SWR ON A IMAX 2000

[Robb]

The 100 ohm dummy load was being discussed as a means to an end. To use it for seeing that an SWR meter will show a 2:1 SWR; so as to check its acuracy is all.

You must remember Doc; that you are talking to a couple of dummy loads!
:laugh::laugh::laugh:

 

[cominatyalive]

I see,

And before you say to yourself (OH MY GOD! HERE WE GO AGAIN!)
(Joke), believe me when I say "I'll take your word on it".

However, (and with all due respect to you), I have always heard that SWR should always be checked first. Is this just for CBr's?

Not meaning I am not believing in you, but I have heard that an extremely high antenna SWR can & will blow your finals if one is not careful. And blow them right away from the power being redirected back down the feed line if one's SWR is way too high.

I have seen this advice published over & over on the internet from reputable sources. Is there not Finals in Ham radios? Are Ham Radios much different than CB's other than the frequencies & power, and combined computer collaborations?

What I think you are telling me is that it is assumed that an antenna's SWR is kosher before a Ham operator checks his power & modulation? Or it doesn't matter at all about the SWR being checked first & that's just what a Ham operator/tech does last regardless? Sorry, don't mean to be anal here at all.
Just trying to make sense of what you said & what I read about all the time.

And also with very high due respect Rob, I am trying to figure it out for myself without having to ask & ask & ask. I know you guys have private lives like anyone else, I'm just trying to make a little sense out of what you stated.

As I always tell everyone here, I do not know a lot of things. I am not quick to disbelieve anymore like I used to do in my younger years.

I'll be the first to tell you that I know very little when it comes to Ham radios.
H_ll, anyone here can see that. Pardon my french.

I don't argue with the pros. But I do raise a few questions to them once in a while. And I know it just pisses them off! LOL! I can hear the majority now. And I do go to the other ham posts on here as well, so I know it does go on in there. You know, Newbie initiation & the sort. :bdh:

I questioned a top HVACR freezer contractor last week & he was quick to give me a second look before I quickly told him ok. But later I talked to my boss and turned out he was actually wrong. Not saying your wrong at all, but just giving an example on why I ask, and why I sometime's ask seemingly twice.

And Rob, really man, you do not have to respond back right away johnny on the spot if your busy. I have very little time myself. I put in a good 71.75 hours this week at work & this is the first I've been home in the evening time in two weeks, so please forgive my bombardment of questions. If I have asked twice about something, I apologize.

It's hard to relay one's true meanings sometimes through messages & emails, etc. And people sometimes get the wrong meanings or get the wrong impressions. Believe me, I mean no harm and I mean well. Thank you for your patience most of all. I suppose I'll lighten up a bit here, and hey! you get back to me when you feel like it. And I don't mean that the wrong way either.

Hey! I'm a character & that's for sure! I'll run ya ragged before I let go of ya too. But isn't that better than to just sit here and get nothing out of being here other than just taking up some space?

I give you all the credit in the world for putting up with me.

Ya know, it just doesn't matter what subject I am on when it comes to Amateur radio, When I explore into what seems to be a very easy subject, it's almost always the opposite. There is no subject here, no matter how seemingly easy to understand, ever that simple when taken a bit further.

Your a good friend Rob. And I thank you very sincerely for that.

Well, I'm just sitting here listening to the locals on 10. Animal circus you could call it. Disgraceful! just disgraceful!

You know us CBr's, always hanging off your coat tails.

lol! Night Rob.



Sincerely
James

 

[cominatyalive]

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

Thanks Doc,

Makes sense to me. Oh, btw, I need the dummy load to re-calibrate my SWR meters. Not to check my SWR. As a matter of fact, I would never use a dummy load to check my actual SWR on my antenna. And your right, I don't want to build a cheap burnable dummy load. I want one that will never burn up. Seems to me modulation would be something that was dealt with last, but I'm not arguing here. I'm just a little guy.

 

[cominatyalive]

Yeah Rob,

With the economy the way it is, I oughta provide a dummy for hire service.
Sure fire method to raise cash

 

[Robb]

Meant nuthin by it; just joking!
I'm a new Ham and a times still fell like a dummy. Didn't mean to include you on the joke. My mistake!

 

[cominatyalive]

Rob,

No problem at all. I've got to be the biggest joke on here!
I come on strong sometimes & I worry more about aggravating someone, than being the root of a joke. he he,

I'm most guilty of over expressing my opinions & thoughts. Sometimes it gets me in a heap of trouble.

But hey, it's all good. I love it here. Wouldn't leave here for the world either.

Well, I'm trying to hunt down a few carbon resistors & the rest of the pieces I will need for this project.

BTW, what do I mount all this stuff to? A block of wood? op:

 

[cominatyalive]

Still having a hard time tracking down those Carbon resistors. I have an idea for a 1/4 inch thick aluminum heat sink from scrap at work. This thing is going to be awesome, all I need is to just track down a place that sells the right resistors. 400 Ohm ones prefferably, but the combination could change due to what is readidly available. Wish me luck


J

 

[W5LZ]

Just for what it's worth.

I think you'll find that commonly available carbon resistors are going to be sort of small in the watts department. If you can find 5 watt carbon resistors, I think that's about as large as you'll typically find. Larger ones are certainly made, they're just not that common (that's only going by what I can find locally, which is sort of 'sparse' anyway).
There are quite a few combinations of series and parallel resistors that can be put together to make a 50 ohm load at almost any wattage level. If you start with 'small' wattage resistors, you'll end up with a huge 'glob' of them for high power. Just depends on how 'high' power you want to get. Once you get the value of resistance and wattage you want, just dipping that 'glob' into a bucket of oil for heat transfer is a lot easier than trying to mate them to a metal heat sink. I think I'd tend to just buy that dummy load rather than build them, it's just easier, and probably not that much more expensive when you're finished. But then, you may be able to find cheaper 'parts' than I can. If it's a matter of you wanting to build one, great, have at it. The 'biggies' are that the resistance needs to be as close to 50 ohms as you can get it. And, the wattage should be -MORE- than you'll ever need (twice as much is nice). After that, it's just a matter of whatever you can 'glob' together. Sort of.
- 'Doc

 

[Robb]

You see; I have a place called 'Hal-Ted Elctronics' that carries a lot of the overflow and no longer used materials from all of the semiconductor industries in Santa Clara County. You all know it as 'Silicon Valley'. They are one in the same. So when I need parts to fix or make something, I have to drive abouit 5 miles to get there. They dont have everything; but whatever they do have - it is pretty cheap!

You can always buy those resistors online pretty cheap if you cannot find them around your own town. I just wire the four resistors in parallel and solder them to the male PL-239 connector. No mess; no fuss - as easy as that...

 

[wavrider]

Four 220 ohm 2 watt carbon resistors in parrallel, 8 watts at 55 ohms.

Eight 440 ohm 2 watts resistors in parrallel, with a switch dividing the set of four.

Switch open you have 110 ohms, pretty close to 2:1 swr, close the switch and 55 ohms. Pretty close to 1:1 give or take.

Surplus sales of Nebraska.
RF Parts.
Mcmaster -Carr
Moyer electronics,
Mouser
Digikey

Just a few places to look for carbon resistors.

 

[Marconi]

James, concerning your Imax. I looked at some of your pictures and noticed that your antenna is very close to your roof with or without the GPK attached. I find that the Imax and A99 among others does not perform well when the base or the tip of the radials are close to anything. This may be why your match is a bit high and as you note moving the rings did not seem to make much difference or fix that.

At what frequency were you trying to tune your Imax?

A similar problem with an A99/Imax happened to me also, but at the time I could not raise my antenna higher to get it away from the roof, so I moved it farther out in the back yard until it was clear of stuff and that made a difference in match and a lot of difference in performance. I also noticed that when I got the full antenna well above the highest peak on my roof that I was no longer seeing the attentuating shadow affects on the performance of the antenna pattern. In particular this was noted to stations located on the opposite side of the house from my antenna.

My particular Imax shows and SWR of less than 1.4:1 from 25.855 to 28.105 mhz using my Autek VA1 analyzer thru a 68' feed line. As you noticed in your BW test using an inline meter, the bandwidth curve will look almost totally flat in the range of the rather small CB band where you tested. So, you can't really tell much using an inline meter on this antenna with a <2.0:1 bandwidth covering over 4> mhz of total bandwidth.

My particular Imax shows an SWR of 1.1:1, from 27.005 to 27.655 mhz on my Daiwa CN801 inline meter. It has not been cliabrated either, so it is what it is. I do see higher SWR readings with other antennas, so I know it is working and is close enough for government work.

I also find that the antennas Field Strength is max when the rings or finely tuned near the center of the threaded range for adjustment and the antenna is at or very near resonance.

My Imax manual shows the antenna is supposed to be truely resonant at 27.205 mhz, but my experience is different and shows to be resonant at 27.505 mhz with the rings in the middle as it comes from the factory. This may also be why you saw the best SWR higher-up in the CB band.

For me, the Imax bandwidth is so wide that the SWR differences you mention are of little importance to the results you are seeing. IMHO, your problem is the antenna is too close to your roof, period and if you fix that you should see the SWR drop to almost flat on your inline meter.

 

[cominatyalive]

4 birds with one stone,

Hello Gramps,

Sorry, but the pictures do not do my antenna height any justice at all. Yes, it seems by a few of the pics, or maybe all of them, that the antenna is low. But in reality, it is sitting on top of a 10' mast plus a 3' tripod. In my earlier post somewhere I did specify the heights.

http://www.worldwidedx.com/cb-band-...nnels-row-every-4th-channel-clear-bell-2.html

(Quote:The code for the FCC states that Antennas cannot be higher than 25' of the tallest point of your roof or house. My highest point of the house is 25'. My mast is 10" and my antenna is a whopping 24'. Ok, so I'm over the limit by 9 feet. Big deal, Like I'm the only person for miles around here with a CB antenna,.

25+10+24=59 And I got that last extra foot to make it 60' exactly by raising my mast a foot up in the tri-pod. Lord forbid that I was shy just one foot mind you. I would try moving my antenna to another location on my roof, but all other four quadrants of my roof are 4 or 5 foot lower than the middle of my roof. Plus, my house is narrow from side to side, but very long from front to back. It's an 104 year old, double story house. So I'm not moving it because of those issues. End of quote).

Sorry for the height illusion, but believe me, I have to stand on the very last rung of my 5' ladder just to be able to reach the GPK bracket. The antenna is 60' tall at the tip.

Per the SWR, It has been better at 1.2:1 on most of the upper channels, and 1.3 to 1.5:1 on the lower 7 channels or so. I still have the tuning rings pretty much towards the top of the threads. Anywhere downwards & my SWR shoots back up to 1.4:1 on the last 20 channels, and 1.5:1 on the lower 20 respectively.

It is so hard to take pictures of the height because I have a double story house, 25' tall at the crest and the houses & trees keep me from getting a justifiable height shot. When the snow melts, I will go back up & take pictures at eye level of the mast & the bottom of the antenna, etc.

I tune my SWR at channel 20, midway of the 40 channels. But I have heard of people tuning on the frequency they use the most. I have thought of doing that, but I really don't have a special channel yet. There are a bunch of guys on Channel 10 in Kenosha WI who talk every night, but it's just so hard to join their clique. And with all the swearing sometimes, I do have second thoughts. Sad eh?

But yes, you are absolutely right, anything below 1.5:1 and they say one should be very grateful. But like many, I'm a twit.


I will eventually get more into the tuning aspect of this antenna like you have, but right now as you can see, I am learning. I talked to the tech at Magnum Radios this morning and with all the static & interference from the neighbors Electrical, underground drop, he advised me to go with a Horizontally polarized antenna such as a Yagi 3-element beam. Or any beam for that matter. I'm going to do it in the spring, but I still want to keep my IMAX too for giggles. But really, I really do not know for sure what I will do yet exactly. A beam, I'm sure, has it's ups & downs as well. I've been a readin!




Hey Wavrider,
I really dig the switch thing! pretty clever, the best of both worlds!
I already purchased a few resistors though from Discount Electronic Components – Tedss.com.
I am going with Qty 3, 300 Ohm, 5 watt carbon composition Resistors.

100 Ohms at 150 Watts power handling. I am also thinking of using the Paint can method with mineral oil.

I went with the rounded # of 300 Ohms so I would have exactly a 100 Ohm, 2.1:1 calibration. But as you all know, there is always that + or - 5 percent leeway with most common resistors.

But as hard as it was to track down a few resistors, one has to take what one can find!

Thank you for the idea though and great job!

Thanks for the store listings also, I will write them down. Muchos Gracias!


Hey Rob,
I will have to check out that place you buy from as well. TY for the tip.
Yes, and one can even wire these resistors in series as well and just use addition instead of division. But I like the Parallel method the best. Yes, I have heard of Silicon Valley, and I'm envious of your location. Must be warm all the time & good reception maybe? I can't recall without going back to previous threads if you mentioned anything about if your reception was ok or not. I'd die to get away from the 15' foot house spacing like the way it is here.


Hey Doc! ya know what? you are correct. One might as well just buy one. But the one's I saw, looked cheap & had low wattage. I heard they burn up after some time. Yes, a heat sink is pretty much out of the picture if one is going to dunk them anyways. But I'm still going to solder the ends to a Brass or Aluminum thin plate anyways for stability. Yes Doc, I noticed too that anything over 5 Watts and I was S.O.L

I bought some 200 Ohm 3 watt resistors also while I was at it because of their $25.00 minimum purchase. Geez. Yeah, we all know how that feels, :bdh:

Thank you for your kind input.
Every little bit of info is always appreciated by me.




James

 

[cominatyalive]

Gramps,

Oh yeah, I almost forgot to tell ya,
I wasn't actually looking to tune my Imax. As most always, as everyone knows,
they all come around 1.4:1 out of the box.

This all started when I started suspecting my that my PAL KW-1 SWR/WATT meter was giving me false wattage readings. And I think it still is. I then began trying to improve my SWR as well while I was dabbling.

At first, I did not know how to go about first checking my PAL meter's SWR calibration. That's why I am looking to use a home brew dummy load.

I just got side tracked that's all. I still have to figure out what's going on with my PAL's wattage reading. So I went and bought one of those (Workman SWR/Watt/Field strength) meters for $20.00 to see if the wattage reading was the same.

My PAL's reading is always 10 Watts on the money with my Zachary T. 40 channel base. The Workman meter says 4 to 5 watts. Which is more understandable. But this leaves me guessing. So hence, the dummy load.

Does anyone know how to go about checking the watt meter on a PAL KW-1 meter or any SWR/Watt meter for that matter? I'm thinking someone before me had the PAL tuned to a Ham radio or something. It's in fairly good shape & you can view it in a few of my pictures in my photo album in my profile here. Can a certain dummy load be made to calculate or calibrate wattage also?


In the meantime, I will scour WWDX for previous threads on this if any & look around the Net as well for answers.

TTYL

J.

 

[WA2FDU]

Greetings All.............

I just received my IMAX 2000 with GPK yesterday. Thanks Honey!!!!

My main interest is for use on 10 meters, centered around 28.450(ish). I understand that out of the box it is pre-tuned for 27.205.

I have read where folks were able to shorten the antenna approx. 11 inches to raise the centerpoint close to that area. Unfortunately I have not been able to find any charts, to use as a guideline, that may have been created by users to support this. I do not have a analyzer available.

My goal is to get it as close as possible physically and then tweak it from there. Up to 100 watts I would use, if needed, the internal tuner in the TS-2000 and then above 100 watts I will be using the Palstar AT2K.

Who out there did shorten their antenna?
What's the 'Proper' way to shorten the antenna?

Any and all advice would be greatly appreciated.

Merry Christmas to all and to all a good cycle 24

Stephen / WA2FDU

 

[Robb]

Welcome to the forum WA2FDU!

I would check it on the 10 meter band before you cut it. I read somewhere today, that this antenna is most resonant -stock- around 27.500mhz-ish. I just checked my SWR on that freq, and it was practically flat. This antenna is known to be good across 3mhz wide at a 2:1 VSWR. So you should be good to go on 10 meters. I just checked my SWR on 10 meters/28.405 and I had a 1.2 SWR.

So unless you want to mess with a sweet 3mhz usable bandwidth - go ahead. I use mine all of the time on 10 meters and I haven't altered mine one iota. Works great out of the box. There may be better antennas - but it pretty darn good for what I paid for it. I wouldn't trade it for any antenna in its price range - or beyond. Maybe a Sirio Vector 4000 would be better. But it is built too delicately for my taste; but it is greater antenna.

Some Hams have claimed that it will work all the way up to 20 meters with a tuner. I don't know about that personally. Up to 15 meters - yes. Best between 10-11-12 meters