made worse if your antenna is low or
close to the power lines (don't forget the wires inside the walls).

5. direct overload of receiver internals, if the case of the receiver is not
shielded you can overload internal circuits directly causing problems that
won't be fixed with either high pass filters or grounding.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: Eduardo Somoano C [mailto:co8ly at frcscu.ciges.inf.cu] 
> Sent: Monday, April 04, 2011 23:37
> To: doc at kd4e.com; RFI List
> Subject: Re: [RFI] Which filter to use?
> Dear friend David
> I use the Drake TV-1000 and I built several filters that I found Web,
> regrettably with
> none could eliminate the ITV in the Channel 2 when I transmit 
> in 20, 10 and
> 6mtrs.
> My opinion is that any form doesn't exist of eliminating ITV 
> for harmonic in
> the channel 2.
> If somebody says the opposite that demonstrates it to me with 
> facts....
> hihihihi.
> Strong hug.  73.-
> Eduardo. CO8LY
> Santiago de Cuba .- Cuba
> ----- Original Message -----
> From: <doc at kd4e.com>
> To: "RFI List" <rfi at contesting.com>
> Sent: Monday, April 04, 2011 12:35 PM
> Subject: [RFI] Which filter to use?
> Has anyone swept these filters?
> I'm considering their use on the output of a broadband 1.5KW
> PEP/750W CW 160-6M solid state amp to knock-down harmonics.
> Drake TV-1000-LP 30MHz 1KW  (17, 15, 12M)
> Nye Viking Model 020-001  (10M, 6M)
> [HF Low Pass Filter.  Rated at 3 KW continuous, all mode,
> 5 KW peak.  FLAT, low loss, passband and stopband with over
> 65dB attenuation above 57 MHz.]
> Or, are there specific alternative products you can recommend
> for this application, please?
> Thanks!
> --
> Thanks! & 73, KD4E
> David Colburn http://kd4e.com
> SE-GA Tailgate - April 9th, 2011
> Have an http://ultrafidian.com day
> I don't google I SEARCH! http://ixquick.com
> Shop Freedom-Friendly http://kd4e.com/of.html
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi

More information about the RFI mailing list