SWR ON A IMAX 2000

[cominatyalive]

Thanks Doc,

That was on my mind as well. Gramps had stated that before as well. So the bottom line, if your antenna is not resonate with the frequency your on, or with the Bandwidth your using, it ain't worth squat, no matter if you've got a good SWR reading or not. Gotcha.

And that goes hand in hand, for if your antenna is resonate, the SWR should be good to go as well? or could it still be off? but one shouldn't have trouble in getting it to specs if it's a good resonance. Makes sense to me.

Impedance has to be matched as well. I'm thinking an antenna tuner might be in order here.

Say Doc, therefore would it be wise to invest in a antenna matcher? Is a antenna tuner different? I think I saw some that were both, am I correct? Is it wise to have both if I plan on venturing to 10 meters in the near future?

We check SWR by using a meter, how do we know if our antenna is resonating nicely? Geez, I've really got to go back a bit and re-read whatever I can about this. I know you guys get tired of answering the same o'l questions over & over again. But the good thing is, that I am taking in quite a bit of this antenna jive.

Oh, btw, Merry Christmas to you and your Family!
And thank you for your wisdom.

I also just wanted to apologize to Stephen and the rest of you guys.
Last night wasn't a very good night for me. I've been exhausted lately.
I didn't mean to jump all over him. Don't know what came over me.

I hope everyone has a great day tomorrow.
I'm going to just kick back now and try to absorbe all the things you, Gramps & rob have said, and even think about what Stephen is going through with his antenna.

Night all & see ya around in a few days. Time to rest, read & pull my head out of my rear for once. The fresh air might do me good eh?



later

 

[WA2FDU]

Merry Christmas all.............................

Antenna's are a mix of Science, Theory, SWAG, and Black Magic.

To cover the first 2 areas in depth, I would highly recommend the following book.

The ARRL Antenna Book
ARRLWeb: ARRL Product Catalog

Answers to the many questions can most likely be found there.

Mine is the 1968 11th Edition that cost $2.50. I guess it would be nice to upgrade to the 21st Edition and get some of the tools on the CD.

Please remember that a 'Antenna Tuner' does NOT tune the antenna. It is designed to protect your rig and amp, and to make them think they see a proper antenna out there. That's how apartment dwellers can toss out a 20' piece of wire and work 80 meters. The overall performance is lousy - but usable. And the rig could care less because it thinks it sees a 80 meter antenna. Personally, I use a Palstar AT2K for HF that feeds into a Carolina Windom 160 Special.

True antenna tuning is changing the physical characteristics. Thus, I want to tune my imax 2000 by changing it physically for absolute peak performance in the 10 meter band.

Wishing all of you a Very Merry Christmas and a Happy Cycle 24.

Stephen

PS - Cominatyalive, we're cool!!

 

[Robb]

An antenna tuner won't make your antenna more resonant. But it will change the impedance so the radio will see 50 ohms. That will keep the finals from frying. Tuners are used by Hams mostly, often because they run a multiple band dipole or a multi-band antenna - like a G5RV. Which will cover frequencies between 10 meters all the way up to 160 meters (28.4mhz to 1.6mhz respectively). When they use an antenna tuner on some of these frequencies, they often do so at a loss of power and without efficient resonance. Antennas that try to do too many bands are often said to be a compromise of antenna resonance and efficiency. Antennas that are single band designs tend to do so with great efficiency.

With an antenna like the IMAX, it has a broad band transmit capability centered on the 11 meters/CB band and is said to be relatively efficient. When signal strength is tested during transmit on different frequencies within the antennas design - measured with a field strength meter/antenna analyzer - it will be found to be more efficient on a center frequency and diminishes/falls off as you move away from that frequency on either side of that center frequency. The IMAX is said to be most resonant -stock- at/around 27.500mhz. That doesn't mean that it is crappy below and above that frequency and is unusable; it just means that it is most effective at that point. Because the IMAX is a broadband design - it will easily work 1.5mhz above and below its most resonant frequency. So don't throw your antenna away or get an antenna tuner - you don't need to for a single bandwidth use. Unless you want to run that antenna on 12-15-17 and 20 meters with an antenna tuner. In which case, the tuner will allow the radio to transmit on those frequencies w/o burning out the finals with a 3:1 SWR match - because the tuner will make up the difference in the SWR.

Will it work well on those suggested frequencies? Yes and no. Yes; because the radio will throw some power to the antenna. But not efficiently - because the tuner will end up absorbing the unusable power because the antenna won't be resonant to do it itself. No; because there isn't as much power to use as you would expect. Receive will also have compromises. I'm not saying that it won't work; it just won't be able to work as efficiently as an antenna that is being used that is a tuned length for that frequency.
At least, that is my understanding at this point...sorta kinda...

 

[W5LZ]

Rob KI6USW,
That's about as close as you can get without some math, paper work, that nasty theory stuff, which just explains why something works the way it does. I figure that's pretty well got it nailed, kind'a, sort'a.

Just a little bit more will explain why that 'efficiency' of an antenna, or how 'well' it will work, might be helpful. So here's a couple of definitions.
Reactance.
Reactance is a way of measuring how something "reacts" to an alternating current flowing through it. It comes in two 'flavors', inductive reactance (+), and capacitive reactance (-). Inductive reactance means an antenna reacts like it was longer (+) than it ought to be. Capacitive reactances means an antenna acts like it's shorter (-) than it ought to be. Why longer (+) and shorter (-)? Because the length of the antenna is about as 'simple' a way of determining resonance as you can get, how it was done in the first place. That's not the only way of making something resonant but it is one way. So what's the deal with reactances, why do they count for anything? The biggy with reactances and antennas is that reactances do not result in any radiation, reactances do not contribute to making power (only resistance does). So, if there's any reactances present that are not 'neutralized' by an equal amount of the opposite kind of reactance ((+) + (-) = '0'), then something isn't going to be radiated from that antenna. That antenna isn't resonant, and isn't radiating as efficiently as it could be radiating. So something ain't going out, and that means it's going somewhere else, which is not good. That's pretty 'black and white', right? Hang onto that thought, cuz it gets sort of 'gray'.
If everything was 'perfect' you'd always have a resonant antenna. But, since nothing is ever 'perfect', there's a lot of 'gray' areas that are almost as good as 'perfect', and that are certainly usable without much loss in efficiency. Oh crap, one'a them things! Yep, get used to it, there's a bunch of them. So, until the losses from that loss of efficiency from those reactances get to be more than you want to put up with, 'close' to resonant can work pretty good. How do you determine if it's more than you want to put up with? Measure it some way, then it's just up to you. One way of doing that measuring is by using a field strength meter. That's certainly NOT a very accurate way of doing things though! But it can get you into the ball-park, so to speak. Finding your seat is more than it can do for you. You are trying to measure how much power is getting radiated by that antenna, so figuring how much is going in and comparing it to how much is coming out is the idea. Another 'side' of that is that if it ain't coming out, it's gotta be going somewhere else, right? So, if everything else in the antenna system is very close to 'right', measuring any reflected power is also a way of determining efficiency. (Did the light bulb over your head come on? As in SWR meter? But there's a 'catch'!) The 'key' in that is that everything has to be 'right'. Meaning matching impedances between transmitter, feed line and antenna. Which brings up that nasty 'impedance' thingy, which is composed of (R) resistance and (X) reactances. It seems that reactances in feed lines isn't a very nice thing to have either. Yeah, well, I told you there was a bunch of that 'gray' stuff, that's just another example.
Reactances are NOT always a bad thing to have around, if they are in the right places! They do a pretty good job if transforming impedances to the 'size' you want, if you put them together right. That's why tuners work, and even the right lengths of feed lines (-although- since feed lines were never meant to do that 'transforming', they have definite limits, they aren't the 'best' way of doing that).
That's about as far as I'm going with that. It's more than you wanted to start with so since I have to deal with two inches of that white stuff, and since I haven't had near enough coffee to do that yet, I'm going to quit here. I figure if I get enough coffee, use a little imagination, I can go outside and cuss that @#$ white stuff and it'll melt! Scares the dogs, but they'll get over it...
- 'Doc

 

[cominatyalive]

Merry Christmas!

Morning all,

Well the white stuff is melting here today Doc, lol!
I woke at 9:00am to about 40 degree F weather. And I fell asleep at my computer last night between Capacitance & Reactance. The light bulb is on, but I'd be kidding myself to say I had it all in the bag.

I appreciate all of the info you guys are spittin out at me. And it does jive to what I've been reading. I typed "Antenna Resonance" into google and it's all there.

Stephen, what you said makes sense. I can see now that it all depends on what one is trying to accomplish. What bandwidth & frequencies one intends on using the most, then adjust one's antenna accordingly to get the best performance on a particular frequency, or within a range of frequencies.

Oh I'm not tossing out my Imax yet Rob, I agree with you on not having to have a tuner for 11 meters, but how about 10 meters? That's where my next step will be by springtime most likely. Kinda the same direction Stephen is taking. Reading the info Stephen has been posting, I can see that I'm still far behind in that field. And I'm ok with that. I'm just glad that there are guys out here that I can relate to, and be able to understand what they are going through & the steps they are taking also.

Doc,
Yes, a lot of gray here, but I'm beginning to absorb something here everyday now. I do have a field strength meter on that Workman SWR/Watt meter I purchased for $20.00 last week, new off of ebay. That's when I started questioning the accuracy of my PAL KW-1 SWR/Watt meter. Because the PAL reads 10 Watts on dead key, the Workman only 4 or 5 Watts.

That's why I just wanted to make sure the SWR on both meters were giving me the same readings first before I went any further trying to find the cause of the different wattage readings. Also, I noticed when Trying to place the needle on (SET) on FWD with the PAL, it is very hard to get my needle on the PAL to stay put on (SET). It's so very sensitive it seems as compared when setting the Workman meter's needle on (Set).

The Workman's needle stays put without any movements. However, the SWR readings on both meters are giving me the same readings. So Doc, as I posted before to Gramps that I was able to get a 1.2:1 SWR ratio on channels 10 & up after I moved the tuning rings farther up the threads, is this really improving my overall performance? As I was getting 1.4:1 or higher with the factory setting about halway on the threads. If I go any lower than halfway, the SWR only gets higher, 1.4 to 1.6:1 even.

From the info you gave on capacitance & Reactance, I am assuming this is being adjusted when I move these tuning rings, correct? Making my radio think the antenna is longer or shorter. And since I'm getting a better SWR, should I just leave the rings at this higher level on the tuning ring threads and start looking into the impedance matching, the field strength with the meter, and resonancy now? Or should I worry about the SWR last?

I did remember you said that the SWR meter could still give better readings and the other things could still be off. Or should I just keep on trying to improve all the things mentioned and take it from there? I always was a believer in always going forward and never go backwards in reverse sort to speak.

This is why I need the dummy load, so I can make sure my meters are calibrated correctly first before I start assuming. And you know what they say about (Assuming) dont ya?

I've read that when using a field strength meter, that one should go up to their antenna and plot out (Chart) the field of the TX. However, their were no instructions that were clear about how to use the meter in this. I am guessing you just hold the meter and walk around? I have the little field strength antenna hooked up to my meter and I get no signals in my shack upon transmitting. So I would guess that is a good thing? ( meaning no stray RF is coming back to my radio?).

Other than that, I have no other issues I suppose.

Rob, yes,
As I go back & forth from the low end of the band to the higher end, the SWR is always best on the high end from Channels 20 & up. 1.2:1 on channel 40 and 1.4:1 on channel 1.

However, today the readings are different, 1.5:1 on channel 1 & 1.3:1 on channel 40. Is this normal for the SWR to change from day to day? I heard it was, but just thought I'd throw it out there at ya.

Channel 20 is about 1.3 & a half to 1.
Right now, it's not worth it to go up on the roof today, but when the weather is better, I will retune to channel 20 again. I will also take notice of my readings from day to day. Seems like the better the weather, the better my SWR.

As Gramps said before, the antenna comes pre-tuned from Solarcon at 27.205Mhz, (Channel 20) as a halfway point in the band. They state that in the manual. However, that frequency is not really the true halfway point. 27.185Mhz is. 27.405 - 26.965 = .44Mhz Half of that is .22 + 26.965 = 27.185 Mhz

When punching in this frequency of 27.185 into a antenna length calculator for a 5/8th wave, the calculator says my antenna length should be 21' 6 1/4" but the IMAX comes stock from the factory at a whopping 24'

How can this be? or does the Imax come 24' to accomodate the 10 meter band? Beats me. Mmmm.

Here's the software calculator URL for verticals.

Amateur Vertical Antenna Calculator by dxzone.com

That leads me to wonder, isn't that a lot to adjust even with an antenna tuner? 3 feet worth. Is it worth it? This also leads me to believe that one should cut their antenna to the right resonance if one wants the very best performance on a particular bandwidth or desired frequency. One thought does come to mind though, 10 meters is 28.000 to 29.700Mhz.

And the length of antenna according to the calculator does decrease as you go to a higher bandwidth. This might be due to Solarcon already figuring this out?

But when you punch in the halfway frequency of the 10 meter band which is ( 28.850 ) 29.700 - 28.000Mhz = 1.7Mhz / 2 = .85Mhz + 28.000Mhz = 28.850Mhz

The length of the antenna should be even shorter ( 20' 3 11/32" ) according to DX zone's calculator for verticals.

With the IMAX coming 24' from the factory mind you.

My Mind is a clickin'!

 

[bob85]

just a couple of points worth thinking about in a hotly debated topic,
i like walt maxwells version of whats happening with mismatched loads tuners and wave interference,

power reflected from a mismatched antenna does have to go somewhere but when using a tuner at the line input to achieve a conjugate match, transmitter power is not lost or absorbed by the tuner,
power reflected from a mismatched load is rereflected from the tuner or transmitters tank circuit back towards the load and eventually radiated,
the losses are mainly feedline loss in both directions, if the line is short and the tuner well made ( not a lazymans autotuner ) the transmitter will deliver full output to the system and virtually all of that output will be radiated even with a mismatched antenna,

while the tuner cannot bring the antenna to resonance it should bring the system to resonance.

 

[mackmobile43]

just a couple of points worth thinking about in a hotly debated topic,
i like walt maxwells version of whats happening with mismatched loads tuners and wave interference,

power reflected from a mismatched antenna does have to go somewhere but when using a tuner at the line input to achieve a conjugate match, transmitter power is not lost or absorbed by the tuner,
power reflected from a mismatched load is rereflected from the tuner or transmitters tank circuit back towards the load and eventually radiated,
the losses are mainly feedline loss in both directions, if the line is short and the tuner well made ( not a lazymans autotuner ) the transmitter will deliver full output to the system and virtually all of that output will be radiated even with a mismatched antenna,

while the tuner cannot bring the antenna to resonance it should bring the system to resonance.

I could not of said it better bob.

 

[WA2FDU]

D I T T O ! ! ! !

 

[Robb]

cominatyalive;

The IMAX will be just fine on 10 meters as is - w/o a tuner. Mine is. The IMAX's matching coil and natural capacitance makes up for some of the difference. I use the IMAX on 10 meters all of the time w/o any difficulties or using a tuner either. Talks quite well over a large distance w/o any help when DX is in - I might add. It is when you try to make an antenna work on a frequency that it wasn't designed to do - that a tuner has any real credible use. Like if you were trying to make it tune up on 20 meters - for an example - which is waaay out of its resonant point. So the tuner will need to make it electrically longer than it is. But not mechanically/physically longer as it requires to be resonant on that band.
Go with it - dude!
I think you made a fine choice.

The IMAX is a .64 wavelength antenna; which is BETTER than a 5/8 wave.
That is why it is 24 ft - instead of 22 ft.
In fact, I've considered lengthening it by 1 ft 9 inches to see how it would behave as a 3/4 wave antenna - for $#!+s and giggles.

I have read how some guys have taken an old bed's box spring - and wired it up to an antenna tuner. This is just used as an extreme example to make the point that an inefficient radiator can be used if the tuner can make it reactance work at 50 ohms. Some guys have used the rain gutters around the circumference of their house - that amounts to a horizontal 'loop' antenna using a tuner - and made it work quite well. Due to the fact that the circumference was physically almost the correct length for that frequency. You can make anything an antenna with a tuner; doesn't mean it will work well at all. It just means that it will match the impedance so the radio won't fry out.

But tuners can also be used to make up for the subtle mismatches on multi-band dipoles - for which they have their true use.

Bob85, I don't really know where the power loss goes. Maybe to Cleavland - or Ipswitch? (just kiddin!) But seriously tho, it cannot work on an antenna that isn't quite resonant - I agree. So it must have loss everywhere in between the radio and the radiator. I know that the mfrs of antenna tuners boast of having high power usage before the tuner itself begins to arc. That must say something about the point of the system that finally breaks the transmission chain when an arc becomes evidence. At least, that is how I look at it to this point. Sorta/kinda...

 

[cominatyalive]

Thank you to all.

Never mind about the antenna lengths, Stephen explained why the length is greater than what it's calculated out to be in the antenna length calculator software on DXzone.com.

Thanks Rob, I am feeling better about my Imax now. Thanks to you, Doc, Stephen, Gramps, Bob and the rest of ya who are shedding some very important information here.

I didn't realize what a can of worms I opened up here. It's amazing how a SWR meter post can turn full blown into Resonance, capacitance, reactance, tuners and such. I've taken in much just in the last two days.

I have a few new ideas, and a newer understanding than I did days ago.
I'm looking forward in heading into 10 meters and at least now, I have a direction and a goal. Plus, better knowledge & understanding of antennas, SWR, and resonance.

I think I'll just sit back now & focus on that Dummy load I'm trying to build. I'm going to use a quart paint can, and two round fiber boards instead of brass ones. I may use the 300 Ohm 5 Watt resistors, or order 20 1K ohm 3 watt ones, but they run about $6.50 a piece. I'll just make due with what I've got for now.

TY to all for all of your help. Especially since it's on the Holiday.

I cannot thank all of you enough.

OK, gotta go, my finger is hurting from typing now!


Merry x-mas
Over & out!

James

 

[W5LZ]

[I can't resist!]
Same old thing, 5/8 w, or 0.64 w, don't know whether to laugh or cry. A difference of about 6 inches, and people are making so much 'to-do' about it. That other 18 inches of difference, where is it, and what's it consist of? Wouldn't be that impedance matching device's length, plus maybe the part that clamps onto the mast, would it? I don't think either would be part of the antenna's vertical radiating length, they typically aren't counted in the 'radiating' part making up an antenna.
As far as that 'additional' length's radiating ability goes, model the thing, see for yourself! No practical difference at all. Best marketing ploy I've seen in quite a while.
- 'Doc

 

[cominatyalive]

Now here's some reading for ya! (chuckling),

You got a point Doc, and I agree.

What I had a hard time with is, when using DX Zone's vertical antenna calculator software for a 5/8th wave antenna, and tuned to the freq of 27.205, (the same freq Solarcon tunes their antenna's to), why the length was coming out at 21' 6" when the Imax is actually 24'. we're talking 2' of difference or so here.

Stephen & I came to the conclusion that it was due to the coil not being considered when using the software calculator.

Anyways, that may hold true or it may not, but something is not quite kosher there.

So I'm just going to accept our hypothesis on that for now. Anyways, I called the electric company & told them about that pole out back & the woman said they would look at it. When that will be I haven't a clue.

On a brighter note, for the last two days, I have not had any AC inteference from the neighbor woman's underground electrical drop from that telephone pole to her house. Nothing but 1 to 2 s-units of pure, loving, ground floor noise finally.

I don't know if it is from the ground being covered with snow & insulating the interference or if the electric company did anything yet, (and I know they haven't), or if the woman turned off her stupid bug zapper that she always keeps on in her garage, even in the dead of winter mind you.

And before I go to bed, I'm going to my window that allows me to look into her garage without going outside & see if it's finally off or not. Maybe that was causing the hum. If not, it's still at the pole but not acting up right now.

Whatever the reasons, I really don't care, all I know it has been really wonderful listening on my Magnum 257 for the last two days & I hope it continues to be that way.

My SWR is holding around 1.3:1 or so from channels 20 & up. So I can't complain.

Oh yeah, just thought I'd mention this, and it's just a coincidence, that just two days ago, I took the 20' ground cable for my radio off of my mast's ground rod. I can't be for sure yet if that was acting like an antenna, but it just seems kinda funny that my crackling AC hum is totally gone now. (For two days also mind you).

Mmmmm. just keeping my head clear here so that I know what's going on with every little change or move I make that's all.

Heck, if the noise stays gone for weeks, it would have to be something that has changed, right? Anyways, I should never of had the radio equipment ground cable that long to begin with, but I had no choice as there is some kind of cement pipe all along the side of the house, about a foot & a half down in the ground, all the way from my shack's window, to the Mast's ground rod. Nice antenna eh?

Fortunately for me, the only place I can put a 8' ground rod is near the house's neautral service ground rod. Only there is it totally clear of this cement pipe or foundation that is underground all around my house. It just may be part of the cement foundation for all I know. Remember now, my house is 106 years old.

So when I get a chance, I'm going to pound a single ground rod that's only 2 1/2' long, diagnally into the ground, (already done it) outside my shack window, only 3' from my radio on the other side of the wall, & we'll see how it goes. I haven't reconnected a ground cable yet to my equipment, but the shorter rod is in place. Later, I may remove it and put a longer one in, at a greater angle so I can at least get about 6' of it in the ground or so.

AS per my conversation with Sam from Magnum last week, he said to unhook my Mast's ground cable off of my Neautral service ground rod & put a seperate ground rod in the ground, just for my mast, nothing else. So I have done that also, but the noise was still there. It wasn't untill I removed that long ground cable for my radio & equipment from the mast's ground rod that the noise finally vanished. Like I said, I'll see how it goes from day to day.

Right now, everything is hunky dory. (keeping my fingers crossed)
Over & out.

James

 

[wavrider]

[I can't resist!]
Same old thing, 5/8 w, or 0.64 w, don't know whether to laugh or cry. A difference of about 6 inches, and people are making so much 'to-do' about it. That other 18 inches of difference, where is it, and what's it consist of? Wouldn't be that impedance matching device's length, plus maybe the part that clamps onto the mast, would it? I don't think either would be part of the antenna's vertical radiating length, they typically aren't counted in the 'radiating' part making up an antenna.
As far as that 'additional' length's radiating ability goes, model the thing, see for yourself! No practical difference at all. Best marketing ploy I've seen in quite a while.
- 'Doc

Doc you hit it on the nail head. " marketing".

I have built the 5/8 wl gp, have built the .64 wl gp. Both with ground plane radials. No noticeable difference in tx or rx.

Marketing at it's best.

Happy New Years to all

WAV

 

[Robb]

A 5/8 wave, .64 wave, 3/4 wave, and a 7/8 progressivly have lower angles or radiation.
Apples and oranges?

 

[W5LZ]

Rob,
The 'change over' point for that lower radiation angle is somewhere close to the 5/8 - 0.64 wave length region. The lengths longer than that all have higher radiation angles, not lower ones. The particular length of that 'change over' point isn't definite, it's variable because of the antenna's environment and mounting height, etc, but it's right at/around that 5/8 wave length. You'll also find that the take off angle, or radiation angle is cyclic depending on length of the antenna. As it gets longer angles lessen to a 'low' point then start to rise again. Somewhere at some frequency related 'multiple' of a 'basic' length, that large angle starts down again. It cycles like that till some really ridiculous lengths are involved, where that cyclic change starts flattening out. (Don't bother asking me, I have no answers/numbers for that.) The -practical- length is reached long before that 'flattening out' range is reached on HF. Phasing one of those 'shorter' lengths, using a vertically phased array, is more practical in general than just using one long solid length. Play with the numbers for that sort of thingy and you'll see that real quick.
- 'Doc

[If you've got the physical ability to do that sort of testing, rather than a theoretical testing with modeling programs, etc... would you adopt me??]