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Author Topic: What Screwdriver Antenna To Buy And Why  (Read 18106 times)
K0WJ
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Posts: 2




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« Reply #15 on: August 12, 2010, 11:45:47 AM »

Don,
I personally would not want to be without my Scorpion antenna.  I have had a Hustler, a Hamstick, a Predator (fell apart) and a BB3.  None of these other antennas come close to the consistent performance of my Scorpion SA-680.  I also have an SA-6160 mounted in my backyard which I also use mobile during the winter months on 160.  As the saying goes, "You get what you pay for" - (just don't pay more than $100 for a Hi-Q).  The service you get from Scorpion is second to none and goes way beyond others.  The Scorpion also has a guarantee that no one else will match.  In addition, the manufacturer will stick with you through the installation process to ensure the best installation possible for your vehicle.  Nobody else does that either.

73,
Lon, K0WJ
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N5MOA
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« Reply #16 on: August 12, 2010, 12:52:36 PM »


One of the more interesting aspects of the shootouts is who wins on what frequency!? Some of the absolute winners on 80 meters, drop way down on 40, and disappear on 20 and above. Those typically are the ones with rather larger metallic end caps, like the HiQ, and Hustler large coils.




I'm using a HI-Q 5/160RT. I love it, works great. I bought it second hand a few years ago, and I have had nothing but good dealings with them. There was an issue with the motor lead (broke wire) and the reed switch  due to the previous owner hooking them up incorrectly (he hooked + to one side and - to the other). HI-Q was very helpful. Every manufacturer has "it's great/ it sucks" comments to deal with, and I don't care to get into a "he said/they said" discussion.

I'm no expert on mobile antennas, so I do have a couple of questions.

 Are you saying a properly mounted, efficient adjustable antenna won't be as (or more) efficient on 20m or 17m as it is on 80m? How so? I don't see that with my setup.

And what's the deal with metallic end caps on the coils? If I'm looking at the pictures correctly, isn't the coil inside the lower mast on the screwdriver antennas? It's better to have part or all of the coil surrounded by metal than have metallic end caps?

73, Tom
N5MOA
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WX7G
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« Reply #17 on: August 12, 2010, 01:41:12 PM »

If the 7 MHz mobile shoot out measurements were taken further than 70' between the the TX and RX antennas they were taken in the far-field.

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W3LK
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« Reply #18 on: August 12, 2010, 04:58:18 PM »

I don't know how the shootout(s) under discussion were conducted, but I tend to put such events in the B.S. category UNLESS only one vehicle, radio, mounting scheme, etc., is used with the antenna being the ONLY variable. Multiple vehicles, radios and so forth introduce too many variables for me to take any results seriously.

In reality, there are probably more difference in quality of construction and durability than in actual, real-world performance.
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K0BG
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« Reply #19 on: August 13, 2010, 06:22:34 AM »

Dave, the excepted fringe of far field is 3 to 4 wave lengths. On 40 meters, that's a lot more than 70 feet. I refer you to the work Rudy Severns, N6LF, recently published.
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WX7G
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« Reply #20 on: August 13, 2010, 10:02:35 AM »

Because a mobile antenna shoot-out is a relative signal measurement it does not have to be conducted in the far-field. Measuring in the near-field does produce an absolute measurement error. But, this error is the same for each of the antennas. Therefore this error drops out of the relative gain measurement. The relative gain measurements are valid in the near-field.

When determining what is near-field and what is far-field we must state a number. That number is the absolute measurement error we will accept. This error is due to the ratio of E/H not being 377 ohms in the near-field and it is due to the wave front being spherical and not a plane wave (what we call a plane wave is really just a spherical wave so far from the source that it is essentially a plane wave).

I usually peg the acceptable error at 1 dB. This occurs at a bit less than one half wavelength from a dipole. So, 70' at 7 MHz is far-field for our purposes.
 

 
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N5MOA
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« Reply #21 on: August 13, 2010, 11:34:50 AM »


One of the more interesting aspects of the shootouts is who wins on what frequency!? Some of the absolute winners on 80 meters, drop way down on 40, and disappear on 20 and above. Those typically are the ones with rather larger metallic end caps, like the HiQ, and Hustler large coils.




I'm using a HI-Q 5/160RT. I love it, works great. I bought it second hand a few years ago, and I have had nothing but good dealings with them. There was an issue with the motor lead (broke wire) and the reed switch  due to the previous owner hooking them up incorrectly (he hooked + to one side and - to the other). HI-Q was very helpful. Every manufacturer has "it's great/ it sucks" comments to deal with, and I don't care to get into a "he said/they said" discussion.

I'm no expert on mobile antennas, so I do have a couple of questions.

 Are you saying a properly mounted, efficient adjustable antenna won't be as (or more) efficient on 20m or 17m as it is on 80m? How so? I don't see that with my setup.

And what's the deal with metallic end caps on the coils? If I'm looking at the pictures correctly, isn't the coil inside the lower mast on the screwdriver antennas? It's better to have part or all of the coil surrounded by metal than have metallic end caps?

73, Tom
N5MOA


Anyone have an answer/opinion/reason why?
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W9PMZ
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« Reply #22 on: August 13, 2010, 01:32:23 PM »

"If you look over The consistent winners are Scorpion, Predator, and Tarheel 200A, and in that order."

The "winner" is the person who make the best optimization of the installation.

I have used the following, HiQ 3/80, Tarheel 200A, a K4POZ screwdriver, a MFJ manual scredriver (yea really) and a Hustler mobile.

Comparing the antennas to the same installation, e.g. using the same mount, the antennas are listed in order of performance.  Although there is not much difference between the HiQ and the Tarheel.

But my opinion is that the HiQ is a better bang for the buck.
 
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W9PMZ
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« Reply #23 on: August 13, 2010, 01:47:16 PM »

For some reason my post got hosed...

"If you look over The consistent winners are Scorpion, Predator, and Tarheel 200A, and in that order."

The "winner" is the person who make the best optimization of the installation.  I'd wager that someone could install a Scorpion that could loose to a Hamstick...

I have used the following, HiQ 3/80, Tarheel 200A, a K4POZ screwdriver, a MFJ manual scredriver (yea really) and a Hustler mobile.

Comparing the antennas to the same installation, e.g. using the same mount, the antennas are listed in order of performance.  Although there is not much difference between the HiQ and the Tarheel.  I switched from a Tarheel to a HiQ because of weight and it is easier to remove from the vehicle.

But my opinion is that the HiQ is a better bang for the buck vs. efficiency.
     - the overall length does not increase when tuning for a lower band (better stability).
     - HiQ giant bayonet quick disconnects make it easy to remove the antenna.
     - the HiQ is lighter in weight.  This makes for an easier installation.

My only complaint about the HiQ is the motor lead could be heavier guage wire.  I managed to break it...

However, the Hustler is not that far behind and if you are willing to work one band at a time with good efficiency per dollar spent, they are a good comprimise.


73,

Carl - W9PMZ
 
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WX7G
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« Reply #24 on: August 13, 2010, 02:21:35 PM »

Now that I know the antenna shoot out at http://www.3905ccn.com/newsite/files/pdf/shootout-2010.pdf was conducted at 7 MHz it makes more sense.

My antenna range measurements show a 40 meter hamstick being 3 dB down from a Tarheel 200A. So, there is not a huge difference between a Hamstick and the very best at 7 MHz. In other words on 40 meters and above a Hamstick is a fine antenna. Reports of Hamsticks being dummy loads on these bands are in error. 80 meters might be another matter and I'll get around to comparing an 80 meter Hamstick against a Tarheel 200A sooner than later.

Graphing the 2010 3905 shoot out data is revealing. The Hamsticks hold their own against the Tarheels and the other screwdriver antennas. Here they are crudely plotted, with the left-most "other" being 0 dB below the winner and progressing to the right is inferior. Each tick or space is 0.5 dB.

HAMSTICK  -  ---    -  
TARHEEL     --  -   -        -
OTHER      -- -- -
« Last Edit: August 13, 2010, 03:11:34 PM by DAVE CUTHBERT » Logged
K0BG
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« Reply #25 on: August 14, 2010, 08:19:03 AM »

I don't agree with your assessment, Dave.

As Lon pointed out about the shootouts; the approach is not scientific. It's more of a subjective measurement scenario. Whether one is clearly better than another is only in the minds of the participants.

One also has to be careful using data from a modeling problem because of the ground loss calculating problems.

All this said, simple math will give you ball park figures of coil Q, albeit static. If everything else is the same (length, ground loss, etc.), one can easily show a relative difference. In fact, the data is already published in the ARRL Handbook.

As for the question about metal in the field of the coil.... Yes, the sleeve surrounding the coil does have a profound effect on coil Q. If you use Jack Belrose's technique for garnering such data, the effect is about 40% to 50% reduction. However, as long as the Q remains above about 200 to 250, one is hard-pressed to measure the field strength difference. However, once the Q drops below 150, the difference in field strength becomes glaringly evident. But, there is another issue. If a properly implemented cap hat is used (top of the whip), there is less reliance placed on the Q, as long as it hovers over ≈100. This isn't the case with the Hustler high power coils, and the HiQ series with their large metal end caps. In most cases, these coils operate very near self-resonance, and in some cases over it, which effects field strength in a very dramatic way.

To harken back to what Lon said, there are just to many variables to make a pat statement about field strength of one antenna versus another, mounted on diverse vehicles, to make even a WAG about superiority. This is especially true when the measurement technique is flawed and/or taken at only one TOA. 

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N5MOA
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« Reply #26 on: August 14, 2010, 07:44:30 PM »


As Lon pointed out about the shootouts; the approach is not scientific. It's more of a subjective measurement scenario. Whether one is clearly better than another is only in the minds of the participants.


We are in agreement on that.


As for the question about metal in the field of the coil.... Yes, the sleeve surrounding the coil does have a profound effect on coil Q. If you use Jack Belrose's technique for garnering such data, the effect is about 40% to 50% reduction. However, as long as the Q remains above about 200 to 250, one is hard-pressed to measure the field strength difference. However, once the Q drops below 150, the difference in field strength becomes glaringly evident. But, there is another issue. If a properly implemented cap hat is used (top of the whip), there is less reliance placed on the Q, as long as it hovers over ≈100. This isn't the case with the Hustler high power coils, and the HiQ series with their large metal end caps. In most cases, these coils operate very near self-resonance, and in some cases over it, which effects field strength in a very dramatic way.


This is where I get confused. This is a direct quote from your K0BG web site:

Digressing once again. It is not uncommon for antenna manufacturers to publish their static Q measurements, and apply them to the assembled antenna. The truth is, once the coil becomes part of the antenna's superstructure, the Q can drop by 60%, perhaps a little more. There is no practical methodology the average amateur can use to determine the dynamic coil Q. Bandwidth and SWR are meaningless in such determinations. From the second paragraph above; Regardless of what hype you read or hear, with few exceptions most commercial antennas have Qs in the 100 to 200 range. If a manufacturer claims otherwise, be very leery.

If most commercial antennas have a Q of 100-200, how do you keep it about 200 to 250?

Scorpion claims a Q of 410 for their SA-680. HI-Q claims a Q of 580 for their 5/160RT. Both are using a HP-4342A. Should we be leery of both manufacturers? I couldn't find if those claims were for just the coil, or assembled.

If there is "no practical methodology the average amateur can use to determine the dynamic coil Q", what are you basing your statement that using metallic end caps is worse than enclosing the coil in metallic mast on? How did you arrive at the Hustler and HI-Q don't have a Q that hovers over ≈100?


To harken back to what Lon said, there are just to many variables to make a pat statement about field strength of one antenna versus another, mounted on diverse vehicles, to make even a WAG about superiority. This is especially true when the measurement technique is flawed and/or taken at only one TOA. 


Another agreement.

I ask these questions because if there is a "better" antenna than the one I have now, I'll buy it. I've used hamsticks, bug catchers and the HI-Q I use now. Other than a picture, I haven't seen a Scorpion, so I can't comment on how they work since I've never used one.

Nothing I've read yet convinces me there is a better mobile antenna than the H-Q I'm using now.

I don't have test equipment to check antenna efficiency for myself. What I do have is a TS-480SAT in the house, and a TS-480HX I am running mobile. 500w, a log periodic, vertical, dipole and inverted-L antenna to chose from in the house. 200w and a HI-Q on my pickup. That's as close to an A/B antenna comparison I can do.

My test for my mobile antenna efficiency is, if I work a dx station from the house, on any antenna, I'll get in the pickup, pull out in the field, and try to work them mobile. Am I always successful? No. Am I successful a large percentage of the time? Yes I am.

 E4 on 30m-20m-17m. JD1-O on 80m. VQ9 on 17m. D2 on 17m. HV on 17m. A3 on 12m. VP8-H, South Shetland on 30m. 3B8 on 30m. 3B9 on 40m. FW on 17m. H4 on 15m. BV on 15m. VK9-N, Norfolk on 40m-20m-17m-15m. I won't bore you with the rest, and I know others, including yourself, have worked more while mobile. Does all this mean anything to anyone else? I doubt it, but it tells me my antenna is working pretty good.

All but three of the dx entities I've worked mobile (142) have been since January of '08. Not exactly a sun spot happy time, so it isn't all propagation, the antenna has to play some part in that.

So if there is a "best" mobile antenna, in my un-scientific opinion, it's the one I have now. It will take more than an antenna shoot out to convince me otherwise.

73, Tom
N5MOA


 

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WX7G
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« Reply #27 on: August 15, 2010, 06:15:06 AM »


So it looks like the consistent winners are Tarheel and Ameritron in a tie, then everyone else.
[/quote]

The Ameritron screwdriver antenna is actually a Tarheel.
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K0BG
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« Reply #28 on: August 15, 2010, 07:27:37 AM »

The Q of both the Scorpion, and HiQ were static measurements. That is, they were just laying on the bench, so to speak. As for the measurements; once the Q gets to about 400, the accuracy of HP-4342A falls quite a bit especially at the higher frequencies. And, I don't know the test frequency on either one, but here's what I do know.

The HiQ was measured with just the Lexan coil assembly; the end caps were not installed. The Scorpion was wound on its core of Delrin. Both have about the dielectric constant. I'd love to see the HiQ measured with the end caps in place. I think we all might be surprised.

How much the Q drops once installed in the antenna cannot be easily measured. The 60% figure is probably close for the HiQ (depending on which model we're talking about, and the frequency of operation). I suspect the Q drop of the scorpion is a little less, but I've never actually tried to calculate it.

My new VNA should arrive Monday, and some retesting is on the agenda. The results won't be all that close, but close enough under the circumstances.
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N5MOA
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« Reply #29 on: August 15, 2010, 08:15:39 PM »


So it looks like the consistent winners are Tarheel and Ameritron in a tie, then everyone else.

The Ameritron screwdriver antenna is actually a Tarheel.
[/quote]

I did not know that, thanks. 4 out of 9 shootout wins should give Tarheel the bragging rights, such as they are.



The Q of both the Scorpion, and HiQ were static measurements. That is, they were just laying on the bench, so to speak. As for the measurements; once the Q gets to about 400, the accuracy of HP-4342A falls quite a bit especially at the higher frequencies. And, I don't know the test frequency on either one, but here's what I do know.

The HiQ was measured with just the Lexan coil assembly; the end caps were not installed. The Scorpion was wound on its core of Delrin. Both have about the dielectric constant. I'd love to see the HiQ measured with the end caps in place. I think we all might be surprised.

How much the Q drops once installed in the antenna cannot be easily measured. The 60% figure is probably close for the HiQ (depending on which model we're talking about, and the frequency of operation). I suspect the Q drop of the scorpion is a little less, but I've never actually tried to calculate it.

My new VNA should arrive Monday, and some retesting is on the agenda. The results won't be all that close, but close enough under the circumstances.

Thanks for the info about them both being static measurements. I've never seen a HP-4342A, much less know how to use one, or how accurate it is.

The rest of your post confuses me again, not that it's hard to do.

Taking the Q number from HI-Q's site of 580 (I have a 5/160, that's the number I looked at) and a 60%(your number) reduction of Q  assembled, that leaves a Q of 232.

So again I'll ask: How did you arrive at your conclusion below


As for the question about metal in the field of the coil.... Yes, the sleeve surrounding the coil does have a profound effect on coil Q. If you use Jack Belrose's technique for garnering such data, the effect is about 40% to 50% reduction. However, as long as the Q remains above about 200 to 250, one is hard-pressed to measure the field strength difference. However, once the Q drops below 150, the difference in field strength becomes glaringly evident. But, there is another issue. If a properly implemented cap hat is used (top of the whip), there is less reliance placed on the Q, as long as it hovers over ≈100. This isn't the case with the Hustler high power coils, and the HiQ series with their large metal end caps. In most cases, these coils operate very near self-resonance, and in some cases over it, which effects field strength in a very dramatic way.



Is that a calculation on your part, or an actual measurement?



 I'd love to see the HiQ measured with the end caps in place. I think we all might be surprised.


Probably so.


73, Tom
N5MOA

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