Question regarding antenna bandwidth for coax vs: open wire line

[K1JJ]

Good info, tnx Norm!

If I build it, now I know it can be precisely tuned, so would buy a NanoVNA.


Do you think by adding each element it will affect the phase placement farther down the line?  I realize that 5' off the ground is close for the elements, even at 10M, so wonder if these phase placements will get corrupted once the array is raised high and put in position.

Yes, bare copper wire will be a better choice. I still have a lot of this THHS #10 insulated from the delta loop openwire tests.

What is your opinion of this array as far as performance and usefulness as a fixed NE/SW bi-directional antenna with near horizon reach?  There is no way to switch to higher angles.   I actually have fifteen 10M elements ready to modify from an old 10M stack of the last solar cycle, so WTF.  The open wire is cheap. I plan to find the 75 ohm tap on the OWL / balun at ground level for the 75 ohm hardline run to the shack.  The only cost would be some bare copper wire for OWL.  The only drawback would be the lack of uni-directional pattern, thus more noise on RX.

T

[K9MB]

I was just seeing if there is a cheap and dirty way to feed three yagis and here is on possibility:

You can make the feedpoints to be 50 ohms and then run a 3/4 wave phasing coaxial cable made of rg11 from the top to the middle of the array. 3/4 wavelength for this rg11 with a VF of 84% is about 41 feet. This may be close to what you need to get to the middle.
Then you do the exact same thing from the bottom yagi to the middle.
Then you put a 3/4 wavelength of rg11 from the middle yagi feedpoint to the node where all three are connected together. It will all be coiled up.
Each line will have been transformed to 100 ohms and when connected together, it will look like 33 ohms. Now, add a 1/4 wave coaxial Q section of rg11 to the feedpoint and then connect a flat 50 ohm feedline from there to the shack.
If I am not mistaken, all antennas will be fed in phase and impedance matching should be close to a flat line as long as the phasing lines are exactly the same length.

It will take 41+41+41+13.5 = 136.5 ft of rg11 and the 50 ohm feedline needed. The loss would be low even with all the phasing-transformer lines.
I may be missing something, but it seems possible.
Phase errors, of course cause grating lobes in any multi yagi array and fine tuning lengths could clean up a lobe pattern if it gets ugly, but f-b is not hurt if elements are tuned properly. 50 ohm common mode chokes can be placed right at the feedpoint. Just a thought….MB

[W1ITT]

Tom...
I can't think of any reason why adding successive elements would cause a phase drift as long as they are pretty much identical anyway.  Going back to my time building FM arrays, I think the longest bottom-fed array I built was 6 elements and we just put them on equally spaced.  In some instances I took phase and magnitude measurements at each bay and never saw any phase drift to amount to anything.
A Venetian array of the size that you are contemplating should have a few minor lobes in the elevation pattern to fill in missing angles.  If not, a separate low antenna, for high angle stuff, could be made cheap enough although it would not have the gain of the stacked monster..
I can't emphasize enough how capable the NanoVNA series of instruments are for the money.  I've made my living for decades staring at the high priced HP and R&S instruments, and own a few.  For amateur use, these Nanos are comparable to the best Alien Technology that ever came off the flying saucer.  Here's an Eham discussion snippet on the NanoVNA Lite series that seems to be the latest.  As to where to buy, I'm not sure... It's pretty fluid.
73 de Norm W1ITT

[W1ITT]

https://www.eham.net/community/smf/index.php/topic,136813.msg1269435.html#msg1269435

Forgot to do the Paste part of cut-and-paste.
N

[W3SLK]

I second Norm's suggestion. The Nano is the bees knees! Once you are finished tuning your antenna array, you will find that they are great for tuning filters and anything else RF related. Make sure you get one with the calibration board. That way you can set and save a calibration for the freq.(s) you are using. I also invested in some small cables with SO-239 connectors on. They usually use SMA's to connect to the Nano so the extra cables make it a little more unwieldy.

[K9MB]

VNAs are impressive. Good calibration modules important and cabling to get best results, I understand. These cheap ones might not be great at 1gHz and speed snd data points limited, but for Hf, they are amazing for the price.

Edit: Sorry SLK, I seem to have posted at the same time as you. 73, Mike

Edit: For a more professional unit for about $600, this SDRKits unit has great specs and far less expensive than a $20K Lab model…

https://www.sdr-kits.net/

[K1JJ]

FB on all!

It's time to start a new thread since the 75M delta loops are finished and we are moving into the 20M 2x2x2 stack and 10M 12 el dipole stack.  I will be having some questions about these projects and the NanoVNA.

Here is the new thread:

http://amfone.net/Amforum/index.php?topic=47651.0

Thanks to all for a very informative, helpful and effective thread!



T