[Elecraft] LDG antenna tuner with 132 foot balanced dipole similar to a G5RV antenna

[Bob Stephens]

What is the significance of using RG11 75 ohm coax vs 50 ohm?  Sorry if this is a dumb question.

Bob AF9W


On Oct 26, 2012, at 10:39 AM, N5GE wrote:

> All,
> 
> There's a trick I learned from an antenna engineer acquaintance
> recently for tuning 450 ohm feedline's with a 1:1 balun with 50 ohm
> coax feeding the TX.
> 
> Here it is:
> 
> 1. Assemble three RG11 coax lengths.  One coax 6 feet 7 inches long,
> one coax 6 feet long and one coax 9 feet long.  From these three coax
> lengths you can test with four different lengths of 75 ohm coax; 
> 6' 7", 12' 7", 15' 7" and 21' 7".
> 
> 2. Beginning with the 6' 7" cable and connect the coax between the
> balun and the 50 ohm feed line, repeat the test below with each of
> the lengths above.  Connect the cables with double female connectors.
> 
> 3. If you have an analyzer (MFJ analyzers work fine for this) that
> gives the Rs, Xs and SWR go to step 4; If you don't go to step 6.  If
> you have an AIM 4170 analyzer, you are in luck.  The AIM allows you
> to do single shot analysis of a single frequency, displaying more
> information than you need for this test. 
> 
> 4. Record the Rs, Xs and SWR of each combination at the frequency you
> are interested in.  A spread sheet makes this a little less tedious.
> 
> 5. After recording the calculate the SWR the tuner will see with the
> following rules:
> 
> Disregard Xs.
> 
> If the Rs is greater than 50 divide the Rs by 50.
> if the Rs is less than 50 divide 50 by the Rs.
> 
> The result will be the SWR the tuner is working against when
> searching for a match.  
> 
> In my case I am looking for a calculated SWR lower than 10:1 to help
> my KAT500 tuner find an acceptable match to my KPA500 and NVIS Loop,
> which works on all amateur bands for close in Non-DX rag chew
> communications.
> 
> 
> 6. You can still do the test, but you will need to do it by testing
> with the tuner for the best combination of matches at each frequency
> of interest.
> 
> If you are going to do the tests, remember to use the MINIMUM power
> your tuner can tune with and allow time for your rig to cool down
> between tests.
> 
> 7.  When you have completed your tests measure the length of the
> joined test coaxes, including the double female connectors, and make
> a piece of RG11 that length.
> 
> DISCLAMER:  I'm not a real technical guy and probably don't know as
> much antenna theory as many of you, but what I have described worked
> for me.  Your experience may not be the same.
> 
> Amateur Radio Operator N5GE
> ARRL Lifetime Member
> QCWA Lifetime Member 
> 
> 
> 
> On Fri, 26 Oct 2012 05:42:20 -0700, Ron Midwin
> <ronmidwin.mo at gmail.com> wrote:
> 
>> I recently bought an LDG AT600 Pro Automatic Tuner.
>> 
>> I seem to be able to get a low VSWR on 80 & 40 meters, but on 20, 15, & 10
>> meters the best it will do is ~ 1.8:1.
>> 
>> My "G5RV" (It's really a Van Gordon 80 meter all bander fed with 450 ladder
>> line, 33 feet long, and then transitions to coax thru a 1:1 choke balun;
>> coax is ~ 6 feet long.
>> 
>> Has anyone found a configuration that works better on all the bands?
>> 
>> Previously I have been using an MFJ 962D manual tuner that is able to tune
>> down below 1.2:1 on all bands.
>> 
>> AE6RH
>> K3 S/N 1997
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html