The AM Forum

I am getting my MS2 yagi ready for 6 meter AM and I think there is an error in the tuning chart (attached).
Look at the dimension 51 MHZ "Driven Element Tip Length Non Gamma Side" I think it should be 38 1/4. Thoughts?

Thanks
Carl
WA1KPD

Who is MS2?

Whole chart seems a little strange.   At 50.15mHz both sides are the same.  At 51mHz the difference is 1.5", at 52mHz the difference is 1.25", at 53mHz the difference is 1.0" that seems correct.

Why at 50.15mHz are they the same??  Until you look at the gamma rod settings, 1/8" at 50.15mHz and 3/8" for the other three frequencies, other gamma settings are 7-5/8" and 7-7/8".  Not sure if that has anything to do with it.  Also notice the total driven element length is the same for 50.15mHz and 51.0mHz. Probably the reason for the off center feed.  It gets shorter at the higher frequencies.

Fred

M2 Antenna Systems

I'd venture a guess it's to skew the pattern opposite the skew inherent from a gamma feed.

--Shane
KD6VXI

Looks like it's the 6M-3SS. It looks like an error. Given the ratios indicated, if I was to set it up for 51 MHz, that length would be roughly 38 inches. Unless you plan on operating around 51 MHz or above, I would set the antenna dimensions from the 50.15 MHz column.

I thought of that also, but didn't think it would alter the pattern that much.  A gamma match does result in a off center pattern.  A hair pin or T match produces a more balanced pattern.

Fred

I can understand the difference in lengths, but why an opposite skew on that one freq point? It is not only out of ratio, it is in the complete opposite direction. It increases in length going up in frequency and then at the next frequency point it becomes proportionately (generally speaking) shorter then the first point
I am assuming it is a typo and it should  read about 38".

   

That's correct.

If that dimension really bothers you, call them on Monday.

I don't think it's a typo.  Look at the total length of the driven element at 50.15mHz and at 51.0mHz,  they are the same.  The gamma settings are different for the two frequencies which may have an inherent shortening affect on the driven element.  Plus the skewing is still somewhat not clear.  At the higher frequencies the driven element gets shorter, as it should.

Another thing I see,  the reflector and director get shorter by about 1" for the different frequencies, but the driven gets shorter by a more than two inches for the three upper frequencies.

Like I stated in my first post, the whole chart is strange.  Maybe the 39.25" is wrong, but then the skewing would be out of proportion.  It goes 1.5"-1.25"-1.0".  If you use 38.25" then you would have 0.5"-1.25"-1.0"

That does seem kind of odd Carl. Is this the 6M3 model?

Rob W1AEX

It is Rob.

I sent them this question I have a 6M3S antenna I want to put on 50.400 MHZ. In looking at the tuning chart the length for the Driven Element Non Gamma INCREASES from 38.5" on 50.150 MHZ to 39.25" on 51.00? it then drops to 37.5" inches on 52.00 MHZ. I assume the length for 51.00MHZ is wrong, or is that some sort of engineering oddity?

Here is their official reply:
We do not have dimensions other than what is published and those are only starting points.  They usually are good/close, but every installation is unique.

To tune your antenna for your desired frequency, shorten the driven element until the VSWR dip is centered where you want it, then adjust the gamma match for best VSWR.  Repeat if needed to get the best VSWR.

I have it pretty close and would finish it today, but darn its cold.....
Carl

Ignore what I posted here before about my 6M3 from M2. As Pete indicated it looks like you have the 6M-3SS antenna which is quite different from mine. I certainly agree about being cold. This is not a "beautiful day in the neighborhood" for antenna work in Connecticut!

Rob W1AEX

Hi Rob,
Thank you,
Yours has a T-Match and a balun as well as a slightly longer boom. Mine has a gamma match, no balkun and is actually designed to be broken down for portable use. I picked it up for $75 at a fest. Retail they sell for about the same.

When I get it set I will plot the SWR. It does not seem that different then what you are seeing. I suspect mine is a little sharper.

Its on the back deck now using the umbrella hole and base in the picnic table while I get it ready to move to the roof top which will put it up about 35 ft.
73 OM
Carl

Differences shown below:

Thank you Pete, Interesting to see side by side.
Carl
WA1KPD