[Top] [All Lists]

[TowerTalk] Force 12 - Magnujm 620/340 dualbander comments

To: <>
Subject: [TowerTalk] Force 12 - Magnujm 620/340 dualbander comments
From: (Frank VanderZande)
Date: Thu, 25 Dec 1997 08:05:47 +0000
Force 12 - Magnum 620/340 dualbander comments.

A few weeks ago I asked for comments about this antenna. Several of 
you asked that I post the responses ......these follow.  Overall, 
found comments to be very  favourable, with only 40M F/B & 
bandwidth to think about.

Thanks for the responses. Seasons greetings to all

       - Frank VE7AV


 I do not have this antenna...but I am quite sure that is the
antenna that my good friend XXXXXX recently put up.  I have only 
talked to him once since then...but he seemed real happy.  He 
replaced a 5 element KLM 20 meter monobander, and a 2 element Cush 
Craft 40 that were stacked on one tower.  I think that tower is 140'. 
 I currently have a Mosely PRO-96 at 100', and although it has 
performed as expected, I really am interested primarily in 40 & 20, 
so I have thought of replacing what I have, and the 620/340 is my 
first choice. But, while the Mosely is still in good shape, I hate to 
go to the trouble...hi.

I have a buddy, XXXXXX, who just put one up a couple 
months ago. Give him a line at: XXXXXXXXX

I was one of two tower men when we put it on top of the tower but have
not used it. I know that he thinks its wonderful on 40


      I've installed several of them and they are quite an antenna.
      You get a lot of performance for one boom and 105 pounds.

     The 20 works quite well and 100 feet is a 'sweet spot' for 20M
     operation. One-hundred feet seems to work better than any other 
single height. 

     The only drawbacks on the 3L 40M are that it is fairly narrow in
bandwidth - it's either a phone or CW antenna but not both and that
you have to tune each element individually to optimize the
performance. You have to be able to reach the reflector and director
to do it properly and it should be 30-40 feet off the ground. You can
suspend it from your tramline and can rent an electric lift for the
weekend to do it properly. Any closer to the ground isn't as good. 

     Go for it.

Plays great.  I've had one for about two years at 70 feet and rarely
have to wait on 20 or 40.  Tuning is a bit tricky on 40 meters,
though.  I'd buy one again.

Hi Frank! Saw your note on the reflector.I'm buying one next year,also
the ef180b,going on top of a 70ft trylon.Rotator is a m2 
OR-2800.  XXXXX,   has one and he blasts in here on 20m. His 
is up 100ft.His f/b is abt 10db on 40m.Book sez 16db.Most people 
order the 100mph version.The f-12's take the heavy wet snow just 
fb,and have been tested up to 124mph on a ridge in cal where winds 


I have been using the 620/340 for 3 years and by and large like it
very much.  Mine is at 85 feet.

Two problems exist with mine...
    1.  My manual claims the 2 - 1 SWR band width on 40 is 300 KHz.
Nonsense.  The real number is 145 KHz.  I have two friends in XXXXX 
who use the same antenna  (XXXXX and XXXXX)  and they also get 145 
KHz.  I have discussed this problem with Tom at Force 12.  He has 
changed the manual to now state 190 KHz but there is no way that can 
be achieved.

    2.  The F/B on 40 is 12 - 14db.  Also much less then advertised.
Again, the other guys here find that is the real number.

Otherwise the antenna plays very well.  I never call more then once or
twice on 40 and I own 20.  The 20 meter F/B and F/S is fantastic.

Tuning the 40 meter elements of the antenna is not difficult, but it
can be tedious and time consuming.  Yes, the elements should be set up
with the antenna in the air.  I used an MFJ analyzer and found the
resident frequency of each element was stable above 30 feet.  Happily
for me, I am using an 89' crank up tower so the job was easier then
doing it on a fixed height tower.

When I adjusted the reflector I shorted out the driven and director
elements.  When I adjusted the director I shorted out the driven and
reflector elements.  I don't know if the shorting out of the "other"
elements was necessary but my thinking was the element I was working
on was "seeing" the other elements and shorting them out would make
them invisable.

After the reflector and director are tuned it's a simple job the set
up the driven element at full height by trial and error since it can
be reached from the tower.

Be sure to move all the jumpers an equal amount on each side, ie., if
you move the left side out 1" also move the right side out 1".

By the way, I have tuned mine for 7.025 and it works greatl there.  I
use a tuner the 2 or 3 times a year I visit the phone portion on the
band and although the pattern on phone is degraded it still O.K.

Let me know if you have any other questions.

P.S.  You too will own 20!!


FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>
  • [TowerTalk] Force 12 - Magnujm 620/340 dualbander comments, Frank VanderZande <=