Marconi comparison testing his A99 without a feed line and mast.

[Marconi]

I posted this video results in an old thread earlier, but I post it again in its own thread, so it will be easier for me to locate using a thread search.

As noted earlier, I did this comparison test using my VA1 analyzer several years ago. I was trying to confirm the idea that the A99 uses the mast of feed line in order to work effectively. In other words this antenna uses the mast and/or the feed line to satisfy the missing radials. My idea was that maybe the antenna would show a corruption to the match if the feed line or mast was not present when testing at the feed point using an analyzer.

Earlier I tested without isolating the antenna from the mast, and some argued that the results I was seeing was in error...because the antenna was simply using the attached mast. So this time I isolated the A99 from the mast to check and see if that would make a difference.

This is my story for how and why I did this video, to indicate finally that I have some proof <gotproof>, that IMO anyone can test and duplicate.

Here is the video:

A99 test with my VA1 analyzer - YouTube

My notes below are the results when checking the battery in my VA1 connected to a dummy load and to the antenna before I did the video test. This routine indicated to me that the meter was working up to par and had enough voltage. As noted the results were very similar, between my dummy load, and the feed point on my A99. If I had seen a notable difference I would have changed the battery.

 

[Marconi]

Here are the results that Northern35 reported a couple of months ago when he tested his A99, at the feed point, with no feed line, using his VNA analyzer, and its blue tooth device connected to his isolated A99.

http://i17.photobucket.com/albums/b90/sambosun/No-coax_zpsd1da2b9c.jpg

If one checks this result out it would be easy to figure the idea to test an A99 at the feed point, with no feed line, and mounting the antenna isolated from the mast...was not a good idea, and the A99 physically requires the feed line and/or the attached mast or else there is a bad match indicated when using an analyzer.

 

[Grinder74]

Have you guy entertained the idea of taking the tuning circuit out of the ant. and testing these same ideas?

 

[Marconi]

Have you guy entertained the idea of taking the tuning circuit out of the ant. and testing these same ideas?

74, some years ago I had an A99 that was very bad acting with TVI. I took the bottom section apart to check if I could see a problem similar to the issues being claimed by many on the Internet...that the solder workmanship at Solarcon was not very good.

You will see in the image below where I found the shield side of the coax at the coil was never tinned, and the small wires were all fanned out looking like a bad hair day.



The image below is from an article showing what is inside the A99 done by Tech 833, on the Copper's Website and Forum.




I repaired the mess of wires with solder, added some wire to the end of the bottom section radiating wire, hung this from an oak tree, and attached the coax. Even with the matching device outside of the metal mount, the TVI was very much improved. I didn't really test anything...all I was really looking for was to maybe find a physical problem and fix it if possible.

After that experience, I was convinced that some A99's, that I owned over time, were bad to the bone, because of this manufacturing oversight. Back then I probably wasn't even aware that there could be an issue with the feed line radiating...but I knew what TVI did in my shack and the neighborhood.

 

[Grinder74]

Have you thought of a better way of setting it up, without the guts?

 

[Marconi]

Have you thought of a better way of setting it up, without the guts?

What do you have in mind?

 

[Grinder74]

I really don't know. I was just given an old A99 but always heard about tvi problems. I use a 102" with 2 opposing 102's for radials. I would like a better omni and wondered if it was worth the switch but I live in town and don't want to cause interference.

 

[M0GVZ]

Have you guy entertained the idea of taking the tuning circuit out of the ant. and testing these same ideas?

It won't work. Because its a halfwave or longer it is voltage fed, not current fed, and therefore requires a matching network in order to present a 50 Ohm impedance to the transmitter.

 

[W5LZ]

An 'A99' is an end-fed half wave antenna. That means the input impedance is quite high (+/- about 1000 ohms). The 'guts' in the bottom of an 'A99' is for impedance matching or changing to 50 ohms for the feed line and transmitter. If you remove that matching device then you either supply another method of doing that matching or end up with a really 'large' SWR.
There are a number of ways to do that impedance matching, the way the 'A99' does it is just one of them. That particular method may not be the 'best' in the world, but it does work and is fairly cheap/simple. Wanna try a different method? Have at it!
- 'Doc

 

[Lil'Yeshua]

I'm thinking that the A99 needs to be grounded only as to provide a more direct path for lightning to follow instead going the the radio shack.