[SCCC] Bandpass filters

Timothy Coker n6win at yahoo.com
Sat Jun 30 16:37:03 EDT 2018

 I've been going through a lot of what might be plaguing you Bob. The previous member's replies are correct... however, as Joe points out there may not only be leakage through your braid, connections, switches, etc... but there may also be external rectification issues that are site dependent. As Bob, NC6Q says, if you have a need for additional inter-station interference resolution, you may well gain benefit from stacking multiple bandpass filters (and/or coaxial stubs) in different segments of your coax's TX-Ant chain.
My experience in buying new 4O3A high power band pass filters (generally considered only rivaled by Pavel VA6AM's offerings on a commercial basis) is that they helped immensely over previous use of W3NQN 3 pole, ICE 419a's, and coaxial stubs. However, not all of my interference issues dissipated. So I've experimented with adding W3NQN and/or coaxial stubs to go along with the 4O3A equipment.
After bypassing every item conceivable as W2VJN describes in his book on this subject, talking to K6AM, K6ZZ, K6LA, W6YI, etc about their own experiences to go with countless suggestions from other contesting hams on other reflectors, I've been able to absolutely find that the high quality 4O3A's are doing all they are supposed to and my station is suffering from external rectification issues that won't be solved by additional bandpass or stub filtering.
That being said... try stacking... it helped when I had only the lower quality filters and stubs on hand. It may well help when someone is only using a set of stubs, Ice, Dunestars, or NQN's (in order of seeming effectiveness and correlated economic cost).
Other things, as K9YC writes about, to check on is your grounding and external situation. Good coax (hardline being best for shielding and cross talk), great grounding implementation, external AC issues (like walwarts and other power supplies (that solved my TX20/RX15 issue erasing 30+ dB of head scratching interference)). He found that they were able to eliminate all of their current interference one FD with good grounding practices... only to find the exact same mobile setup was all messed up when they changed sites. 

Years back, both K6AM and K6ZZ alerted me to watch for external dissimilar metal junctions re-radiating a TX signal directly into the pass band of another band's BPF as a diode rectification scenario, etc... that's been also reported by ham's on CQ-Contest having found that metal rain gutters and metal roofs were the culprits of seemingly unexplained interference that any amount of stubs and/or BPF's couldn't quell.
At the end of the day (more than one most likely) you may very well find that some interference is outside of your sphere of control... but at least for me that recognition has helped me not invest more money into filtering when my problem has been verified to actually be something else.
Try stacking the filters and/or stubs, rule that out... if that doesn't help its time to hit the books some more and start sniffing out problems, assuming it's important enough to your operation.
Tim / N6WIN.

    On Friday, June 29, 2018, 7:49:17 PM PDT, Marty Woll <n6vi at socal.rr.com> wrote:  
 Hi, Bob.

We just used a set this past Field Day weekend (operating at the 100-Watt
level) and found one per band to be quite adequate.  There was zero
inter-station interference.  

If, for some reason, you need or want to "stack" them, you might experiment
with spacing them out along the coax.


Marty N6VI

-----Original Message-----
From: SCCC [mailto:sccc-bounces at contesting.com] On Behalf Of Bob Grubic
Sent: Friday, June 29, 2018 6:32 PM
To: Southern California Contest Club
Subject: [SCCC] Bandpass filters

Has anyone heard of using *two* of the same bandpass filters in series for
any benefit?

For example, using two 20 meter bandpass filters inline? Say for Field Day?
Any benefit to doing that?

Bob NC6Q
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