Tuner Genius Tuning unexpectedly changes

David,

I guess I spoke too soon. Here's the problem. If slice A, ANT1 is selected as the transmit channel and an OCFD physical antenna is selected via the AG and the transceiver is operated on 20m, per your instructions, I can set tuning solutions across the entire 20m band.

Then, if SLICE A ANT1 is still the transmit channel but it is changed to 40m and a physical vertical antenna is selected. I can easily find a tuning solution for that configuration, too.

But, when I operate SO2R, I can't put one antenna on Slice A, ANT1 and the other on slice B ANT2 (appropriately selected via AG) because the antenna that was tuned on ANT1 is not tuned when it is attached to ANT2.

I can set both slices to ANT1 and then set one slice to 20m and the other to 40m. This seems to work, but it means that both bands must share the same physical antenna.

That can't be right, is it?

Regards,

Jim Charlton AD0AB I'm sorry to be such a pest.

Hi Dave,

Thanks again for your help. I was following your instructions and, while doing so, I think I found the root of my problem. The impedance presented to the tuner of any of my antennas is slightly different depending on which output it is connected to.

It turns out that the coax cables running from the tuner to the AG are same lengths, but the cables I used to wind my homemade CM chokes aren't. The effect is that the same antenna presents a different impedance to the tuner depending on whether it is being connected by the longer (A output) or shorter (B output) cable.

I checked this by removing all CM chokes so the cables between the AG and the tuner were the same length and the problem disappeared (I hope). I tune an antenna on slice A ANT1,1 output A and then switch the same antenna to slice B ANT2,2 output B and the Tuning solution still works.

I haven't tried all antennas on all bands, yet. So there may still be a glitch, but so far so good.

Unfortunately, without the chokes my dreaded CM current has returned.

Thanks again for your help and I'll let you know if anything different or new shows up.

Regards,

Jim Charlton AD0AB

Hi Mike,

Thank you for your interest in my adventure with my new AG.

My antenna setup consists of 7 antennas connected to the AG. They are: 160m dipole, ground mounted trapped vertical (Hustler 6BTV), 134’ off-center fed dipole, 10/15M EW-radiating fan dipole, 10/15m NS radiating fan dipole, 12/17M dipole and a dummy load. Except for the vertical, they are all homemade wire antennas strung in trees. That means that none is exactly horizontal nor runs in a straight line. The highest point of any of them is about 25-30’ as they must not be visible from the street. All are connected via 50 ohm coax feedlines to ports on the AG. Most of the time they are mismatched to the coax so there is reflected power and standing waves. That’s why I have a tuner.

The asymmetry of the antennas as well as the fact that the OCFD runs right over the top of my house resulted in high CM current getting into my rig and causing it to behave badly.

Before I installed the Flex AG, I had a different 2X8 port switch that connected two of the antennas to two slices on my 6600M. The switch was connected to the tuner via two 30’ coax cables – one for each slice.

In order to suppress the high CM current, I installed CM chokes at each end of the two 30’ coax cables. I also installed a number of chokes on power supply and data cables, but they are not part of this issue.

Three of the four chokes installed on the 30’ cables are homemade. I made them by winding whatever coax jumpers I had through ferrite toroids (mix 31). Consequently, each has a different length of coax wound on its toroid (Hint, this is where I believe the problem lies.). Although this system worked, I replaced the switch because it could not be viewed or operated remotely.

Enter my new Flex AG. I connected it up exactly the same as the previous switch. That is, slice 1 on the radio always corresponds to ANT1 and to Output A on the amp, tuner and AG. Likewise, slice 2 corresponds to ANT 2 and B Outputs.

When the tuner was trained on a particular antenna that was connected through AG Output A to the rig, it worked fine. But, when that same antenna was switched to Output B, the tuning solution no longer worked and high SWR was observed between the tuner and the amp. Retraining the tuner on Output B solved the problem, but then it didn’t work on Output A. It seemed to me that the tuner was seeing two different impedances depending on which output the antenna was connected to.

That was weird because in both cases the antenna was the same, the cable was the same, the mismatch between the cable and the antenna was resulting in the same reflected power on the feedline to the antenna. So, why didn’t the same tuning solution work for both outputs? I believe I’ve traced the problem to the 30’ cables that are not actually the same length.

While the inductance of the CM chokes has no effect on the antenna’s impedance, they do affect the impedance presented to the tuner. That’s because the varying lengths of cable used to wind the chokes adds to, and changes, the effective lengths of the cables between the AG and the tuner. Because the different lengths of cable transform the antenna's impedance differently, the two ports see different impedances for the same antenna.

Since the tuner seems to use the same tuning solution for a given antenna regardless of the output (A or B) it’s connected to, training performed on Output A is not effective on Output B because the two impedances are different.

I sort of verified this by removing the chokes. With only the two 30’ cables between the AG and the tuner the problem was greatly reduced.

This is my current analysis. I’m still experimenting so I may discover that it’s not correct.

Of course, the CM current is back. But that’s a different issue.

Thanks for your interest and help. You Flex guys are the best!

Regards,

Jim Charlton AD0AB