Unscientific antenna "tests"

[unit_399]

I hear so many claims that one antenna outperforms another, but there is never any real scientific proof to back up this up. When I talked to Marconi on 38lsb a few weeks ago, he had three antennas up, and switched from one to another throughout our QSO. I could not see any difference between the antennas on my S meter, but for some reason or another, the audio from each antenna sounded different . Why ??? I don't know. But on that day, his Marconi 7X had the best sounding audio. I've tried to figure out why this happened, but I don't have a clue. I feel that a 5/8 wave antenna is a 5/8 wave antenna, and that the only difference is the manufacturer and the cost. Yet I heard a difference between each of Eddie's antennas, and this has me mystified. I'm about 2500 miles from Marconi, so this is a true DX situation. What the hell is going on here??? Any Ideas that make some real sense would be appreciated.

- 399

 

[MrSuburban]

I hear so many claims that one antenna outperforms another, but there is never any real scientific proof to back up this up. When I talked to Marconi on 38lsb a few weeks ago, he had three antennas up, and switched from one to another throughout our QSO. I could not see any difference between the antennas on my S meter, but for some reason or another, the audio from each antenna sounded different . Why ??? I don't know. But on that day, his Marconi 7X had the best sounding audio. I've tried to figure out why this happened, but I don't have a clue. I feel that a 5/8 wave antenna is a 5/8 wave antenna, and that the only difference is the manufacturer and the cost. Yet I heard a difference between each of Eddie's antennas, and this has me mystified. I'm about 2500 miles from Marconi, so this is a true DX situation. What the hell is going on here??? Any Ideas that make some real sense would be appreciated.

- 399

Possibly Phase differences?

 

[loosecannon]

399, im going to make a guess and say it might be the antenna switch.

anyone who has opened up the typical CB style antenna switch has noticed that they leave a lot to be desired in solid RF engineering practice.

there may be one position that is better than the others.

this is yet another variable that if not accounted for, would make all the antenna test data useless.
LC

 

[Marconi]

399, I don't know why you noticed the difference in audio either, but I've had such reports before, and in fact I think it was my Marconi then too. I also firmly believe the reason such a response is so hard to believe for some is...you have to have two or more antennas up on a switch box in order to switch fast enough to see the difference, and that kind of setup is not too common.

BTW, I checked back on my notes and my videos for that weekend and I didn't have my Marconi 7x up at the time, I had just taken it down and removed the three horizontal radials leaving only the 4 slanted down radials, making it a Marconi 4x. At the time I was intending to add those 3 radials back in the slanted down position, but I couldn't get them to screw into the hub. That said however, I could have called it the M7x when on the air with you, because the M7x had been up for several weeks prior. At the time the other two antennas were my Gain Master, and my 1/2 wave Wolf .50_11m without and ground plane radials.

Mr.S is probably right, the issue you raised was likely a phasing issue in some way. For me that is the big deal that makes DX signals work and sometimes work like a direct line, and it often has nothing to do with the particular antenna or the power used.

LC's suggestions has to be considered too, but I've checked my Avanti Switch box for RF leakage and isolation issues while TX'ing into a dummy load, and it is typically just as clean as my Alpha DELTA-4 switch box. I've never noticed any noticable signal differences either, although I have not checked port to port. I know what LC is talking about though, because I have a Dosy (not a Dosey) test center TC-4002-SW with an antenna switch and they're junk IMO, and leak very badly. Even the connectors on the back are cheap lightweight and use very thin tin sheet metal for the contacts, just junk.

I also looked to see if I videoed that contact 399, but no luck.

 

[unit_399]

399, I don't know why you noticed the difference in audio either, but I've had such reports before, and in fact I think it was my Marconi then too. I also firmly believe the reason such a response is so hard to believe for some is...you have to have two or more antennas up on a switch box in order to switch fast enough to see the difference, and that kind of setup is not too common.

Eddie -

This difference in audio thing has had me really perplexed ever since we talked. I checked my log book, and I had written down marc7x, wolfe,gainmaster. I feel that Mr Suburban is on the right track with his phasing explanation. I've always visualized the rf eminating from an antenna as a huge "cloud" of rf energy whose size was dependent on the wattage inputted into the antenna. With a high power rig this cloud could extend out dozens of miles. The shape of this "cloud" is initially established by the type of antenna being used (vert, horz, omni,directional,ect) but also by things it passes through and around (buildings, bridges, electrical substations) and things passing through it (cars,trucks,planes).So the shape is constantly changing. Personally, I think that the electromagnetic fields around high-voltage power lines play a part too. All of these things can cause the phase shifts Mr Suburban refers to. The list of possible variables is, unfortunately, endless. Or... it may be as simple as the antennas' location with respect to each other. Who the hell knows ???

-399

 

[MrSuburban]

399, im going to make a guess and say it might be the antenna switch.anyone who has opened up the typical CB style antenna switch has noticed that they leave a lot to be desired in solid RF engineering practice.

there may be one position that is better than the others.

this is yet another variable that if not accounted for, would make all the antenna test data useless.
LC

399, I don't know why you noticed the difference in audio either, but I've had such reports before, and in fact I think it was my Marconi then too. I also firmly believe the reason such a response is so hard to believe for some is...you have to have two or more antennas up on a switch box in order to switch fast enough to see the difference, and that kind of setup is not too common.

LC's suggestions has to be considered too, but I've checked my Avanti Switch box for RF leakage and isolation issues while TX'ing into a dummy load, and it is typically just as clean as my Alpha DELTA-4 switch box. I've never noticed any noticable signal differences either, although I have not checked port to port. I know what LC is talking about though, because I have a Dosy (not a Dosey) test center TC-4002-SW with an antenna switch and they're junk IMO, and leak very badly. Even the connectors on the back are cheap lightweight and use very thin tin sheet metal for the contacts, just junk.

I also looked to see if I videoed that contact 399, but no luck.

Just a qucik note regarding coax switches. I had a alpha delta 4 position switch, I was getting intermitent contact one day, so I opened it up and once I saw how it was made . I fixed what was wrong put the cover on it and listed it on ebay all within a 30 minute time span. I sent Bob85 a few pictures and may have posted them on here. It is built like a piece of shit, after opening it up and seeing inside i would never use a Alpha delta switch again, (even though I used it for years) I would never trust my equipment to be used with it. It is easy enough to make your own with a dpdt 20amp relay, 12 volts and a switch and 3 so-239's.

As far as a Dosy they are junk I wouldnt even have one inline, if you gave me a brand new test center i would sell it to the first CBer I saw.

 

[Marconi]

I tend to agree MrS, and that is why I don't use either, the AD4 or the Dosy.

The AD4 does provide ground to all open ports and the contact mechanisms are adjustable, but the manufacture taped the tensioning insulator inside and they should have secured it mechanically, or at the very least epoxied it in place. I figure I must of bumped the switch or dropped it, and the tensioner slipped out of position, and then the reed switch mechanism was out of alignment. It works fine when its lined up right. In fact using my dummy load and my Autek VA1, going direct in and out of each switch, I see the AD4 being a bit closer to the dummy load default on my Autek VA1 for R, X, SWR, Z, but the problem could as easily be the connectors used also. Neither switch seems to be excessively leak with RF, but I don't know if my testing is affected by their use or not since I typically get similar results on both when I've checked and compared signals in the past.

 

[Marconi]

399, in case you missed this SWR bandwidth demonstration video I did using my Marconi 7x, which is made up of 7 x 102" ss whips.

This is not intended to be proof, but maybe it will help give us some clues as to how real symmetry in antenna design can have a positive affect on how they might work. I do BW curves on all of my antennas, and I seldom ever see a better representation of a perfect bandwidth as with my Marconi x.

http://www.youtube.com/watch?v=-JaA8L_HF94


Here is the bases of the Marconi, but the M7x has another hub with 4 ports for whips slanted down right below the one show. This model will make a Marconi 6x.