High SWR

Jim

Im looking for ideas or suggestions. I am running a 6400 connected to an Ameritron AL-80B amp connected to an LDG AT-1000 Pro 2 tuner connected to a Daiwa CN-901HP power/swr meter, which connects to a Hygain AV680 vertical antenna.  My 6400 does not have the internal tuner. My issue is that the 6400 shows the swr pegged, but the swr at the power/swr meter shows almost 1 to 1.5 after the tuner goes through its gyrations. Everytime I transmit, the tuner wants to go through a tuning cycle. I have eliminated (one at a time) all of the devices listed above, and Ive replaced all of the coax jumpers. Nothing changes. This same condition exists on all bands except 40 meters, which the radio shows a 1.75 to 1 swr and the tuner acts normally. Im at a loss as to what to try next. I would appreciate any ideas as to what to try next. Thanks in advance KC3KRZ

KD0RC

Some amps have an input network adjustment that allows you to match the rig to the amp so to speak.  Does the AL-80B have a series of holes on the back labeled with the band names?  If so, I think you can put a non-conductive screwdriver in there and adjust each band.  You will want to follow the Ameritron instructions on that before you turn the adjusting screws.
73,
Len, KD0RC

Neil D Friedman N3DF

Shouldn't the SWR meter go between the amp and the tuner rather than between the antenna and the tuner?

Homer1952

1. What happens when you replace the antenna system (coax/Hygain) with a dummy load?
2. Do you have an antenna analyzer?

-Bob W8RMV

Bill -VA3WTB

Neil has a point. Your SWR meter right now is seeing the antenna SWR. But if you put the SWR meter behind the tuner, it will tell you the SWR that the tuner provides.

RoyS

Neil, unless Jim's post is a typo, I think you nailed it.

Bill -VA3WTB

So I would do this.

Radio> SWR meter> Amp> Tuner.

Geoff AB6BT

That will only tell you the SWR from the radio to the amp, not how well the amp is matched to the antenna.

Yes?

KD0RC

Yes, but that might be the problem.  If the amp is not providing a 50 ohm load to the exciter, Bill's set up will detect that issue.  Once resolved, I agree, the final point should be:
Radio - amp - SWR meter (assuming it can handle the power...) - tuner - antenna

Len

Bill -VA3WTB

KD0C, that would be correct, now he can see how everything is behind the tuner. But for tuning the in puts you use a dummy load on the amp and tune for max power. I don't think his amp has them,,but my AL 811 does for all bands.

Doug

It seems like the tuner might be at fault here. Once it reaches a satisfactory swr I wouldn't think it would continue to start another tuning cycle. Is there a way to configure the tuner so once tuned it will not start up again unless the frequency is changed. It is either that or the load is breaking down like someone mentioned you might try a dummy load. If there is a way to shut power off from the tuner once it tunes the vertical and then if the swr is high I would say the vertical is breaking down.

And yes that amp does have a way to tune the tune input per band or my 80B does.

Geoff AB6BT

I think this is the correct approach as well.

Perhaps the first step would be connect the radio directly to a 50 Ohm dummy load ave verify that there is a good match. 

If that looks good then proceed to the next step.

There may well be a problem with the amp input. If the SWR, measured between the radio and the amp with the amp connected to a dummy load of 50 Ohms, is high then you will have isolated the problem and can look a bit deeper as to the cause.

Jim

Thanks for the tips.  I will investigate and report back

N8AUM

Lots of good suggestions, 1st is dummy load ON radio to verify that it reads correctly as Geoff suggested and if you have 2, place them in parallel and see if it shows correctly.  
Good luck !

RoyS

KC3KRZ, Jim. I have some history with the Ameritron amps. However, mine was with the Ameritron AL-811. Although it is a different amp, it has the same input pi-network as your AL-80B. I also have experience with the Flex radio. In this case it was the Flex 6500.

To make a long story short, After receiving my AL-811 I followed the instructions on how to tune the pi-network. I had success except on the dual (10/12, 15/17 and 20/30) tuning slugs. I never was able to get more than half power out of the amp on 10, 12, 15, & 17. In my attempts to adjust the 10/12 slug, I finally destroyed it. I was never able to get the SWR on the radio below 1.3:1 which caused the radio to fold back on the output power. Out of frustration, I went into the amp and by-passed the network completely. I then hooked a LDG-100 auto tuner between the radio and the amp.That solved my matching problem and made the radio happy no matter what band I was on. The amp was also happy and would put out about 90% of the rated power (600W) on the high bands.

My whole point is: do not be surprised if you have problems striking a balance of tuning on the dual tuning slugs. Use care with your tuning tool and above all, make the SWR on the radio as low as possible. 

Jim

OK  here is the status...… first of all I typo'd when I listed the sequence of devices, it is 6400 to amp toto swr meter to tuner to antenna.  I cabled the radio into a dummy load and the swr is nil, so in my mind that eliminates the radio as a problem. next I jumpered over the amp, eliminating it from the rf path. No improvement in swr. I replaced  the swr meter with a different one. No improvement. I don't have a substitute tuner to swap out. Ive already replaced all the coax jumpers with brand new ones. Correct me if im wrong, but that leaves only three possibilities...…… the tuner, the outside coax leading to the antenna (lm400flex less than 6 moths old) or the antenna itself. Any other ideas?
By the way.  thanks everyone for the help  KC3KRZ

Bill -VA3WTB

What SWR do you have going directly to the Flex, bypassing everything,,work backwords till you find were the high SWR begins 

KI4P

at a 1.3 the flex should have never folded back on that, there usually good to upwards above 2 from what ive read.jmo!

RoyS

KI4P.
The threshold for SWR power foldback was set at 1.2 several years ago. After many complaints, the newer radios are able to handle a higher SWR so the software was changed to take advantage of the improvement. (at least that is what I understand)

Roy - W5TKZ 

KI4P

Wow! 1.2! That's crazy. Hadn't heard that one

Neil D Friedman N3DF

The 6400M/6600M manual says that software folds back the transmitter power if the reflected power exceeds 25 watts.  That's an SWR a lot higher than 1.3:1.

RoyS

Neil, you will get no argument from me on that one. I just referenced the original post from Jim that states "the 6400 shows the swr pegged" so no telling what the actual SWR is.

Cono A DelRosso

I have the exact same setup 6400M LDG AT1000PROII With the M-1000 Meter and the AL-80B AMP on 20m 14.290 the FLEX SWR shows 2.5 but the tuner shows me 1.5 but if I tune the AMP on the FLEX is a perfect match.

Bob Needleman

If you find, as Bill suggests, that the SWR going directly to the Flex (bypassing the tuner) is <2:1, and then when you insert the Amp inline the SWR measures high (>2.5:1) then the likely culprit is the tuned input circuit of the amp. There is a procedure on how to adjust the pi network tuned input circuit of the AL-80b, and you should be able to find that in your amp manual or online. GL/73,
Bob k3AC