[UK-CONTEST] CG-3000 vs MFJ-974HB on 160, 80, 40m band

[Peter Hobbs]

Hi Samir

Glad to see your comprehensive approach to antenna design!  It's going to be 
hard to predict the relative performance of your options exactly, because of 
the differences in directivity and knowledge about your ground conditions, 
however I would suggest that you take the following into account from my own 
experience with wire antennas over the past 50 years.

1.    Your options 2 and 3 will perform like a dipole when operating on 
their natural frequency.  At the higher bands you will get some gain 
broadside to the antenna, which may be as high as 3dB depending upon the 
type of ground you have, with a corresponding reduction in response off the 
ends of the wire.

2.    Bringing 450 ohm feeder into the shack (as opposed to coax) may 
possibly cause some RF problems, especially with option 4, because the 
feeder will not be completely balanced.

3.    Rather than making  your wires to the exact dimensions, you may like 
to make them a little longer or shorter (by 5 to 10%).  This will reduce the 
feedline impedance and voltage when each wire is working as 1/2 wave and 
improve the efficiency of the tuner.  The small difference when the antenna 
is working as a true dipole is unimportant.

My personal preference would be either option 1 (with the CG-3000 located 
some distance from the shack and using low loss coax feeder) or option 3 (if 
you can orient the dipole to favour your desired direction(s) and don't mind 
some loss off the ends)

Good luck & 73
Peter G3LET


----- Original Message ----- 
From: "Samir Popaja, 7S7V (SM7VZX)" <7s7v at adamomail.se>
To: <uk-contest at contesting.com>
Sent: Wednesday, November 12, 2008 7:48 AM
Subject: [UK-CONTEST] CG-3000 vs MFJ-974HB on 160, 80, 40m band


> CG-3000; http://www.arraysolutions.com/Products/cg_3000.htm
>
> MFJ-974HB; http://www.mfjenterprises.com/Product.php?productid=MFJ-974HB
>
> Hello,
>
> I need to solve my problem on low bands; 160, 80 and 40m with one antenna.
>
> These are my possible solutions (which is better according to you antenna/
> tuner knowledgeable people).
>
> The antenna will be used primary for contest.
>
> 1. Inverted L (15m + 25m) with radials, feeding with coaxial cable and
> CG-3000 in feedpoint
>
> 2. Dipole (2 x 20m), via 450 ohm open line and MFJ-974HB, on 160m the
> antenna will be used like T vertical and ground (@20m)
>
> 3. Dipole (2 x 40m), via 450 ohm open line and MFJ-974HB (@20m)
>
> 4. Inverted L (15m + 25m) with radials, via 450 ohm open line and 
> MFJ-974HB
>
>
> *What's the behave of solution 2. and 3. against halfwave dipole feed via
> 50ohm coax on 40 respective 80m with same height, @20m?
>
>
> Thank You for all answers/ suggestions.
>
> SM7VZX
>
> _______________________________________________
> UK-Contest mailing list
> UK-Contest at contesting.com
> http://lists.contesting.com/mailman/listinfo/uk-contest
>


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