Stationmaster MKI not working

[VK7HH]

I've just noticed recently on my Stationmaster MKI that it is way out of tune, and that it used to be much better.

At 29.6 MHz I get a reading of 2:0:1 SWR, then when I first put it up, it was dead flat.

At 28.490, I get 3:0:1, then when I first put it up, which was around 1.5:1.

I've taken it down, changed the feedline, checked the tap off point, resoldered that for any bad connection.

Any ideas?
It's at 7m AGL.

[VK2OMD]

Any ideas?

Hayden,

Ok, I think you have told us that you have checked for bad connections, corrosion, water, s/c etc.

The Stationmaster does nothing to suppress common mode feedline current or current on the supporting mast or structure.

That means that those things are as much a part of the antenna as the tube above the feedpoint, and changes in those conductors or their environment will affect feed point impedance (resonance, VSWR etc).

This might not be a popular explanation or a simple explanation of how the antenna (and other end fed half wave 'ground independent' verticals such as Ringo, J pole etc), but it is a more complete perspective and explains why they are so sensitive to the mast and feedline arrangements.

The operation of these things on lower bands (eg 40m) as is popular with six hour hams irrespective of whether or not the coil is changed is essentially a top fed mast and feedline, the mast and feedline contribute more to the radiated power than the nominal radiator.

Owen

[VK7HH]

Yes,
I've check for corrosion, water etc, all seems fine. I replaced the existing feedline as I believe water got into that. I did wind a small coaxial choke at the base of the antenna to stop any currents flowing on the feedline.

I also think that changing the length of the feedline also contributes, because as you say Owen, the antenna also radiates through the mast and feedline.

Is there any way to perhaps fix this, or just stick with it and use the antenna tuner to make the radio happy

[VK2OMD]

Yes,
I've check for corrosion, water etc, all seems fine. I replaced the existing feedline as I believe water got into that. I did wind a small coaxial choke at the base of the antenna to stop any currents flowing on the feedline.

I also think that changing the length of the feedline also contributes, because as you say Owen, the antenna also radiates through the mast and feedline.

Is there any way to perhaps fix this, or just stick with it and use the antenna tuner to make the radio happy

If you wanted to decouple the mast and feedline, you could use a common mode choke.

Decoupling the mast and feedline will reduce the sensitivity to the configuration of the mast and feedline, but does not standardise the feedpoint impedance. You may still need to adjust the feed point matching if you want the lowest VSWR.

'Fixing' high VSWR with a local ATU is actually fixing the load seen by the tx. It does nothing for the different transmission line loss under mismatched conditions. You could assess the impact of mismatch with TLLC to determine whether it is acceptable. Contrary to popular belief, there are no reliable Rules of Thumb for this, the best answer comes from calculating the actual scenario as is done in TLLC.

Of course, there will be some additional loss in the ATU, but at 10m and low VSWR it should be quite small.

Owen

[VK7HH]

Rehashing an old thread....

What methods for conversion of the MK1 to 28/29MHz have people used?

I have a brand new MK1 to go up in the air that I can shorten, but do I also move the tap up one on the coil?

[VK3KCX]

I had one of these once and it developed a bad joint at the point where the coil was riveted to the vertical radiator. Not much of an antenna, also known as the "Station Disaster"

[ZL2WHO]

I have one of these for 10m and it tunes very well. Its on the ground at the mo so happy to take measurements and send if that is any help.
I devoted a whole day to getting it spot on even to the point where i compressed or spread the coil windings to find the sweet spot.

The only mistake i made was fitting a bung to the bottom of the whip mounting gland. This kept the water in and screwed up the SWR. Removing the bung draining the water brought it back to 1:1

Just ask...

73
Mark.

[VK1KW]

Hello Hayden,

Having checked all above have you moved it recently from where you were getting good SWR? i.e. up higher or another location. May work better just above the gutter than high on a pole. (ground)
Slide the sections in and out and use some WD-40.
Have a good look up inside the connector for animals or arcing marks across the insulator in the connector. Check the pin is not broken in the middle.
Check the lead to the center pin is soldered and clean - give it a good tug. May be a lousy join.
Shouldn't need to move the tap but slide the top section to get perfect SWR - it shouldn't need much.

Hell - they work ok on 6 meters with half of the coil removed, spaced the same and then center tapped.

Cheers

[VK7HH]

Hi,
Thanks for all the replies.

I have converted one to 6M too, and again my MFJ-259 (the first version) analyser read the best SWR to be at 1:6:1 - same as two of my other SM's on 10M.

I couldn't get it any lower.

So I borrowed a HF transceiver from someone yesterday and hooked it up to my Avair SWR meter which correctly says 1:1 at my desired frequency. The MFJ was the problem!

I'm going to do a return loss sweep to double check, but that seems to have fixed the problem. I siliconed around the SO-239 and coil connection tap point.
I could hear several contest stations yesterday on the CQWW contest so it seems to be working to my liking now.

Thanks
Hayden VK7HA