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Re: [VHFcontesting] Tech Help needed

To: peter h <n6ze@aol.com>, "Paulrollinson@sbcglobal.net" <Paulrollinson@sbcglobal.net>, "vhfcontesting@contesting.com" <vhfcontesting@contesting.com>
Subject: Re: [VHFcontesting] Tech Help needed
From: David Olean <k1whs@metrocast.net>
Date: Sat, 2 Jan 2021 11:42:26 -0500
List-post: <mailto:vhfcontesting@contesting.com>
I think the problem is that the Q of the antenna is so high that the elements cannot supply a reasonable reactance at the FT-8 frequency for the matching section to work with. The solution is to try to tweak the driven element or maybe director #1 to raise frequency a bit.  After all, if the elements are not resonant, then no amount of adjustment of the T match or any other type of matching system, will have any effect. I have not played with a 6M7, but do note that director #1 is quite important in coupling into a resonant set of elements.  As you get farther away from the driven element, the element dimensions are less important.One way to try a change is to drill and tap the element end so that you can add more metal if trimming the element shorter does not give you what you want. A small machine screw can add element length.

Dave K1WHS

On 1/2/2021 9:48 AM, peter h via VHFcontesting wrote:
0645 pst 02jan2021
Perhaps contacting M2 directly, with a cc to K6MYC might provide the needed 
bt73Pete, N6ZE in DM04ne with an older 6M7 also

-----Original Message-----
From: Paul Rollinson <Paulrollinson@sbcglobal.net>
To: 'VHF Contesting Reflector' <vhfcontesting@contesting.com>
Sent: Sat, Jan 2, 2021 7:02 am
Subject: [VHFcontesting] Tech Help needed

Good morning all,

I hope you had a nice holiday.

Part of prepping for the January contest included taking down the stack ofM2
6M7antennas and tuning them a bit higher to accommodate FT8/4 frequencies
where the swr runs close to 2:1

After several hours of tweaking we were unsuccessful in elevating the
frequencies. Moving the shorting bars had little effect and the elements are
crimped together so shortening them would be permanent; I prefer not to do

After diving thru the specs, the antennas are 6M7 and not the modern
versions 6M7JHV. Below is a link to the manual.


I'm looking for advice. The manual states that moving the shoring bars out
will increase the tuned frequency (which doesn't make sense to me). If this
is true, I may experiment with either adding push on rings to act as
capacitance hats, electrically lengthening the t match, or swedge on lengths
of rod to extend the t matches.

The design freq of the antenna is very sharp: 49.5 to 50.5MHZ but I can't
seem to stay within 2:1 at 50.315. Running 1 kw is an issue for the amp.

The other, not preferred option is to run a short segment of 70 ohm coax as
a transformer but I will lose output/receive in the form of heat.

We hung the antennas about 10 ft in the air to sweep so the numbers are
fairly accurate.

Any help or suggestions would be appreciated.


Paul Rollinson, KE1LI



860-208-8814 Cell/Text

  <mailto:Paulrollinson@sbcglobal.net> Paulrollinson@sbcglobal.net

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