Coax Stub Filters

11/04/10 —  Installed the final 2 coax filter stubs:  a CS-1 on 80m and a CS-9 for 160m.  Here’s what the installation looks like in the antenna switching shed.

Coax Stub Filters installed at SixPack on antenna ports:

    * 10 meters – CS-6 (1/2 WL-open 10m) & CS-4 (1/2 WL-open 20m)

    * 15 meters – CS-3 (1/4 WL-shorted 40m)

    * 20 meters – CS-4 (1/2 WL-open 20m) & CS-5 (1/4 WL-shorted 20m)

    * 40 meters – CS-3 (1/4 WL-shorted 40m) & CS-7 (1/2 WL-shorted 15m)

    * 80 meters – CS-1 (1/4 WL-shorted 80m)

    * 160 meters – CS-9 (1/4 VL-shorted 160m)  

10/23/10 — More work on stub filters.  Added CS-3 and CS-7 to 40 meters.

Tested to determine cross-band interference.  I used the lower C51XR for all 10, 15, 20 & 40 tests, and used both the 80m shunt tower and the 80m dipole on both transmit & receive.  Transmit mode CW, power out 1.5kW. Receive mode CW, filters 6.0kHz.

Here is the matrix:  

 LEFT RADIO TX BAND     
RIGHT RADIO RX BAND1015204080160
10X<S0<S0, avoid harmonic>S9+50<S0, avoid harmonic>S8nilnil
15nilX<S0, avoid harmonic>S8nil, avoid harmonic>S9nilnil
20nilnilXnil, avoid harmonic>S9nilnil
40nilnilnilXnil, avoid harmonicnil
80nilnilnilnilX<S3, avoid harmonic >S9+20
160nilnilnilnilnilX

These results pleased me for first attempts at coax stub filters.

10/19/10 — Continued working on stub filters.  Added CS-5 to 20 meters, and installed CS-6 & CS-4 to 10 meters.

10/16/10 — Found burnt barrel connector in top 20m antenna feedline (it had to be 120 feet off the ground).  Replaced it and corrected the intermittent high SWR on that antenna.

10/06/10 — Tilted over Tower #3 and realigned the cubical quad to correct its heading.  It slipped on the mast during a storm last year.

09/29/10 — Began building and implementing coax stub filters on the output of SixPack #1 to Tower #1.  I have MUCH to learn in this area.  Using an AIM4170, I cut two pieces of RG-213 to 1/4 WL at 7.150 MHz.  One I made into a CS-3 and installed on the 15 meter port of the SixPack, and the other I made into a CS-4 and installed on the 20 meter port of the SixPack.

For reference, I’m using Managing Interstation Interference 2nd edition by W2VJN as well as K1TTT’s online Technical Reference and his online copy of K2TR Coax Stub filters article.  I used the K2TR drawing, and cross-referenced it to the table on page 46 of Managing Interstation Interference .  Here is the drawing, with the notations from page 46 superimposed.

Now I have to get more RG-213, more UHF ‘tees’, and spend more time learning and tweaking!

Another good source of info is “Some Q&A About Coax and Stubs for Your HF Station
By Jim Brown K9YC

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