[TowerTalk] Open wire measurments

[Wes]

Okay,

1)  Measuring the impedance of the line isn't a trivial undertaking.  The 
conventional method (with a device such as yours) is to make two reflection 
measurements, one with the line open-circuit and the other with a short-circuit. 
The equations for calculating line parameters are out there, but a better way is 
to use AC6LA's "Zplots" program (https://ac6la.com/zplots1.html)

As has been suggested elsewhere in this thread, you might be tempted to try 
connecting the balanced line to the unbalanced test port of the analyzer, in the 
belief that since it is a "floating" device it's also "balanced".  This has not 
worked for me.  I believe the reason for this is thus:  With an open, short or 
other pair of highly reflective loads, the loads are not only terminations, they 
are balanced sources too. The terminations for these signals propagating in the 
reverse direction is the instrument, which with OSL calibration is 
mathematically "perfect" except, if for no reason other than its physical size, 
isn't perfectly balanced. So the line radiates; it's part transmission line and 
part antenna.

(I was actually trying to quantify this on a 100' length of window line out in 
the yard but when the temperature hit 100 degrees, I decided to wait until 
cooler WX.) For true open wire line, I think you would do just fine using the 
equations, which work well.

2)  I'm not sure you mean measure the antenna impedance at its terminals or 
through the line at a different feedpoint.  If the latter then you don't really 
have to know the line parameters anyway.  You take what you get and match it, 
which is pretty much why you use low-loss lines in the first place.

3)  If you are going to stub match then you don't need to fuss with impedance 
transforming baluns.  Use a good common-choke, appropriate for the frequency and 
stub-match to 50 ohm.

Wes  N7WS



On 9/3/2019 5:17 AM, Neal Sulmeyer wrote:
> First to measure the impedance of the home brew open wire feeder. Then measure the antenna impedance when at its final operating position/height. Finally to use stub matching on the open wire to match to the balun (whatever ration is required) and then coax back to the shack.
>
> On Tue, 09/03/2019 08:05 AM, Wes <wes_n7ws at triconet.org> wrote:
> What parameter(s) are you trying to measure?  Why?
>> Wes  N7WS