Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: Prev 1 2 [3] 4 Next   Go Down
  Print  
Author Topic: Maxx-com tuner revisited  (Read 4393 times)
WB2WIK
Member

Posts: 20611




Ignore
« Reply #30 on: February 05, 2004, 08:30:14 PM »

My offer to de-pot one still stands.  I'll be happy to do it, and photograph and publish the results right here.

The formamide solution will *not* attack coils in any way, unless the coils are made of plastic!  Copper wire, which I assume would be used for any coils therein, comes out bright and shiny and looking just like the way they looked before potting.

WB2WIK/6
Logged
WA4HND
Member

Posts: 42




Ignore
« Reply #31 on: February 05, 2004, 08:53:15 PM »

I think it's a great idea.... just don't use mine!!!

 < G >.

Al
Logged
K0BG
Member

Posts: 9879


WWW

Ignore
« Reply #32 on: February 05, 2004, 10:24:29 PM »

Al, I think it was 1986, but if not it was close. The ARRL did exactly what Steve offered to do; unpot the thing. What they found was a resistor. As I recall, it was not 50 ohms, but 47 or something like that. This resistor was across the coax, and the output terminals were attached to each end of the resistor. If you look at the "box", you'll notice one is better insulated than the other. If you use it with a long wire or mobile whip, you ground one end (the shield end of the coax) and attach the other to the center of the coax. What you end up with is no more than a dummy load with a wire attached to the center conductor.

But let's not take this any further. I'll order one, and ship it to Steve who will unpot the thing and report back to you. Fair enough?

Alan Applegate, KØBG
Roswell, NM
k0bg@aol.com
Logged

WA4HND
Member

Posts: 42




Ignore
« Reply #33 on: February 06, 2004, 02:55:39 AM »

Well either they were playing a joke on the ARRL ( which isn't hard ) or they've changed the design.... I measured .2 ohms from center to edge of the so-239 and open between the center of the so-239 and the "hot" side of the ouput.   So no resisters there.... ( at least not directly. ).

If you take one appart, my bet is you'll see some coils or a transformer of some type.  In anycase, I busted a pileup on 20 today and got XF1K ( PAJAROS IS NA-166) on my second try from the mobile.... ( Not bad for a lightbulb <g> ).

I'm running over to Denver tomorrow so I won't be around here to defend myself <g>  Look for me on 14.300 in the afternoon.

73,
   Al
Logged
WB2WIK
Member

Posts: 20611




Ignore
« Reply #34 on: February 06, 2004, 02:13:08 PM »

When the ARRL does Product Reviews, they don't get the products from the manufacturers.  They buy them from retail outlets, just like anybody else: This is the Consumer Reports approach, and prevents having product samples hand-picked.

That's why you see them selling so much gear...a few months after the test, most of it is sold off to the highest bidder.

WB2WIK/6
Logged
AA4PB
Member

Posts: 12893




Ignore
« Reply #35 on: February 06, 2004, 04:41:58 PM »

When the ARRL does Product Reviews, they don't get the products from the manufacturers
-----------------------

In many cases they do. Sometimes their reviews even comment on how they returned a unit to the mfg for upgrades, etc. I think they often work pretty closely with the mfgs on the reviews.

From what I read on the MaxxCom page I believe that they have changed the design to include a broad band transformer of some sort. That probably improves the efficiency a little over what it used to be with a resistor directly across the coax and antenna. If you read between the lines a little, it looks like their transformer has maybe three windings. One goes to the coax, one to the antenna, and one to the resistor.

I sure find it hard to believe that MaxxCom intentially sent the ARRL an inferior product for evaluation. That would be pretty stupid! I could believe that they sent the ARRL a "special" unit that had the scrap electronics imbedded into the potting in an attempt to trick the ARRL into believing there was more too it that there really was. Fortunately the ARRL was smarter than that.

I admit that there are applications where a resistive loaded, broad band antenna may be a good choice. I think the MaxxCom prices are out of line however for what it is. They try to trick people into believing that they have discovered some new technology that defies well established principles. Anyone with any technical background can read their web page and tell that they are feeding you a line of bull when they talk about an antenna tuner causing the antenna wire to vibrate like a guitar string to generate the RF. I guess your transmit frequency changes as you tension the wire :-) I quite imagine that the only way you can sell a transformer and resistor for over $300 is to convince potential customers that there is much more to it.

TenTec sells a wire "V" antenna with a transformer in the center and loading resistors on each end. They don't try to hide anything. They tell you the resistors are there and even what value they are. They even provide a number of modeling plots and complete specifications for it.
Logged
N3ZKP
Member

Posts: 2008




Ignore
« Reply #36 on: February 06, 2004, 08:33:34 PM »

Al,

<< But if you're just talking HF... maybe you have never done any NVIS work... >>

Been there, do it all the time on MARS and other services and I have NEVER had a situation (exercise or actual disaster) that required split second band/frequency changing such as you describe.

As for "all in one" rigs, they have their place, but for real disaster work I prefer separate HF/VHF/UHF rigs and antennas that allow me to work multiple bands at the same time. Virtually every EOC, permanent or portable, ham-centric or government run, that I have ever been involved with over the past 30 years has operated on this same principle.

You prefer your theoretical scenerio, I prefer my proven in-actual-use scenerio. To each his own. Smiley

Lon



Logged
WA4HND
Member

Posts: 42




Ignore
« Reply #37 on: February 06, 2004, 11:51:24 PM »

>>Been there, do it all the time....

Yea, we know hams like you.... always have the last word... it's not right unless you thought of it.... and unless you agree it's wrong.   Bottom line you're not willing or able to learn new things or accept new concepts.

You know when you do split band digi work...  or synced freq hops, you do need split second band / frequency changing which requires very wide band ants.  Don't know why I'm telling you this, that system has been around for 40 years or longer...so I'm sure you've done that also <g>.

I'll leave you with this comment and do not expect me to reply to any more of _your_ messages...   hams like you give the entire community a bad name.  Ham radio used to be a place to experiment and try new things.  It's tuned into a community of "know-it-alls"... it's too bad.

I come up here to share info and end up trying to inform people who "have been there... done that" but don't even know what's in the box <g>.


Yea, all our EOC's have multiple radios, my jeep has the 587, a 742 tri-band and a few other motorola radios for special use.  The odds of me needing to transmit on UHF / VHF with the hf ant is.. (very low ) but guess what. I will be able to do it if I need to because I will have one ant system that I can attach anything to and have it work ( sure not as well as the tuned ants..but it will work. )

You go your way and I'll go mine... I have high standards and won't degrade this forum or ham radio by lowering them.

Al
Logged
WA4HND
Member

Posts: 42




Ignore
« Reply #38 on: February 07, 2004, 03:48:36 AM »

Lon, et all

The following is part of a post over in tower talk.  ( it wasn't posted by me but maybe this will help you all understand ).... well, except for Lon,  I'm sure he already knows all this <g>.

>>
 The Maxx-Com was originally designed for matching
marine antennas, such as the backstay of a sailboat
with waves crashing over it. It may be inefficient,
but I don't know of any other tuner that can handle
dynamically changing loads like that.
>>

In any case... it's food for thought.  Sometimes the goal is to __communicate__ .... not be ticked off cause you only got a 5 over 9 and your bud got a 10 over <g>.

The maxx-com pr says  you loose about 20 percent over a tuned ant.  ( From what I've seen so far I'd say it's more like 20 percent from uhf to 20 ) and 30 percent on 40 and 80.  Of course that's with my whip and I bet I can impove that by going to a longer whip.

But.... let's just say for argument sake that the thing looses 50 percent!!!  Ok, I'm running a power cube.... it puts out around 400 watts (worst case )  I've seen it go to 600 but I don't drive it that hard.... so lets say 400 and 50 percent... that means if I have to use the maxx-com, I'm down to 200 watts  to the wire.... if you had a screwdriver freeze up or an SGC fail to tune... or need to talk on a freq you don't have a coil for.... wouldn't you rather have 200 watts going to your ant rather than nothing?  If you can't understand that logic, there's no point in going on from here.


Al
Logged
N3ZKP
Member

Posts: 2008




Ignore
« Reply #39 on: February 07, 2004, 10:26:15 AM »

Geez,

Do you do a personal attack on everyone?

I simply pointed out that your scenerio for instantaneous band switching didn't match the real world of disaster communications.

I never said my way was the only way; just that it is what the overwhelming majority of professionly-run EOC use.

If that offends you, then that is your problem, not mine.

If you ever make it to Baltimore, give me a call and we'll sit down at my place over a piece of pie or a crab cake and discuss it some more.

Lon
Logged
AD5X
Member

Posts: 1432




Ignore
« Reply #40 on: February 07, 2004, 11:38:55 AM »

Maxx-Com claims 80% efficiency or better.  But you've said you are 1-2 S-units down from your SGC-tuned antenna.  That's quite a difference.  

Why not take the output of your Maxx-Com through a power meter terminated in a 50 ohm load and see what the Maxx-Com loss would be into a resonant & matched antenna across the HF bands?

Phil - AD5X
Logged
WA4HND
Member

Posts: 42




Ignore
« Reply #41 on: February 07, 2004, 03:44:53 PM »

That may or may not work, based on how I _think_ the maxcomm works.   What I was thinking of doing this spring ( it's way too cold out now ), is doing some field tests at a friends place.  ( he has an ant test range )... that way we can see what's getting into the air FS wise and what the pattern is etc etc.

Remember the output of the maxx-com is not an so-239... it's looking for the ant to start right there.... so an inline meter will most likely not tell the the entire story.

I'll report back later this spring to let you all know... but right now in Colorado... it's too cold to enjoy this type of work <g>.

Al
Logged
KA5S
Member

Posts: 229




Ignore
« Reply #42 on: February 08, 2004, 12:55:48 AM »

I remember the Maxcom review. IIRC QST said they'd found some surplus PC boards inside, apparently to make it look like a sophisticated device if someone opened it.

So ... they SHOULD have changed. Nowadays, these could even have an an isolator (circulator sending all the reflected power to a dummy load). Could be almost arbirarily complex -- and still not do better at antiresonance than a dummy load.

I've used TMC echelon antennas and also the B&W version.  I don't, now. END-terminated antennas however have a radiator that can work all the time. The B&W end-terminated obtuse V - otherwise known as a half rhombic - is one exanple. Military terminated fan-dipoles use resistors to keep impedance excursions to manageable levels. And of course the traditional terminated rhombic throws away half the incident power, all the time. These antennas' radiating elements carry substantially more RF current off resonance than a simple dummy load across the feedpoint gives - transformer coupling or not.

Whatever you get, you pay a price. And, size matters.

Cortland
Logged
KA5S
Member

Posts: 229




Ignore
« Reply #43 on: February 08, 2004, 01:02:50 AM »

Al, at the Pacificon HF-Pack antenna shootout a couple of years ago one person brought a short whip connected to a 5-watt, wirewound pot as a base inductor. It outperformed (not that it performed WELL, mind) a widely touted compact antenna with a toridal ferrite inductor at the base. Whoops!

All that glistens is not wet paint.

Cortland
Logged
WA4HND
Member

Posts: 42




Ignore
« Reply #44 on: February 08, 2004, 02:35:19 AM »

Corland,

And your point is what?  Why don't you go back and re-read ( or maybe read for the first time ) what we've been talking about here.  It's sure not small compact ants with a transformer feed.   Maxx-com's are normally used in the center of 100 ft dipoles or backstay marine use.  If they are used mobile, they are normally connected to _long_ whips ( and ribbon types like the SGC 303 work very well. ( even though maxx-com does not  think so <g> )

Now if you own a maxx-com or have direct knowledge ( by at least using one )... please feel free to contribute!!!

If not, all you're doing is commenting on "hear say"... or what you'd like to believe.... or maybe you just want to listen to yourself talk? <g>

Al
Logged
Pages: Prev 1 2 [3] 4 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!