[Ares-races] Re DXCC at EOC

[Jerry]

Joe,

I have never used the antenna you have, but I am a little familiar with 
the design.  I asked a former co-worker that used one to tell you of his 
experience.  I also read some reviews on eham.net.  In those reviews, 
many people said they had to re-tune the antenna for some bands.  One 
cited trimming 18 inches off the 80 meter wire to move it from the CW 
end to the phone end.  

In the installation instructions, Alpha Delta recommends the use of an 
antenna tuner, especially on 80M.  Two excerpts from their instructions.    

http://www.alphadeltacom.com/dxcc_ii.htm

We recommend the use of a good, wide range antenna tuner (matchbox) for 
use with the DX-CC on the 80M band.

he DX-CC may be operated on the entire amateur HF bands with the 
incorporation of a good antenna tuner into the system!

Generally, any coax fed antenna will have limited bandwidth.  It is 
nearly impossible to take an antenna that is resonant at one frequency 
and make it exhibit resonance at another frequency, USING COAX.  In my 
experience, I have only used one coax fed antenna that exhibits 
resonance in all five amateur HF bands (80-40-20-15-10), and that 
antenna is the W9INN.

http://www.eham.net/reviews/detail/322

Here are the 2:1 SWR bandwidth that I measured on my W9INN MPD5 87-foot 
model, up about 50 feet.  Note that this is a coax fed antenna, and 
these are 2:1 SWR limits, not 1.5.
80M 50 kHz
40M 150 kHz
20M 350 kHz (entire band)
15M 200 kHz
10M 600 kHz

You asked, where do you go from here?  The answer is tuning your 
existing antenna for where you plan to use it, and running a tuner to 
make your transmitter happy when you use it at other, non-resonant, 
frequencies.  You normally start with the highest band and work down.

10M - 1.3 looks pretty good to me - it is on it's own wire, so I would 
not touch it.
15M - ? it is the third harmonic of 40 meter wire - you should plan to 
work 40 far more than 15
20M - 1.3 looks pretty good to me - it is on it's own wire, so I would 
not touch it.
40M - looks to me like it is resonant in the CW end, far from 7285 and 
7290 where you will be operating in Texas ARES nets
80M - looks to me like it is resonant in the CW end, far from 3873 and 
3935 where you will be operating in Texas ARES nets

As already said, the same wire is used for 80 and 40/15 meters.  You 
trim one wire, and it WILL affect the other three bands.  No way to get 
around this.  Start trimming the 40/15M wire section, inboard of the 
coil.  I would start with taking six inches, re-assemble everything, and 
test it again, on both 40M and 80M bands.  You should see both of them 
moving the low SWR point higher in frequency.  Repeat this process until 
you get a low SWR on 40M around 7.150.  Then check it at 7.285 or 7.290 
to see if it is below 1.5:1 there.  If you trim it for 1:1 at 7.285, 
then you won't have much bandwidth at the low end of 40M for HF Pactor 
operation.  If you tell me you don't care about HF Pactor right now, you 
probably will in the future, so you may as well have an antenna that can 
easily go there, as well as the SSB nets at the upper end of 40M.

Once you get 40M taken care of, then do the same thing on 80M.  By 
tuning the 40/15M section for a higher frequency, you should have also 
raised the resonant frequency of 80M from 3.6 closer to 3.873, where you 
need to be.  If it is not quite there, trim a little off the 80M wire 
that is OUTBOARD of the coil at the end of the 40/15M wire section.  You 
should try to get a low SWR around 3.900, which may allow you to work 
both 3.873 and 3.935 without a tuner, maybe.  You won't know for sure 
until you try it.  If you trim too much off, and the resonant frequency 
is well above 3.935, you can always add a little wire to the end of the 
80M wire section.  That does not even have to be directly in-line with 
it, just solder a short pigtail onto the end of the 80M wire and let it 
hang down.

Tuning the 80 and 40/15 meter sections should not have any effect on the 
20 and 10 wire sections, since they are separate wires.

I hope this helps, and let me know the final results.

Jerry Reimer, KK5CA
Assistant Section Emergency Coordinator
ARRL South Texas Section

 


kd5czm1@iwon.com wrote:

>We have an 80-10m DXCC in sloper configuration with the low end up about 70 feet off the ground above the courthouse.  We cleaned up the corrosion, tightened all connections and put an antenna analyzer to it.  
>
>We got the following values:
>
>MHz
>3.59MHz SWR 1.2
>3.75MHz SWR 7.3 very high
>3.873MHz SWR 11.1 
>7.05MHz SWR 1.3
>7.15MHz SWR 1.8
>14.175 MHz SWR 1.3
>28.390 MHz SWR 1.3
>28.500 MHz SWR 1.1
>
>Everything physically, mechanically, checks out. The Alpha Delta hardware is solid.  We think it may have to do with the coils for the 80m legs of the dipole, though they look ok.  Where do we go from here? Your help appreciated.
>
>Joe Guerra KD5CZM ARES EC Kleberg County TX
>