A99/Max2000 Poll and Discussion

[BOOTY MONSTER]

ill start a new thread about omni ground elements effecting a beam below them so we don't hijack this thread .

http://www.worldwidedx.com/cb-antennas/112294-omni-ground-elements-effecting-beam-below-them.html

 

[W5LZ]

Those 'CMC's traveling on the outside of the feed line. In the case of the 'A99' or Imaxx antennas, that outside of the feed line -is- the other half of the antenna, the 'groundplane', or 'counterpoise', or whatever you want to call it. That's for any "no-ground" antenna, not just those two. Get rid of -ALL- the CMC's on the outside of their feed lines and you just stopped that antenna system from working.

That TOA doesn't mean that there;s nothing above or below that particular angle, it only means that that TOA 'lobe' is where the most signal is. There's still plenty 'under' or directly below that antenna, and straight up too. Got a field strength meter? Go see for yourself. One common 'goof' made by almost everyone is the 'scale' of those radiation patterns. The boundaries, the outer edges, are much further than they appear from the antenna's position. I don't think there's a printer or display screen that can make a 'dot' small enough to keep the scale of the antenna's size in relation to the signal's 'spread' even close to 'scale'.
How the feed line leaves the antenna, how it's positioned/shaped, is a factor in using any antenna with no "groundplane"/counterpoise/radials/whatever you want to call it's 'other half'. It can have a very pronounced affect on the 'shape' of that antenna's radiation pattern. Think about it...
- 'Doc

 

[VA3ES]

Those 'CMC's traveling on the outside of the feed line. In the case of the 'A99' or Imaxx antennas, that outside of the feed line -is- the other half of the antenna, the 'groundplane', or 'counterpoise', or whatever you want to call it. That's for any "no-ground" antenna, not just those two. Get rid of -ALL- the CMC's on the outside of their feed lines and you just stopped that antenna system from working.

I'm not so sure. These 1/2 wave antennas like the Antron, are simply 1/2 wave dipoles fed at the end, hence an "end-fed half wave". You can feed a dipole anywhere along it's length; all that changes is the feed-point impedance. When fed at the end the feed-point impedance climbs to somewhere around 600 ohms or so, hence the need for a matching network.

As far as the TOA exhibited by any half-wave antenna, I'm less concerned with the actual TOA, than I am about the actual RF Field emitted by the antenna. I'm saying that these 1/2 wave jobs seem to concentrate the field closer to neighboring houses, as opposed to the horizon. I'm not sure why this is. My 5/8ths wave Penetrator seems to get out farther, and interferes less with neighbors electronics. Hmmm...

 

[W5LZ]

You're right, you can feed a 1/2 wave length antenna anywhere along it's length and the only thing that changes is the input impedance. But, there has to be two 'terminals', a (+) and (-) for current to flow. If the end of that 1/2 wave length radiator is the (+), then where's the (-) terminal? If there's an impedance transformation circuit used then the output of that circuit has to hav both of those terminals to, so where's the (-) terminal? In either case, that (-) terminal is the feed line (in the case of coax being used, it's the -outer- part of the shielding (at a minimum, at least a 1/4 wave length of it). If a choke is placed in side that first 1/4 wave length, then you've effectively "cut off" that part of the 'other half' of that antenna. Not so good, huh? At least that first 1/4 wave length of feed line does radiate, because both 'halves' of all antennas radiate, even those radials making up a 'groundplane'. Since RF is an alternating current, those two terminals swap polarity each 'half' cycle. The (+) then becomes the (-) and the (-) becomes the (+). Exactly the same for that 1/4 wave length of coax 'stub' on the bottom of a 'Ringo-Ranger', below that impedance matching device (the 'circle' thingy).
The radiated RF field of any antenna is very concentrated at the antenna, there are no 'holes' where there's no radiation. Those 'holes' or lesser radiation areas only develop at quite a distance from the antenna. Doesn't make any difference what kind of antenna you're talking about, all of them have that characteristic. That "quite a distance" thingy is frequency related, as in more than just a wave length or two.
- 'Doc

 

[VA3ES]

I'm going to go and revisit the RF current node distribution of the half-wave antenna. That will explain everything.

 

[wavrider]

You're right, you can feed a 1/2 wave length antenna anywhere along it's length and the only thing that changes is the input impedance. But, there has to be two 'terminals', a (+) and (-) for current to flow. If the end of that 1/2 wave length radiator is the (+), then where's the (-) terminal? If there's an impedance transformation circuit used then the output of that circuit has to hav both of those terminals to, so where's the (-) terminal? In either case, that (-) terminal is the feed line (in the case of coax being used, it's the -outer- part of the shielding (at a minimum, at least a 1/4 wave length of it). If a choke is placed in side that first 1/4 wave length, then you've effectively "cut off" that part of the 'other half' of that antenna. Not so good, huh? At least that first 1/4 wave length of feed line does radiate, because both 'halves' of all antennas radiate, even those radials making up a 'groundplane'. Since RF is an alternating current, those two terminals swap polarity each 'half' cycle. The (+) then becomes the (-) and the (-) becomes the (+). Exactly the same for that 1/4 wave length of coax 'stub' on the bottom of a 'Ringo-Ranger', below that impedance matching device (the 'circle' thingy).
The radiated RF field of any antenna is very concentrated at the antenna, there are no 'holes' where there's no radiation. Those 'holes' or lesser radiation areas only develop at quite a distance from the antenna. Doesn't make any difference what kind of antenna you're talking about, all of them have that characteristic. That "quite a distance" thingy is frequency related, as in more than just a wave length or two.
- 'Doc

Doc I agree with all you have posted in this post, I was a firm believer in the splatter stick that am IMAX 2000 would be, after reading pages and pages of reviews at EHAM and ROBB's posts about it I went and spent the money and had one shipped.

I did not tune it, I just assembled it, wrapped an RF choke and placed it at the feed point and then swept it with the analyzer.
10,11,12,15 meters were all useable with decent VSWR and bandwidth, 17 was so so but the FT1000 built in tuner had no problem tuning it.

So with the RF choke at the feed point I eliminatd the 1/4wl of coax from being part of the antenna system per say, in theory anyway.

That fiberglass fishing pole works and works well, for around $100, four bands no tuner required and 5th band with a antenna coupler, not bad price for the antenna. Some say they work 20 meters with it I have never tried.

 

[walterb]

Doc, Booty Monster,
Doc has so eloquently stated what I was trying to get across to another CBer a while back from a practical perspective of what I believe happens on a Big Stick, A99 and I-Max antenna. By moving your feed line coax or changing its length to some degree will effect the direction and angle of radiation of your antenna system. Case in point a station that uses a stick antenna, got out very well in three different directions but did not get out a far near as well in my direction. They moved the radio room from one end of the house to the other an rerooted the coax using the same 100' of coax that has changed the signal strenth at this location. CMC can be seen by using a field strength meter running it up and down the outside of the feed line coax used, the less shielding the coax has the stronger its effects your signal strongth meter an if you cut the coax at a null point an put a connector on it, hook the deiver up then check the SWR at the null your SWR will read very close if not 1 to 1, so no extra heat will be generated because your driver will be seeing 50 ohms. The driver will be able to use full output with out generating extra heat, an that could be a good thing for an..................Oldtimer

 

[BOOTY MONSTER]

so the coax was radiating more signal than the antenna up in the air ?
why not just stick a dummy load on top of the mast rather than the antenna ?
the dummy load should also provide the perfect match for the amp to run cool and send maximum power to it .

BTW ....... what the recommended length of coax for lowest TOA from a antenna ?

 

[walterb]

A99 / I-MAX

BM,
1. Your First question, the coax the antenna is all radiating, by taking a field strength meter it could be plotted if you want to know!
2. Because that's what radio people do, try an make a better mouse trap, every different car or different truck that has a 1/4 wave whip is slightly different in radiating because of where the whip is place and the difference in body styles ther not the same. not much but something is different.
3. Which would you like for your antenna a 1/4 wave whip or a dummy load, if I were trying to talk across the street ether will do just fine, but if you are want to talk across town then I would take a 1/4 whip!
4. Not sure I know what TOA is but I did said to ya on another post that I found that 100' of coax sounded loudest on these three different antennas the HGP-500 the RS Crossbow .64 and the Sigma 4 ground plane antennas because its has a 100' to radiator, like the 1/4 whip works better for distance than the dummy load, I found that by checking many many stations in the club I belonged to in the the 70 & 80s over a 1000 members I checked the loudest station an asked questions found all had 100' of coax in common, 100' of coax also does something else, it gives a lower SWR that
the diver sees over a broader bandwidth because of the loss in the 100' of coax the driver see, so you are using loss to work for you neat! This can be checked with an SWR meter easily, hook the antenna to a 3' jumper then to the SWR analyzer check where a 2 to 1 SWR is above and below residence, then replace the 3' jumper with the 100' of coax an check again, then you will know why I used 100'.
Now you asked why a cable that has less shielding radiates more than one that has more, because signals changes polarity + to - and your field inside the coax the center conductor is also radiating. That was covered on the last post by using a field strenth meter to help you. I hope this has been of value to ya, I have given you the best answer I can, I have read books about radio and theory but in practice I have alway had to change something to make it work correctly, sometimes big some small but change something to get the results I was looking for 73s..............Oldtimer

 

[BOOTY MONSTER]

thanks for the reply walterb

1 . from your comment it seems the coax was radiating more than the antenna in your direction . i realise all coax can radiate , but if its putting out more signal than the antenna above it id suspect something was very wrong with the antenna .

2 . i understand about the vehicle and where the antenna is placed on a vehicle changing its pattern .

3 . id rather have a properly working antenna than a dummy load , but if my coax were putting out more signal than the antenna id want to fix/change the antenna .

4 . TOA is take off angle . you commented "By moving your feed line coax or changing its length to some degree will effect the direction and angle of radiation of your antenna system." i was asking what coax length do you recommend to take maximum advantage of the effect you mentioned . i do understand that raising or lowering a antenna can change its TOA , but till now ive never herd it suggested (before now) that coax length had anything to do with it

i'm not at all buying that 100 ft of coax is louder than another length unless the other length is so long that several db is lost through it . i can't imagine how any length of typical coax on the cb band would sound louder than a similar or shorter length . coax is not a amplifier or a device that produces gain FWIU , its just a way to get the signal from one point to another and can only produce loss . i would love for someone to try to explain how that happens though .

"Now you asked why a cable that has less shielding radiates more than one that has more, ...... "
i don't recall asking that , but i would think that the reason coax with less shielding radiates more is because more signal is escaping from it than coax with more shielding . i dont understand why anyone would want their coax radiating more signal below the antenna that the antenna above the coax . but everyone is free to run their station as they see fit . my goal is to have the antenna doing the transmitting and receiving rather than the coax .

if i find any coax with %0 shielding i'll be sure to let you know so you can upgrade to it .

 

[RickC.]

I have an A-99 on a 30-foot mast, strapped to/hidden in a magnolia tree. The antenna itself is spray painted flat black.

My plan was to use this antenna on 12 and 10 meters, and occasionally on CB. I can do that with a tuner if I want, but I was disappointed that the bandwidth of the antenna was too narrow, no matter how the ring was adjusted.

The results I had with this antenna

http://www.worldwidedx.com/cb-antennas/35651-cheap-easy-ground-plane.html

were much better in that regard.

The A-99 itself isn't touching any limbs, and the VSWR curve in its present location is exactly what is was during testing out in the open, so the proximity to the tree does not seem to be a factor.

I have used it on the low end of 10 meters with 100W with no problems, and it has done a fine job with 4W on CB the few times I've used it there. It's fed with 75' of LMR-400 and there have been no issues with RFI or TVI.



Rick

 

[walterb]

A99 / I-MAX

BM,
Coax and antennas both radiate, a field strength meter will show you how much at any given point or as a hole system. If your wanting to learn about antennas an antenna systems a field strength meter is a great tool to see what is happening in the antenna system. I can't tell you the % its radiating but 0% would be called Open Wire or Ladder Line and I used that back in the day on my dipole antenna as the feed line hooked to an antenna tuner, the only problem with it was RF in your radio shack, but the good thing was not much loss at all. The less shielding a coax has the louder the signal on the other end on tests I did back then. After my father and I got to where we could talk 100 car miles consistently from his base to my mobile on SSB I changed out his base R/S 66% shield coax to Beldon 95% shielded coax thinking there would be more RF signal from the antenna higher up, not so we lost 15 miles down to 85 miles, not until we changed back to the 66% shielded coax did we came backup to 100 miles so my conclusion is that the less shielding the better the ears and transmit. and that is what I call loudness that you could hear. down side is when the coax is between the houses it is very close to phones lines in the walls of the homes and that could become a problem for phones. The longer the coax the more coax that will radiating to a point an the broader a low SWR your driver sees, the driver runs cooler over more frequancys on any high Q antenna. R/S coax back then used a number 10 # stranded center conductor and was only 66% shielded, today the center conductor on RG8 coax is a number 13# which is a smaller size conductor but is 95% shielded..................Oldtimer

 

[walterb]

A99 / I-MAX

RickC
I use 100' of RG213 coax on my A99 which is at 38' to the bottom and can talk on 28300-28500 11 meters 12-15, using a tuner on 17 an 20 meter using the tuner in the ICOM 7600 it works well on 10-11-12 & 15. Using a longer coax will make a stick antenna work to it full potential!............Oldtimer::blush:

 

[RickC.]

Oldtimer,

What does the VSWR curve look like for your A-99?

I attribute the bandwidth of this antenna (which does exactly what it was designed to do, by the way) to the matching circuit. I didn't expect it to be a broad-banded as a ground plane, as it has to match 3K or so to 50 ohms, and isn't starting out near 50 to begin with. The end fed halfwaves I have built used simpler LC circuits for matching as opposed to the tuned transformer the A-99 has, but I can't compare apples-to-apples since they were for lower bands. I may build one for 27 MHz sometime just to see, but right now that would be WAY down on my priority list!

The conditions you are seeing could be caused by the coax length just happening to work out in that case, or it could also be an indication of loss causing the greater bandwidth.

 

[W5LZ]

walterb,
I can understand why you have drawn some of the conclusions you have, but I'm afraid that those conclusions are not completely accurate. For instance.
The higher the 'Q' of an antenna the less usable bandwidth it will have. And, the lower the 'Q' the more usable bandwidth it will have. There's no disputing that, it's been proven too many times.
The only 'job' any feed line has is to carry energy from one source to it's destination as efficiently as possible. That depends on several things, but that's all it (coax) was ever designed to do. One aspect of that is the shielding. It should be shielded enough so that things don't affect that energy it's carrying to any great extent. There will always be some affect from less than 100% shielding, but if it's kept to a minimum, it doesn't amount to anything significant.
The relationship between the center conductor and the shiled, the diameters of both and the distance between them is what determines the impedance of the coaxial cable. If those distances/diameters are proportioned correctly, the cable can be of almost any size (within reason). The insulation between those conductors also plays a part in that, some insulators are more 'reactive' than others. It also plays a huge part in how much power the cable is able to handle without arcing.
All feed lines are subject to 'leakage'. That includes parallel feed lines (ladder line), and is very easy to demonstrate, just get it too close to something. It also applies to 'hard line'.
When the feed line starts to radiate, it isn't just a feed line anymore, it's 'part' of the antenna. That can be used to beneficial affect, but it also destroys the purpose of the feed line. If a feed line is properly matched to the source and load, then the only losses to that feed line is resistive. It just don't get no better than that.
The differences in your example about swapping feed lines for your friend is a classic matter of an improperly matched antenna system. No two sections of coax cable will ever have exactly the same characteristic impedance, that includes sections from the same batch of coax cable. It's called "characteristic" impedance for a reason. It means that the impedance will be at least 'close' to whatever is claimed, but there's no guarantee that it will ever be exactly what it's said to be.
If you take that 100 feet thingy and just extend it a bit, a coax cable long enough doesn't even need anything on the end of it for the transmitter to think it's looking into a 'perfect' load.
The thing to do is dig into the -why- of it to find out how come it seems to work out that way...
- 'Doc