The AM Forum

I just got a working Valiant in my collection, and I am having an issue that I am simply uneducated about.   I have a MFJ 267 watt/SWR meter inline with my antenna, a Windom up 45 feet that tunes fine with my Viking 1, and any modern rig tuner.... the SWR is generally under 4:1 on 75 meters normally.

Anyhow, tuning around today on 75 and 20 meters, I can't seem to get the rig tuned properly.  It will develop full power according to the meter, and I have tested it on the dummy load too, and it's fine.    What I can't seem to figure out is why the meter pegs on reflected power.   This Valiant has NOT been connected with a 3 wire plug, still using the 2 wire fused plug (in great shape), and I haven't hooked it to any ground.   

My question would be, do you think the lack of proper grounding wire is causing this issue.  I have plans to convert to a 3 wire cord/plug soon anyhow, but just wondering what might be the issue.   

I am feeling kind of dumb.    The Ranger tunes fine on this band as well, just curious if I am missing something else.... never used a Valiant before, so a bit of a learning curve for tuning it properly anyhow.   Thanks,
Joe  AB5OR

Does the meter (reflected power) peg when its on the Dummy load too?

If it does, something is amiss in your metering circuit.

Is it possible you have the Valiant tuned to a harmonic?   Or could the bandswitch have slipped?

73
Ted  W8IXY

Does not peg when on Dummy load.    180 watts output, zero reflected....   Bandswitch.... I think it's ok.

I zero beated with know frequency in receiver.... now, tuned to a harmonic, I don't think so, but it's possible.

The radio has nothing to do with reflected power as measured by an external meter.  The problem can only be in; the meter; feedline or antenna.

4:1 SWR is really too high in any case, radio notwithstanding.

73DG

The only logical explination to this is the one that was offered. You might have tuned the valiant on a harmonic.  When into the dummy load, the dummy excepts the harmonic.  When into the antenna, The antenna does not except or radiate the harmonic and sends it back.

I think most of us have all had issues with Dowkeys over the years.  Are you using one?

Well, might not have been clear.   My ft107, ranger, and Viking 1 can tune the same frequency to roughly 2:1 or better, with no external tuner. So I figured the valiant should do the same.   Is this correct?

I have three valiants.  Load the rig BY the book into the dummy. Note the plate current. Should be around 300MA at 150 watts carrier or so.  Then use the modern rig to tune your antenna tuner flat.  Switch the valiant inline.  The Plate current should be the same. This would indicate that you are still loaded into 50 ohms.  Can you try that? 

If the plate current is of, tune the tuner slightly to get back to 300MA.  If this does not work, then swap the coax cable and or dowkey. 

After that, i really do not know what could be wrong unless you are tuning that Driver stage on a harmonic. Never trust the knob postion. The knobs have been off sometime in the last 50 years.
C

Excellent ideas and I will do exactly that... And let you know.

Progress!   

Ok, so I bypassed the relay and went straight antenna coax into meter to valiant.   I can tune it to 2:1 and 150 watts out on 330 ma of current, so radio and antenna must be fine.   It's got to be relay box or coax feeding it!    Thanks to all!

Tune what to 2:1?

My wattmeter is showing a 2:1 swr match radio to antenna.   

OK. Looks like you found the problem.

Just to be clear, the antenna SWR is what it is totally independent of any radio you connect to it. You aren't tuning it or changing the SWR by tuning and loading up the transmitter. You have shown that the Viking and the Valiant will tune up just fine with a 2:1 SWR, so there is no need to mess with a tuner.

Have fun.

Unless the generator is tuned to a harmonic.

I said it was independent of the radio. The SWR is obviously not independent of the frequency.   ;D

That is an excellent and correct point.  The reason it is a little high is because one end of my antenna is too close to ground, but it will be raised soon where it used to be and will lower the swr of the antenna and should make my pi network tune even better.   My original problem is something inside my relay box....  Time to look and see what I see.

Glad you found the trouble maker relay....
And 4:1 SWR is nothing at Valiant power levels, even using coax. Getting close to 10M freqs starts to be a concern for losses.
Broadcasters have serious problems at their power levels with high SWR.

I had a very weird situation on my Dentron 3KA. At 1885, high SWR, and a lot of RFI in the shack, using the forward/reverse power sensor that drives the front panel meters. Putting RF directly into the tuner and bypassing the RF pickup and the problem is gone.

I noticed it's easy to tune to a harmonic on my Viking II if I'm coming from a higher band.  It's easy to just crank the final (large spinner knob) counter clockwise from the position of the higher band and the first dip can be a harmonic rather than the actual target.   Make sure you have your starting value from the manual for the final loading.  THEN find your dip!

  Had the same problem with my B&W 6100, there were two doorknob caps (1000pf 5kv) one at the input of the plate choke and the other on top of the plate choke. One was cracked and this caused a 3:1 swr everywhere and I couldn't tune it at all. Once replaced the thing tuned FB and it works great. Regards, Richy N2ZD

Well I would be concerned about the losses in the coax at that SWR, not to mention the tuners normal losses.

Coax losses alone at that SWR are about 1.3db at 29mHz with RG-8 types at 100'. If your using RG-8X its closer to 2.9db. That would equate to about 112W and 76W respectively at the feedpoint just in coax losses.

Now add about half a db of loss from the tuner, and ground losses from your Windom & it's balun ... it all adds up. Your 150w transmitter could be losing 50% of its power before it ever gets it to the radiators.

My advice if your gonna go out there and rehang the antenna anyway ... ditch the Windom, ditch the coax. Buy a Johnson Balanced Matchbox tuner (goes with the rig real nice  ;D), get some ladder-line and put up a random length dipole (as long and as high as you can) fed directly with the ladder-line. You will get back about 2db in losses and save most your lost power. I think at 100' length 450ohm window line would be about 0.3db loss under the same conditions. That's 140W of power. And there is little change in feedline losses between 80m through 10m.

It would be the equivalent, in terms of losses, as using Heliax LDF6-50a hardline or close to. And it's a hellava better radiator as a multi-band antenna than any coax fed Windom.

John, W2WDX

If I am not mistaken, there is a chart in the Viking manual showing relative knob setting for specific frequencies on each band.  If you tune and any of the settings are significantly different, then you are, most likely, on a harmonic. 

Lots of  people received letters from authorities back in the 50s and 60s for just that, especially transmitting on 15 when they meant to be on 40.    Be sure the knobs are on the shaft correctly and if you tune much outside the settings, then most likely something is wrong.