I have been testing with the original ST2 Scantenna.
The testing has been slow at this point, I am using a NANOVNA to test the original ST2
antenna as a means or basis for points of resonance for comparing the Searcher II to the
original design. I have tested many times and I am getting what I call Conflict in the results.
The main issue is the NanoVNA is a 50ohm device designed to measure devices that are
50ohm's. The ST2 as well as the Searcher antennas are both 75ohm antennas.
So this is causing issues with the testing, I have NOT tested the Searcher antenna yet.
I have a good ongoing discussion on RR over this issue, and the overwhelming response is
that I need a 50-75ohm matching pad and a 75ohm load to get the most accurate results with this NanoVNA analyzer. The point has also been made that just using a 75ohm LOAD to calibrate the
analyzer might work as well. Do you calibrate the VNA with the Open/Short/Load AT the VNA or should you attach the Coax to the VNA and place your Open/Short/Load at the end of the Coax?
Should I use a 50ohm coax for testing or a 75 ohm coax for testing?
There are many options and there are as many opinions, If I have to I will try them all and do a comparison to see not what gives the best results but how consistent the numbers are, That is what I want to know, Is it Correct and is it Consistent.
So at this point, I am doing some research as to how to get this testing to the point that
the numbers or results are consistent and as accurate as they can be using the NanoVNA.
I have calibrated the VNA using just a 75ohm load without the matching pad, I will post those
results soon, I am alos planning on buying another NanoVNA and the matching pad(50-75ohm)
and seeing what the difference in results is.
I have to get the ST2 tested properly before any testing on the Searcher can be done.
I will try my best to keep the updates coming.
I have tested again the ST-2. The results although I am sure are not to the standards of a much more expensive piece of equipment is at least showing me numbers that are usable in this persons mind, Your ideas and thoughts may vary, and that is perfectly acceptable.
I have numbers from two different VNA setting.
Setting #1: VNA Calibrated with Open. Short, and a 74.8ohm Termination cap to resemble the 75ohm load. This was all done right on the VNA. I recorded a full scan of SWR and db Loss from 30MHz-1000 MHz.
Setting #2: VNA Calibrated with 75ohm RG-6 (the testing coax) coax attached to the VNA, Open,(before I attached the coax), Short - Shorting cap attached at the end of the coax(antenna end), Load - 74.8ohm Load attached to the end of the coax(antenna end). Again, I recorded a full scan of SWR and db Loss from 30MHz-10000 MHz.
From what I had read, and I have read allot about this, The preferred method would be to use a matching pad, and a 75 ohm load. However, also in my leading, the Average LOSS in using a Matching Pad is 5.2 - 6.2 Loss with 5.7 loss being the standard for most Matching Pads. Also In my Reading it was pointed out several times that the Mismatch between the 75ohm and the 50ohm was only 0.2 Loss.
SO your going to be loosing basically 5.7 db loss when you use a Matching Pad, and you only loose 0.2 loss when you just load with a 75ohm load (74.8 ohm in my case).
SO right or wrong I have two set's of numbers and there is a difference between calibrating the VNA at the VNA and then calibrating with a coax inline, I again was testing what Others have mentioned of how to Calibrate for the testing I want and need to do.
One of the suggestions was that I had to use 50ohm coax, problem is, this is NOT a 50ohm antenna.
I may at some point try a LMR-400 test coax but other testing needs to be carried on first.
Some will say the information about the matching pad loss is NOT TRUE and laugh at the fact I mentioned it and laugh even harder when they found out I actually used this 74.8 ohm load without a matching pad, That's all fine and dandy, I have numbers that may be off BUT I have something to compare the Searcher antenna to and a platform from which making adjustments to the Searcher will reflect in the numbers and that is going to put this antenna at where I WANT IT TO BE.
I will put up so Charts very soon.
I am HOPING to run the first set of test's on the Searcher this weekend.
Keeping in mind, I have been testing the ST-2 for almost a month now, so Testing the Searcher will not be a quick task.
THE TESTING CONTINUES................................................
Today was the first day of looking at the numbers on the Searcher II antenna
I have gathered 4 pages of information from the ST-2 and now I have the
first set of numbers for comparison.
Documenting all these numbers takes a ton of time, on average by the time I get the tripod
setup and the mast pipe leveled then mount the antenna and attach the coax, calibrate the VNA,
and look at all the parameters of the antenna your looking at about 3-4 hours if there is no delays.
Then the numbers need to put into a chart for comparison, just looking at the numbers is hard to tell
what is what, but when put into a flow(type) chart you can very easily see the difference between the
ST-2 and the Searcher, Charting all these numbers again take a Ton of time.
Bare with me, I am working on the first chart or what will probably be many many charts before all is said and done.
The photo to the right is the first look at the Searcher II antenna, the spread is 30-900MHz.
Better photos will be posted in the Photo's section.
I have planned several changes to see what affect they have on the antenna, Some of the simple things like, mounting another section of tubing to the top of the mast to see what affect the mast has on the antenna when both the bottom and the top long radials have mast pipe behind them, Same situation if you were to mount this antenna in the middle of a mast instead of at the top of the mast.
Under what I would call normal mounting the top radial is above the mast pipe in free space and only the bottom radial is affected by the steel mast pipe. It's been said, Mounting an antenna (any antenna) of this type, which there are very few , mounting it to PVC would produce a different affect on the antennas performance since the metal/steel mast pipe reflects off the antenna radials, when using a PVC of other type NON-Metal mast the coax replaces the metal mast and now the coax becomes the affecting character behind the antenna radial, so in a scene, using PVC and running the coax straight down the PVC is the same as using a metal mast, TRUE?, I will find out.
I will add length to the antenna mast to cover both top and bottom radial, then I will mount the antenna to PVC and run the coax down it like normal and see if in fact it has the same affect on the antenna, also while mounting on the PVC I will run the coax 90 degrees to the PVC instead of down the PVC and see what affect that has as well.
Since no one and I mean no one can explain the ST2 antenna as far as it's function capabilities as in how does this thing work? Well I made a copy and by experimenting with the copy I plan on answering all those questions.
I will remove the Parasitic element and see what affect that has on the antenna and what bands are more affected then others. I will remove one set of Wing elements and see what that affects, I will move the wing elements up and down the main radials and see what that does. I will remove both sets of wing elements and see what affect that has, I will them start adding length's of aluminum tubing to ALL the radials and see where that affects the antenna, this will show me what to make SHORTER or LONGER depending on which band I am trying to get the best match on. I also plan on moving the matching transformer to the Center of the antenna instead of being at the front of the antenna, This should produce a BIG difference in how this antenna works. There are other little things going to be tried as well.
So as you can see, by doing all these different test I will be able to pin point certain bands and make this antenna a perfectly balanced antenna, I also have a feeling that other antennas just like this only with certain modifications will be born from all these test, a Dual band 200-400MHz and 800-900MHz band antenna? Sure why not, this type of antenna is more then capable of being a Dual Band antenna. But for now, Let's just see what kind of information we get by doing as many test as we can Dream Up.
I have a base line for testing now, So let the testing continue. STAY TUNED.......................
It is well known that the ST-2 antenna is directional, and just by reading the small Wiki information shown above, This is the only thing you need to know. The fact that it has a Parasitic Element tells you it is a Directional antenna. OK. So what else?????
I tested the Searcher II antenna with the Parasitic Element(Tube) removed from the antenna.
The results were surprising to me, The VNA scans from 25-1000 MHz showed very little affect on the overall response both in SWR as well as DB Return Loss. The only noticeable changes were 450-1000 MHz. but the changes were so small I spent no time logging any data.
I thought by removing this element I would see a big change, I was wrong, appears it's sole purpose is to act as part of the Directional aspect of the antenna and NOTHING MORE.
So i knew the Wings (some may call ear's) had to play a roll in coverage, so I decided to do a little test.
I removed both wings from the lower main radial and from the top main radial, now the antenna has no wing elements and is just all round tubing except for the brackets holding the secondary radials to the main radials.
SO I re-calibrated the VNA, and using my Excel base line number chart, I scanned each band from 25mhz - 1000mhz to see what affect removing the wings had, And yep I found out what those wings do.
Affected bands 100- 400Mhz for the biggest change and some slight changes however small to the 450-480Mhz bands.
I noticed right away looking at the numbers that the 100-400 mhz numbers were much different.
So now I know what affect these wings have I go back to start.
I reattach all the wings Upper and Lower, I recalibrate the VNA and I take all new readings from 100-400Mhz and I chart them for comparison. as I always do, I chart the Peaks and the Dips of the VNA, Those are the numbers I am interested in The Best (dips in the VNA) and the Worst (peaks in the VNA).
I have all my new numbers from re-scanning, I then take the WIngs back off (again both top and bottom) and I DO NOT RE-CALIBRATE the VNA. I now chart all the numbers in a side by side chart on the peaks and dips. Now I have a comparison for just the affected bands of 100-400Mhz. As mentioned there was a Slight change in the 450-480mhz bands but that was a small window and the changes were not that great so I did NOT take any data from those areas.
I have other tests planned surrounding these wing elements, I want to move them up and down the long radial to see what affect that has as well, that will more then likely be one of my next test.
At the time of this posting I have not had time to chart the numbers, I will get to it ASAP when time allows and post that information, but for now take a look at the VNA photo's below and see the affect the wings have when they are removed from the antenna. Numbers will follow shortly.
I think this area needs more testing, this will be a critical area of the antenna to get The Searcher II antenna to a better place for MilAir then the ST-2, as it's directly affecting those bands.
As you can see by the VNA scans and by the Charts, The Wings have very little affect
on this antenna when mounted in the location that was stock with the ST-2 antenna. Will moving the location of the wings have MORE of an affect? We shall see. More Wings Testing Needs to be done.
There was a mention of 450-480MHz showing slight changes, they were so slight they looked identical when I charted them, I will check this range again when I move the wings for the next test.
The original Prototype antenna "The Searcher I" had round tubing for Wings instead of the
flat aluminum plate like the original ST2, I opted to use the round tubing on the prototype because
I really didn't thing the Wings need to be flat plate, So now that I know the wings are affecting the antenna in the 100-400Mhz range which is a desired band width to me personally, I am going to take the round tubing off one of the prototype antennas (i have 3 of them fully assembled) and replace the aluminum plates with the aluminum tubes, who knows maybe I was right to us round tubes on the original prototype antenna, We shall see.