Thread: 91 XG Modified
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Old 11-Jun-2020, 2:00 PM   #10
tripelo
Senior Member
 
Join Date: Jan 2010
Location: Dallas, TX
Posts: 173
Quote:
Originally Posted by bobsgarage View Post
...49 miles south of Milwaukee, in this case. I aim to Milwaukee since it is farther than Chicago. Plus I have a dense maple opposite! Here's my Rabbit Ears report:
Thanks for the RE report.

Looks like you have several strong signal stations to choose from.


Quote:
...That would probably make sense in my case although consistently 556 MHz the 163 XG is at least 6 dB better than the 91 XG consistently.
As you know, there are several other factors that affect received signal strength besides antenna gain.

Quote:
... I am a little disappointed in my stacking attempts though.

I do have 3 brand new 91 XGs ready for testing and one other I can assemble.

I am tempted to play with a quad array but.... I don't know yet, I am going to perfect my dual stack first.

I want to attempt the twin lead lossless balun though.
The ferrite choke balun is actually a 'less-loss' balun. It can be less loss than the common commercial 300:75 balun.

There is no such thing as a lossless balun* (See Note at bottom).


Quote:
...I think the twin lead endeavor is my best hope for low loss stacking.
There are some interesting challenges with twin-lead stacking.

Quote:
...I will keep you all informed!
Thanks.

Quote:
..Special ordered the ferrite for the loss less balun two different types, one for VHF and one for UHF:
Yes, it is better to try to optimize the type of ferrite for the frequency to be rejected.

Quote:
This is all new to me. Any tips?
No really great tips come to mind:

In general, the more ferrite you use, the less loss.

One of the main goals is:

To impede signal loss down the outside of the coax shield by raising impedance as high as practical on the outside of the coax shield.

For example: If one is using only two ferrite cores, it may be best to use one at the junction and one about a quarter wavelength down the coax. If three cores, maybe two at the junction and one a quarter wavelength away. There are other combinations.

Have implemented the separated cores in test installations. Haven't actually tried to measured improvement results, but have run computer simulations that indicate it is better than putting all the cores at the junction.

--------------------

If you go with a quad stack:

- Need to decide of what configuration you want:

1. Diamond Configuration
2. H Configuration
3. All 4 horizontal
4 All 4 Vertical

As usual, some configurations may be more desirable than others.

Be interesting to see how you handle some of difficulties related to use of twin-lead.

Twin lead is a conductor, depending on location, lengths that are longer than about quarter wavelength can resonate and affect antenna patterns.

.




------------------------
Note, baluns and loss:

Some antennas can be built such that the the transformation of 'balanced to unbalanced' occurs in the antenna. Log periodic antennas can be built in this manner. Some specialized folded dipoles can be configured to make the transformation. As such, these transformations are more efficient than most any other method. There are many other types of antennas that provide for an unbalanced (coax) connection and require no external balun.

Last edited by tripelo; 11-Jun-2020 at 2:32 PM. Reason: Add: Note on Baluns
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