Interesting results with the IMAX2000

For about the last two years now, I've been running an IMAX2000  at about 35ft for working 6m-20m. This is one that was made before Solarcom bought them up. This version is 26ft tall whereas the more recent Solarcom version is made a bit smaller, at 24ft, so as to be able to ship the things more cheaply, at the cost of some performance. 

I should explain how I happened to get the thing. I've been running a local net on 10m for the past couple years, now. One weekend, we had a storm come through and wipe out the 40m end fed I'd been using.  Part of an old tree came down on it. I needed something in a hurry to allow me to run the net that night, and so I jumped at an offer made by a friend here locally for the IMAX for $30 bucks. I had only intended for it to get me out of the immediate troubles, never dreaming I'd be keeping it in the air as long as I have. I immediately started getting fabulous signal reports. (What the bleep are you running?)  It's a stone fact that a lot of the guys around the Rochester area started snapping up IMAX antennas once they heard me using this one.

Yeah, I know... A CB antenna?

Yep, and likely this older design is the best kept secret in Ham Radio. Indeed;  I'll tell you flatly, it's the best 10m omni antenna I've ever used. And well, my logs speak loudly to the validity of the design... with well over 5000 QSO's, all 50 states and 138 countries in those two years.

Here's the deal; At 10m it's a .64, which is as large as you can get in a vertical, without the pattern collapsing on itself, With 100w in on 10m from the 991a, and it's 5.2db Gain,  the numbers say I'm getting just shy of 400w ERPi, and somewhat less on the other bands. (350 if you subtract the losses of the LMR400 I'm feeding it with. ) I'm using 20ft worth of aluminum mast which I immagine provides aply counterpoise, which in turn keeps the radiation agles appropriately low for groundwave work and gives me an edge when DXing. I suppose the ground-plane kit would do even better but I've not managed to locate one, yet, and anyway, I'm unconvinced it wouldn't affect it's abilities outside it's designed bands.

In the process of the A/B comparison with the new tuner, I've left the antenna's tuned resonance point at around 27.800MHz, which allows me to run 15m, where the IMAX is a perfect half-wave, perfect match, no tuner needed, and still respectable gain.. 12m is also "no tuner", giving about a 1.7 match, though of course I use the internal tuner on the 991 to touch that up. On 17m and the bottom of 6m, I can handle also with the my Yaesu 991's internal tuner.   Past that, say, 20m, and 30m, an external tuner is required.

I had been using an MFJ 941b tuner until recently. The Inductance switch was giving out, however, (the shaft, where it intersects with the switch plate was loose... I gather this is a common problem.)  I decided it was time to upgrade, I managed to find a used MFJ Versatuner II (MFJ-969) at a local Ham Fest.

One of the first things I attended to with the new tuner was to put it through it's paces at the ends of the coverage the 941 had given me. The 941 was able to tune the IMAX to resonance at the transceiver on 20m with some effort, but no lower, and up to about 51 MHz on 6m, but no higher. Now, the antenna itself is also tunable to the extent of around 1MHz, but I left that alone for the purpose of keeping the comparison apples to apples. Besides, I didn't want to mess with the results I'm getting on 15m.

I found with the new VersaTuner that it would tune all the way down to 80m, but performance really starts falling off below 20m. 30m is marginally useful when the band is open, but the performance isn't really satisfactory. Even on 20m I reckon there's about a 6db loss in efficiency, so I can only imagine what it is down below that.

My assumption is that the loss of performance would be even steeper if I were not running very low loss  feed-line to it, given the amount of power absorption in, say, 8x when presented by a high actual SWR.

The amusing thing about this is the reaction I get from the folks on 20m when I tell them I'm running 100w into a CB antenna.

So, two conclusions: 

One: The IMAX stays where it is.
And two:The new tuner, aside from needing to clean up the inductor rollers a bit, was worth the $100 I paid.

End Fed Half wave in Half Square config....

 

The End Fed Half wave in Half Square config?

 

That's a mouthfull!

Essentially, I'd planned on doing an inverted L, It turns out that I would need a much more substantial guy wire system to make the fiberglass poles stable in the config I'd planned on using.

 

That problem was the first thing I noticed when I pulled the instruction manual out of the box containing the 46ft of fiberglass pole.

(Rats, here we go again.)

 

Then I remembered a vid that Peter Waters put up about a year ago.

 

Consider the drawing, below, courtesy of Peter himself.

 

 

 

What we have here is two vertical 1/4 wave antennas held in phase because there are two quarter waves of wire in the top section that feed from one side to the other. This results in about 3db worth of gain over a single quarter wave with appropriate ground plane. That gain comes off broadside to the antenna. In other words, you're standing right in the middle of one of two strong lobes as you look at the drawing. In my config, that means SW/NE.

 

That alone makes this thing attractive to my situation, given I can't go "up" as high as I'd like. I'm less than happy with only about 18ft worth of height. (understand.... the antenna ends are raised about the ground by a foot or so). I am thinking that the poles should eb reasonably good at the much lower height and wind load. At this height, the thing models to a radiation departure angle of about 18 or 19 degrees, in my modeling. Not the 5 degrees Callum likes, but not too bad.

 

One trouble is, it only works on 20m, if you're planning on running current fed, to get your usual 50ohm loading.

 

But there's one more bit of magic I'd not considered until going over Peter's vid again:...

Note the voltage feed point, on the one end, left side. Attaching there will give you about 2250 ohms, which of course is perfect for my 49:1 Un-Un.... and what you have here, effectively, is a half wave end fed for 40m, which will work on 40,20,15 and 10m and likely be close enough for the tuner to get me on about everything else.

 

Glad I got the VersaTuner at the Roc City Fest!!

 

So, this will be the way I go for the time being.

Comments as always invited.

The culture of Ham radio.... past vs present

 Every group, be it a group of family, friends, a group of professionals, a group of Hobbyists, whatever.... in fact, group you'd care to name, has it's own Culture. (mini-culture, microculture, whatever you'd like to call it.)  Each group has their own way of doing things, their own values, their own way of doing things, their own way of speaking, their own value structure, their own  stories, their own metaphors, and so on.

 Add to this, there are subsets of each grouping..... that have their own mini-culture within a mini-culture. 

Ham radio is no different in this regard than any other such grouping of people. 

The purpose of bringing all this up is an observation that a goodly amount of friction within Ham radio circles these days, is caused by a perceived slight by one sub-grouping within Ham radio to another. 

Consider a recent conversation on QRZ, wherein I posted the following Video:

 

 

Now, I happen to think the operators in question did a pretty fair job at what they were doing; passing info about the event. But of course there are those who disagree"

"I am sorry, Net Control was distracted."
"QSL"



This is why they won't even let us borrow the keys to the clown-car anymore.

 

And...

 

No real net control and they all run over a guy asking for help. I am sure if you tell them they will get all wrapped up in being offended. 

One of these two goes on from there:

My heartburn focuses on overview of the style, substance, and discipline (lack-of) by all stations concerned.

Net Control sets the tone. The situation for which this communications circuit was activated is a tornado--potentially a catastrophic situation with safety-of-life implications. Yes, we're Amateurs, not professionals--I get that. But the comment "Sorry, NCS was distracted" is superfluous and has no value to anyone. A skilled communicator transmits "SAY AGAIN"--that's all. No one knows or cares why a message was lost.

Likewise, sorry boys and girls, "QSL" on Amateur radio is no more appropriate than "10-4"--which I'll bet you all a small Dunkin' Donuts coffee 85% of you folks would go beserk over when you hear it. But--sorry--QSL to me sounds like 10-4 to you. Totally unprofessional and out-of-place. ROGER is the procedural word.

There were indeed all kinds of Amateur nets of every purpose, only several decades ago, where squared-away radio communications procedure was practiced, utilized, learned and advanced; everyone involved took justifiable pride in their proficiency & efficiency.
Emergency Management entities welcomed hams' help because many of us had listening skills and communications chops. Perception has now become reality. No one wants us anymore--for cause. This emergency situation voice network sounds like an ordinary Tuesday Breakfast Club at the Rome Point Cafe, only on VHF radio instead of the corner table for 6.

In any structured, disciplined critical endeavor--Emergency Medicine, Maritime, Aviation, Firefighting, Safety of Life radio communications-- the philosophy is "We train like we operate and we operate like we train." When things get stressful and overwhelming, as in a real-life bad situation, humans 'default to primacy'--under stress we get knocked-down to what's baseline and normal behavior. That's why a good communicator works
towards being effective every time, sounding like he or she should, every time. You can't just turn it on when it's mostly been off.

I wonder if this guy understand just how petty he sounds.  As I told him:

If he was in fact at the EOC it was probably intended to keep the government authorities more informed than they would have been from routine police and fire patrols. At the least, they apparently accomplished that.

The assessment on the idea of net control being distracted seems to me a trifle unfair. If he's at the EOC he has doubtless got information coming in from every direction, not just the radio that we're listening to.

I've been in police dispatchers quarters when major emergencies were happening. For example, when hurricane Agnes came through back in, what, 72? Getting data from multiple sources simultaneously is more than a difficult job.

 

I didn't bother to respond to the rest, mostly because I doubt he'd have understood my point if I did.

Where is this attitude coming from? He's defending his own mini-culture. What we're seeing here is a modification of the "Not Invented Here" syndrome we so often see. It's the same issue as some operators as regards Digital Modes.... FT8 for example.  I regard these complaints, these attitudes with annoyance mixed with some degree of amusement, in much the same way as I regard Socrates bemoaning the end of civilization:

"The children now love luxury; they have bad manners, contempt for authority; they show disrespect for elders and love chatter in place of exercise. Children are now tyrants, not the servants of their households. They no longer rise when elders enter the room. They contradict their parents, chatter before company, gobble up dainties at the table, cross their legs, and tyrannize their teachers."

First, the obvious comment is that Socrates' complaints to the side, Western civilization didn't end, it was EVOLVING, and was so even then. 

Second, let's now tie this in with my opening comments on this post: The complaint about quality of operators is not a technical thing. It is a social thing, a cultural thing. The complaint is not that traffic is not being handled, that messages and info aren't going out, and being understood and passed on to the appropriate authorities. It's that the traffic didn't sound the way he wanted it.

As I said, petty. It's the same self-righteous indignation directed at those running FT8 and getting their DXCC in six months instead of 40 years,   It's the same self-righteous indignation directed at"No Code Hams", ARES members, REACT members, Emcomm enthusiasts, and essentially anyone that doesn't fit their mold.

 Sing it with me, Children...."It's Not Ham Radio,

Except it is, regardless of his liking it or not. 

I'm of the firm belief that the attitudes we see here are harming Ham radio, not helping it. 

I close with the thought that as Paul Simon once wrote: " Orangutans are skeptical of changes in their cages". I hasten to add that the average age of ARRL members is 69.5.  Get the picture?