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Author Topic: Higher SWR with Bencher YA-1 Low Pass filter. What gives?  (Read 2163 times)
W6UX
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« on: January 26, 2012, 03:24:40 PM »

I am getting a noticeably higher SWR reading (sometimes > 3:1) indicated on my K3 when using a Bencher YA-1 Low Pass filter.  In some cases, my K3 gives me a HIGH CURRENT warning.

Taking the filter out of the loop immediately reduces the SWR (only 1 bar of SWR on the K3's SWR meter, or about 1.1:1).  The antenna is a Traffie Hex Beam which I previously confirmed had low SWR across its operating spectrum.  I am bypassing my internal tuner, as one should not be required with this antenna.

Can anyone advise me on whether the Low Pass filter is defective, or if this is a trade off of using one?  What other kinds of tests might I conduct to further identify the culprit?

I tested with two jumpers, one RG8X, the other LMR400 Flex, but both showed the same increased SWR reading.

Thanks for any and all comments!

-Jeff
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WB6BYU
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« Reply #1 on: January 26, 2012, 03:40:45 PM »

There are two likely possibilities.

First, that the filter is somehow bad or out of adjustment.

Second, that your rig has a high harmonic or other spurious output.  When you
transmit into a dummy load the harmonics are terminated and the SWR is low on
all frequencies, but when you transmit into a high pass filter the SWR for the
harmonics will be high.  The SWR meter is not frequency selective, so will show
total reflected power regardless of what frequency is being reflected.

Do you see this behavior on all bands, or just the higher ones?  Is it the same
when the filter is terminated in a dummy load?  What happens if your reverse
the connections to the filter?
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W6UX
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« Reply #2 on: January 26, 2012, 03:51:26 PM »

I'll run a series of tests on each band (low, mid, and high end of the phone spectrums), with and without the filter, and will try both ends of the filter.  I'll post the results when I have them.
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W6UX
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« Reply #3 on: January 26, 2012, 05:11:17 PM »

Well this is really interesting:

BandNo FilterInput (R)Input (L)Dummy load
28.3181.0:11.0:11.0:11.0:1
28.4501.0:11.1:11.1:11.0:1
28.5501.2:11.3:11.3:11.0:1
24.9301.4:11.4:11.4:11.0:1
24.9401.3:11.4:11.4:11.0:1
24.9871.0:11.3:11.3:11.0:1
21.2001.0:11.0:11.0:11.0:1
21.3251.0:11.0:11.0:11.0:1
21.4471.0:11.0:11.0:11.0:1
21.4471.0:11.0:11.0:11.0:1
21.4471.0:11.0:11.0:11.0:1
21.4471.0:11.0:11.0:11.0:1
18.1101.0:11.0:11.0:11.0:1
18.1451.0:11.0:11.0:11.0:1
18.1651.0:11.0:11.0:11.0:1
14.1501.2:11.3:11.3:11.0:1
14.2501.1:11.3:11.3:11.0:1
14.3471.0:11.0:11.1:11.0:1


These readings were taken using the K3's internal SWR measuring function (10 watts output).  These numbers actually look very good.  What I don't understand is why I got a HI CURRENT/HIGH SWR warning from the K3 last night operating SSB on 28.375.  I also saw a HI CURRENT message from the K3 the previous day operating 14.080 RTTY.

The frequencies where SWR was a bit lower are highlighted in bold.

Next time I see a high current warning message I'll check the SWR using the K3's SWR measuring function.  I guess I jumped the gun thinking SWR was over 3 (I was testing with my voice, not a tone).

Maybe it's different at 100 watts output; I'll check to see if I can get the K3 to measure SWR with 100 watts out.  Anyone have anything to add here?

Thanks,

Jeff
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KI4SDY
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« Reply #4 on: January 26, 2012, 05:49:54 PM »

Maybe you didn't have the connectors screwed on all the way and flush with the assembly?  Huh
Did you install the connectors on the cable and the jumpers or did you buy them already installed?  Huh

Use a volt/ohm meter set on continuity to check the connections on the jumpers first and then your main coax cable disconnected from the antenna. The cable should show "open" when the shield is tested to the center connector to the shield and closed when testing center to center and shield to shield. While testing them, move them around to see if you get intermittent contact. Jumpers are always suspect in a feedline problem!  Wink

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W6UX
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« Reply #5 on: January 26, 2012, 06:32:16 PM »

Maybe you didn't have the connectors screwed on all the way and flush with the assembly?  Huh
Did you install the connectors on the cable and the jumpers or did you buy them already installed?  Huh

Use a volt/ohm meter set on continuity to check the connections on the jumpers first and then your main coax cable disconnected from the antenna. The cable should show "open" when the shield is tested to the center connector to the shield and closed when testing center to center and shield to shield. While testing them, move them around to see if you get intermittent contact. Jumpers are always suspect in a feedline problem!  Wink

These jumpers were purchased (RG8X at a swap meet; LMR400 from the DX store).  Yeah I'll double check these!
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NO9E
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Posts: 405




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« Reply #6 on: January 27, 2012, 10:15:11 AM »

SWR meter in K3 is not very accurate. Sometimes it gives 1.0 readings when LP100A and other meters indicate 1.8.

I also have the same filter and it changes SWR by up to 0.4. I just ignore it when I can. Also with a tube amp a slight bump in SWR is unimportant.

Was the problem on 10 or 12m? My K3 at one time had a run out on 10m when on full power. I have heard about this problem from other K3 owners. Probably fixed some 2 years ago. 

One big question is why to keep the filter. It was important with TV channels around 50 MHz but now the filter may serve no value.

Ignacy, NO9E

These readings were taken using the K3's internal SWR measuring function (10 watts output).  These numbers actually look very good.  What I don't understand is why I got a HI CURRENT/HIGH SWR warning from the K3 last night operating SSB on 28.375.  I also saw a HI CURRENT message from the K3 the previous day operating 14.080 RTTY.
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