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Author Topic: HF mobile antennas that handle power  (Read 6551 times)
W3LK
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« Reply #15 on: February 27, 2011, 12:25:14 PM »

I gave it to a friend in Kerrville, TX to replace a very old High Sierra. Its problem was the contact ring assembly, a major drawback they have never redesigned.



I'm curious what this 'major drawback" you refer to is. My 1800Pro is over 10 years old and I have had zero problems with the contact ring assemble, or any other part for that matter. I am still using the one that came with the antenna originally.
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K0BG
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« Reply #16 on: February 27, 2011, 01:11:14 PM »

I've heard your comments about your HS before Lon, but I get enough e-mail about the problem to make me wonder.

I have one in my possession as I write this, and I'm fairly certain it is an 1800, but it might be a 1500. The owner bought it used, and he says it's about 12 years old. The weather cover looks like a few limbs have smacked it. From what I can see of the contact ring, it looks well worn, and it is intermittent. I have taken it apart yet, as I have two other projects to complete. If I can remember to do so, I'll let you know what I find.

My biggest complaint, is the same one I have for the some of the Tarheels. The matching coil is mounted inside the mounting bracket. In some cases, that makes adjustment a pain in the rear. If I install one for someone else, that's the first thing I change.
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W3LK
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« Reply #17 on: February 27, 2011, 03:44:47 PM »

I am having a hard time getting my head around the "intermittent" bit. The spring makes 360 degree contact on the coil for at least two full turns. Can it happen? well, is someone says they are having a problem, then I guess they are, but I have talked to many more Tarheel owners at hamfests who make the same complaint about the finger stock in their antennas.

So, which one is the design fault that needs correcting?

FWIW, the antenna is on the third vehicle and I have never found any particular problem getting a good match with the coil in the mount.

Personally, if you gave me a Tarheel (or the MFJ variant) I would give it away. It's called personal preference. Smiley
« Last Edit: February 27, 2011, 03:47:10 PM by W3LK » Logged

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K0BG
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« Reply #18 on: February 28, 2011, 07:16:01 AM »

Tarheels have the same problem if they're used a lot because the contact material isn't beryllium copper. Whatever they use, wears off whatever coating they have.

I've seen several screwdrivers that have been used so much, you can see where each contact rubs against the coil. I suspect the clime you live in has as much to do with wear as anything. There is one make that uses a seal coil assembly, that tends to fill full of condensation. Talk about intermittent!

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W3LK
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« Reply #19 on: February 28, 2011, 01:14:42 PM »

As you know, HS uses a stainless steel spring for the contact medium. The spring fits into a milled channel in a collar that fits around the coil. It is virtually impossible to have an intermittent contact, as the spring is slightly compressed when in contact with the coil. There is nothing to break off, like one has with finger stock. Even if the spring breaks, there is nowhere for the pieces to go, and the spring is still in contact with the coil.
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K0BG
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« Reply #20 on: February 28, 2011, 04:15:06 PM »

Lon, I am well aware of how the antenna is made. Over the last 3 or 4 years, I've worked on several, and installed several more. Most of the time, they work well. Even when well used (lots of band changes), they hold up pretty good.

There are a few other things that happen, and I can't say with certainty if I've seen it on a HS or not. Most well-made screwdrivers have enough clearance to keep the unused portion of the coil away from the insides of the mast (not all, but most). If the screw gets worn, or the attachment method wears or comes loose, it is possible for some portion of the unused coil to come in contact with the inside wall of the mast. This results in a shorted turn problem. While the coupling is capacitive, there is still some reduction in the Q factor of the coil, depending on the length of that portion of the coil still inside the mast.

If the coil assembly get worn, for whatever reason, the coil gets "sloppy" as it transverses the mast (when changing bands). If this allows the bottom end of the coil to touch the inside of the mast, the result appears just like an intermittent; the coil contact assembly's design notwithstanding.

Not too many will agree, but if you want the highest Q possible, the coil must be of the exact reactance needed, with no shorted, or capacitively loaded unused turns. The trade off then, with any remotely-tuned HF antenna, is a slight, to moderate reduction in Q, which directly relates to efficiency. How severe that is, depends on a lot of factors, and not just the make or model.

I will say this. There is one screwdriver design which is so poor in application, it is a wonder the thing radiates at all! Can you imagine a "screwdriver" antenna wound with #22 awg? Yet, it outsells almost every other screwdriver type on the market.

Go figure!
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W3LK
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« Reply #21 on: February 28, 2011, 05:21:42 PM »

I haven't had mine apart, but Jim Heath had a cut-away of the 1800 at the Baltimore Hamfest a few years ago and there is no way that I can see that the coil can come into physical contact with the mast. Even with the coil fully retracted there is several inches clearance between the bottom of the coil and the motor assembly.

I'll just say that I've never personally met an HS owner, and I know a few dozen of them, that has ever bailed out on them for a Tarheel or any other brand. I know lots of folks who have bailed out of other brands for HS, though. Smiley

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K0BG
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« Reply #22 on: March 01, 2011, 10:27:17 AM »

Part of the issue has nothing to do with the brand, per se. Everyone thinks the great advantage of a screwdriver is the fact the turns aren't short tapped like they are on a HiQ for example (it has its own set of problems). Therefore, the Q of the coil remains high, but that isn't the case.

First, the coil is short tapped, but it is due to capacitive coupling, rather than hard wired so to speak. And, the large mast needed to contain the coil also reduces Q because it is within the field of the coil.

If you disassemble some of the poorer designed units, you often see burn marks toward the bottom of the coil. This is caused arcing from the coil, to the inside of the mast (flywheel effect as they say). It is exacerbated by poor contact assembly design. You really can't see it with an ohmmeter most of the time, but you sure can see the results. I've had an MFJ unit apart (Ameritron, whatever), and have seen the results of arcing. And as I said before, I've seen one HS that showed signs, but I really don't know which model it was.

I can't think of any HF mobile antenna which doesn't have some drawback; that's a given! But when they have a bunch of drawbacks, you begin to wonder why folks buy them. Must assuredly, the one with the most drawbacks is the Yaesu ATAS. Yet, owners seem happy, and it is the largest selling, remotely tunable HF antenna in the world. Go figure!

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N5UD
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« Reply #23 on: March 05, 2011, 12:16:45 PM »

"If the coil assembly get worn, for whatever reason, the coil gets "sloppy" as it transverses the mast (when changing bands). If this allows the bottom end of the coil to touch the inside of the mast, the result appears just like an intermittent; the coil contact assembly's design notwithstanding. "

I have seen the same problem at the top end of some screwdrivers. The exposed coil makes contact with the mast, in addition to the contact ring still lower down in the mast.

What's wrong with the HI-Q coil ?

Dave N5UD
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K0BG
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« Reply #24 on: March 05, 2011, 03:06:06 PM »

Two things.

In climes where there are large variations in temperature (North Dakota, is a good example), moisture condenses inside the coil with predicable results. On the higher bands, you sandwich the remaining coil between the aluminum shorting plunger, and the aluminum end cap. If the whip is long enough (CB whip), the losses are rather noticeable on 17, and above. The condition is exacerbated if a cap hat is used, especially one a foot or so above the coil.
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N5MOA
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« Reply #25 on: March 06, 2011, 08:54:45 AM »


Everyone thinks the great advantage of a screwdriver is the fact the turns aren't short tapped like they are on a HiQ for example (it has its own set of problems).


Not even close to everyone. I see no advantage to a screwdriver antenna. Antenna length changing with the bands is a dis-advantage to me. The potential for the coil to contact the mast, other than where it is supposed to contact it, is a dis-advantage to me.



What's wrong with the HI-Q coil ?

Dave N5UD

I don't have any degrees, or test equipment, but I haven't found anything wrong with it. It is a much better antenna, imo, than the screwdrivers I've used. A bug catcher is close to "as good as".


Two things.

In climes where there are large variations in temperature (North Dakota, is a good example), moisture condenses inside the coil with predicable results. On the higher bands, you sandwich the remaining coil between the aluminum shorting plunger, and the aluminum end cap. If the whip is long enough (CB whip), the losses are rather noticeable on 17, and above. The condition is exacerbated if a cap hat is used, especially one a foot or so above the coil.

What is a "large variation" in temperature? In Texas, it can vary 40 deg (or more) morning to afternoon, winter or summer, and I haven't noticed  condensation in 3 years of use. Certainly not enough to cause a "predictable result", whatever that is.

How did you measure the "noticeable losses" on 17m and above? I use a 84" whip on mine, and in A/B checking against my vertical or dipole, I'm not seeing it.


Quote from: K0BG=topic=73630.msg499173#msg499173 date=1299004037


I can't think of any HF mobile antenna which doesn't have some drawback; that's a given!



They are all compromises. It comes down to how much compromise your expectations will allow.

73, Tom
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GOLDTR8
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« Reply #26 on: March 06, 2011, 02:28:17 PM »

Per the original poster question for a recommendation on an antenna to handle power that is a screwdriver type.  I recommend a scorpion antenna.  I own one on a jeep and it is a well built piece of equipment.

With this antenna you would not have to worry about putting the power to it and not get damaged during mobile running.


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WX7G
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« Reply #27 on: March 10, 2011, 05:46:56 AM »

I subject a Tarheel 200A HP to about the maximum electrical stress one would in amateur use. Ground mounted with a low resistance ground means maximum antenna current. 1200 watts on CW with no problems. The only harder use would be RTTY.
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W9PMZ
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« Reply #28 on: March 10, 2011, 06:28:44 AM »

I have been using a Hi-Q 3/80-RT now for 2 years.  The manufacturer claims that the coil housing is sealed.  I live in Ohio where the temperature can change by 40F in one day and I have never noticed any condensation.

The problems that I have had with "condensation" are mostly due to snow and slush caking on the mount...

It seems to handle the SG-500 (500w) with no problems.  Just purchased a Hi-Q 4/160-RT and can't wait to try it!

73,

Carl - W9PMZ
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N6AJR
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« Reply #29 on: March 13, 2011, 01:05:33 PM »

The origonal screwdriver the DK-3 are still available now and then used, and the tend to handle a bit more power, but as Mr. Don Johnson  his self said, "no sense having an amp on hf mobile as you can't her farther than you can talk with 100 watts." or in other words , all power does mobile is turn you into an alligator, , all mouth and no ears..."
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