SWR ON A IMAX 2000

[cominatyalive]

As some of you know, I have a IMAX 2000. I have a couple posts about this antenna. One on AC crackling hum, (some may call it static), I call it received interference. In dealing with this Stray AC interference over the last couple months, led me to start getting a grip on my SWR.

They all say that the IMAX 2000's SWR is a good 1.4:1 on the meter right out of the box. Well, that might be so. At least mine was at first that is.

I use a PAL KW-1 SWR/Watt meter. But it was telling me that I was putting out 10 Watts on TX. Which led me to believe this meter was out of whack. Especially when I went to put the needle on (SET) right before getting my SWR reading. It was always 1.4:1. But it also always reads 10 Watts on TX.

I just now purchased a Workman SWR/Watt meter. Low & behold my SWR on channel 20 was a solid 1.5:1 and my TX wattage was about 5 Watts like it should be. But 1.5:1 is just way too much for my liking.

So up I went to the tuning rings on my IMAX. As I lowered the rings all the way down, (let's say from the 1/2 mark of the tuning threads and down to the bottom, I got nothing but a 1.6:1.

From the half way level of the tuning threads and all the way up, nothing but a solid 1.4:1 and no better.

What I wanted to know, is there anyone out here who has a better reading than a 1.4:1 on their Imax's? I'm just wondering if a Imax is even capable of a better SWR reading than the 1.4:1 from the factory.

Back in 1976 or 77 when I had the original Avanti Astroplane, I had nothing but a solid 1.1:1 always. Those were the good o'l days. I'm thinking it may be from a not so perfect solder job on my PL-259's. Not that I don't trust my own work, but sometimes I wonder.

Also, I wanted to know if there are other ways of improving one's SWR? Is it possible to raise or lower the antenna height to improve on this? I sometimes also wonder if my antenna is too high. 60' to the tip. Penny for your thoughts.

J.

 

[Robb]

I have a 1.2 match on my IMAX. They are adjustable; they have two rings on the lower portion of the antenna that has threads. Moving the rings up and down will raise/lower the SWR to where you want it. it might be a pain in the posterior to get it right; but once it is set right you will be good to go...

But first - consider this:
One of your meters is right - and the other wrong.
Or - they are both wrong...

To test them both out and adjust them internally, you need to make/get a 50 ohm dummy load (check the resistance on the dummy load with a digital meter first - to be sure that it is 50 ohms). That should give you a 1.1 match when testing each SWR meter. That is how to know if one is right and the other wrong - or both are wrong...

 

[fodendaf]

I run about 170 feet of 75 ohm thicknet coax to an A99 and I was mystified as to how to get the swr below 1.6. I realised the handiest way was to put the swr meter at the bottom of the antenna and tape the mike button down at a low power of 2 watts or so so I didn't get an rf burn and screw the rings and keep an eye on the meter.

 

[cominatyalive]

RE: Dummy Load & taping the mic down,

Rob,

I read somewhere about the 50 ohm test and I thought I had sent the url's to my email address so I could go read about it when I got home.

Needless to say, I couldn't find the info I thought I sent to myself.

So thanks for the important info Rob. BTW, is a dummy load something I have to buy? lol! I haven't a clue so I will search the net in the time being. When I have a dummy load, can I adjust or calibrate the wrong meter?

Fodendof,
Good idea about taping down the Microphone TX button. But I have old, well known, sure fire method that goes back to the stone age, (My Wife). lol!
I purposely use a set of motorola hand helds so I can just scream at her to key the mic, set the set line in FWD, then take the reading of RFD. Yes, I have her trained.

I also have her walk around the house pulling light switches, unplugging devices & the sort. Now if I can only get her to climb the ladder! ;-)

Well, anyways, so far I haven't went back up to the roof yet since the other night when I adjusted those tuning rings. Currently, I'm getting 1.2:1 or so on channels 30-40 and a 1.3 to 1.5:1 on channels 1 through 29 or so. Not bad. But my Workman meter shows a different TX wattage than my PAL KW-1 meter.

I'll try the dummy load test as soon as I learn a bit more.

Thanks guys.


J.

 

[Robb]

50 ohm dummy loads are most often used by Hams in fine tuning their radio first, before they transmit. In this way, they can send the output power into the load rather than their antenna. The reason being, that it is improper practice to transmit interference due to an improperly tuned output (power, modulation, width, etc). Things that CBers don't need to concern themselves with.

Radio techs also use them for fine tuning the radio at their shops. Or if one just wants to check out a radio that one has bought; then all you would need to do is a)power up the radio b)then use a jumper cable and hook it up to a power/modulation meter c) and put the dummy load on the output of the meter - instead of an antenna. That is what I do when I mess with any internal modulation/power adjustments on a radio I'm working on. Does that help?

From another thread http://www.worldwidedx.com/cb-band-cb-radios/17904-galaxy-pluto.html:
One of the 'best' ways to calibrate the SWR meter in that Galaxy Pluto, is to build your own 2:1 SWR dummy load. You will also need to look up the proper VR pot for the internal SWR fine adjustment for that radio. Maybe you will have more luck finding it out better that I did. Or maybe someone on this forum knows where to find it?

You will need an old/usable PL-239 male plug, and four - 400 ohm/2 watt resistors. Solder them in parallel across the PL-239 from its center to its shield. Check it it with an ohm meter and be sure that it reads 100 ohms across this plug from center to shield. Since a 50 ohm equals dummy load will give a 1:1 SWR on the meter; then a 100 ohms will equal a 2:1 SWR on the meter. This will make it easy to calibrate the SWR meter on any internal SWR meter in any radio.

But if you don't feel comfortable with messing with the adjustments in your radio to make it right; then off to the shop it goes...

 

[cominatyalive]

RE: Pluto & internal swr meters

Thanks Rob,

While I was waiting for your response, I looked up a bit of info as well.
But where did you get Pluto from? I have a Magnum 257 blue LCD. If I'm not mistaken, it's Identical to your Magnum S45, correct?

As a matter of fact, mine just returned from Magnum. But not for SWR problems, it's brand new. Maybe you were just using the Galaxy Pluto as a reference?

I'm having SWR problems with one of my external, standalone SWR meters, or both of them. I know one of them is giving me a false Wattage reading. AS I speak though, they are both giving me identical SWR readings, but I just wanted to make sure the readings were correct. So I asked about the SWR of the IMAX 2000 antenna. And you say you are getting 1.2:1 eh? Well, that's a real good reading in anyone's shack!

I am getting 1.2 to 1.3:1 from channels 30 or so and on up to 40.
From channel 1 to 29 it's 1.3 to 1.5:1 on the single digit channels. I may not get it better than that, but I'm trying.



I have a External (PAL KW-1) SWR/Watt meter. It's the only one PAL makes as far as I know. The SWR reading on it seems to be ok, but the Wattage reading seems a bit high if I dead key the microphone. 10 Watts it says.

So I bought a cheapy Workman SWR/Watt/Field strength meter with the external antenna for $20.00 new off of ebay. It read 4 Watts dead key.
Although both meters give me about the same readings for the SWR, The PAL gives me higher wattage readings than the Workman meter.

I am interested in making the home brew 100 ohm dummy load you speak of. No pun intended Rob, but us CBr's are becoming a bit more comfortable in gaining all the knowledge we can. At least I know I do.

I suppose there are many CBr's who don't give a hoot about the fine tuning stuff, but some of us do. Not to make a mountain out of a mole hill here, but I believe it's just a very good thing to know these things whether or not your a prestigious Ham, or just a so called, (lowly Cb'r). A name that has branded us just because we are just a (Cb'r).

As a matter of fact, I'm not just a regular Joe here, but I label myself one because there are many things I do not know. I know you meant nothing from it, But I do have an Associates in Applied Science in the HVACR field and I am well versed in electricty, ohms, schematics, etc. I have to, as I run the entire refrigeration for a major sausage plant here where I live.

So, since this has become my hobby, I like to venture outside the norm & go the extra mile in this. I know that you know I am a bit of an explorer since I went to Timbuktu & back over the interference coming over my Imax.

I think it's everyone's business to know all they can if they are behind any kind of Radio that transmits.

I will build this Dummy load you speak of. I have the schematics for my 257 here in my hands and I know where the VR pot is for the SWR. If I need to adjust I will, but as I mentioned, the Magnum technician just had it in his hands the other day in Delaware. But that doesn't mean this (Highly prestigious, Magnum Technician) went out on a limb for me & checked the SWR of the radio. But I wouldn't place money on that.

Hope there is no offense taken here. You know more than I will ever probably know. I'm just beginning to explore 10 meters. I have to start somewhere. And that somewhere is at the bottom. I love all this technical stuff. And I eat it up every day.

I value you and others who share what they know. BTW, what about the salt water, home brew dummy loads? lol! ok, ok, I can see you shaking your head right now. Just thought I'd ask you your opinion on using one. Have you ever made one? or is it the easy way out of doing it correctly? I think it's a poor man's device. But I thought it was interesting and just ask anyways.

James

 

[Robb]

Yes, the Galaxy Pluto was used as an example. It was just easier to copy and paste that post so that I didn't have to rewrite the same thing.

I didn't have to adjust my IMAX when I got it.
It had that 1.2 SWR right out of the box.

Some dummy loads that Ham use - are paint cans filled with mineral oil/stacked resistors that are rated for more than a 1,000 watts for the purpose that I mentioned earlier.

I don't think the Mag 257 is the same as the OmegaForce; they don't have the same features to begin with. The 257 was one of my choices before I bought the OmegaForce.

The 100 ohm dummy load is a way of checking each of your meters to know that they are reading correctly. If they both show a 2:1 SWR that is...

I'm a lowly CBer as well as a lowly Ham.
Don't mean nuthin...

 

[cominatyalive]

Just looked at the S45, your right it is different. However there are a few of the same features such as the power/channel selector microphone, split frequency offset, ANL NB, adjustable power, clarifier, and the basics, etc. But yours does have a lot more. Real nice Radio Rob & sorry, my mistake.

So let me get this right, use the 100 ohm dummy load setup to get a 2.1:1 reading because a 2.1:1 reading is easier to read on the scale of internal meters on a broad range of different radios, and most importantly, thus making it easier to just calibrate a radio or a meter, right?

Then the radio can be calibrated. So how about an external meter? so I connect the dummy load to the output of my external PAL meter's S2039 connector correct? As my PAL does have a increment adjustment screw for the needle. But make sure the radio is calibrated first. Am I on the right track? Will this adjustment also correct my wattage reading? If I recall, checking the wattage is a totally different procedure. Or do I have to just accept what the wattage reads? Have you ever heard of the wattage reading in a external SWR/WATT meter being off?

If not, you gotta admit I'm persistant lowly cb'r :tongue:

 

[Robb]

Just looked at the S45, your right it is different. However there are a few of the same features such as the power/channel selector microphone, split frequency offset, ANL NB, adjustable power, clarifier, and the basics, etc. But yours does have a lot more. Real nice Radio Rob & sorry, my mistake.
The 257 is a pretty nice radio. Prone to noise tho - BTW

So let me get this right, use the 100 ohm dummy load setup to get a 2.1:1 reading because a 2.1:1 reading is easier to read on the scale of internal meters on a broad range of different radios, and most importantly, thus making it easier to just calibrate a radio or a meter, right?
Pretty much - yeah

Then the radio can be calibrated. So how about an external meter? so I connect the dummy load to the output of my external PAL meter's S2039 connector correct? As my PAL does have a increment adjustment screw for the needle. But make sure the radio is calibrated first. Am I on the right track? Will this adjustment also correct my wattage reading? If I recall, checking the wattage is a totally different procedure. Or do I have to just accept what the wattage reads? Have you ever heard of the wattage reading in a external SWR/WATT meter being off?
I don't know it the 257 has a built-in SWR meter - does it? Better to adjust yout external meters anyway. The 100 ohm dummy load can be used to setup any radios with built-in SWR meters too - yes

If not, you gotta admit I'm persistant lowly cb'r :tongue:
Hey; this is forum. Where would any forum be without any questions or statements to be challenged?

That's it...

 

[cominatyalive]

Thank you Rob,

No, the 257 is meterless except for the s-rf. Better leave it alone I suppose, but I will test my externals. Thank you for all the info. Time to do a little hands on.

 

[cominatyalive]

RE: Wattage

Rob,

Does it matter if I build a 50 watt dummy load instead if a radio only puts out 4 watts? Wouldn't it be better to build a dummy load that could handle the extra power if you needed to? or does the wattage of your radio have to match the wattage of your dummy load exactly?

I'm thinking of building one using Qty-5, 500 Ohm resistors, 10 watts each. Giving me a 100 Ohm dummy load rated at 50 watts handling capability.

This will also give me the 2.1:1 SWR calibration.

500 Ohm / Qty 5 = 100 Ohms
500 Ohms / 10 Watts = 50 Watts
2.1:1 reading

I am thinking of going with the 500 Ohm resistors because after several hours of scouring the internet for 4, 400 Ohm resistors, (which I found was really hard to find), I decided to change the values a bit to the more readily available 500 Ohm resistors.

What do you think?

 

[Robb]

You don't want to use wire-wound resistors; they will act like inductors.
Carbon resistors are the way to go. Most 50 ohm dummy loads for CB's are used w/o much modulating. So they make them for around ~5 watts or so. You can build them for more power handling capacity - sure. The 5 watt rated dummy loads work OK for short periods of time; not to be used indefinitely.

 

[cominatyalive]

Gotcha, But I'm intrigued a bit here.

Do you mean to say that Hams actually modulate while tuning their SWR?

I'm bewildered, but then again, Having your SWR tuned to the top of your modulation peak would that be even better? Mmm. Better performance at top end sort of speak? lol I don't know!

???

 

[Robb]

Gotcha, But I'm intrigued a bit here.

Do you mean to say that Hams actually modulate while tuning their SWR?
SWR is done last with an antenna tuner - most often. First they will check modulation/power with a meter and an O-scope for an acceptable wave form.

I'm bewildered, but then again, Having your SWR tuned to the top of your modulation peak would that be even better?
SWR last. Tuning modulation/power and freq width first. Typical Ham practice; best Ham practice.
Mmm. Better performance at top end sort of speak? lol I don't know!

???

There it is...

 

[W5LZ]

A dummy load isn't used just to check SWR, although it can be used that way. The only sort of good reason for having a 100 ohm dummy load is because you have something that requires that sort of impedance. (It's AC, so it is impedance rather than just resistance. Impedance is composed of both resistance and reactance.) And when you stop and think about it, how often would you possibly need a 100 ohm dummy load?

Why would you want a dummy load capable of handling more power than you'd ever put into it? So you don't burn the stupid thing up, naturally, which can do more harm than just to the dummy load.

Why would anyone want to 'modulate' while checking SWR? Beats me, it certainly doesn't do any good. But then, if you want to check 'modulation without putting a signal on the air, you'd need a dummy load, right? Why should you not put a signal on the air when doing that sort of thing? So you don't embarrass yourself by the funny noises you make, or what you might say it that 'modulation' wasn't right?
- 'Doc