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Author Topic: 102" whip with coupler -vs screwdriver ur tho  (Read 1761 times)
KA1YBS
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Posts: 11




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« on: February 16, 2008, 04:20:05 PM »

Hello fellow mobile hams,

Recently I have been building up a mobile setup consisting of an IC-7000, 102" stainless whip mounted on a cheap 2" Hustler ball, and an SGC 239 coupler. The ball mount is practically 'in the clear' and the base of the whip is unobstructed (ie. not down on a bumper), yes, nice rig, crap mount, I know, I want to IMPROVE, please read on!

I can work 20 - 10m. Coupler refuses to tune above 30Mhz (not designed to) and below 20m (probably too much HV potential on cheap ball mount/insulator and whip could be longer...

I'm happy to work several states and Europe in the last few days, but 20 is dead at night and I want to play on 40 and 80 meters, boo hoo!

SO, I've already got some great advice (K0BG, of course!) but I am still on the mission! I want to hear some more collective experiences.

I am faced with this: Buy an Icom AH-4 which some hams I talked to can work 40m with the 102" whip, and includes no-fuss tuning, safely without menus etc, but it may not work for my situation, OR...

I'm curious about screwdriver antennas, and their ability to work 80m and even 160m. If I cut the cost of the Icom tuner, and put it towards a screwdriver, what will I gain? Is it really worth it? I know I can hook an autotuner to the screwdriver (Better RF) so I can still be lazy (safe while driving) and use the nice TUNE button...

So, please share your experiences! Many Thanks

73
Tim
KA1YBS
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KO1D
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Posts: 386




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« Reply #1 on: February 16, 2008, 04:29:13 PM »

I run a Tarheel Model 75a "stubby" with a Turbo Tuner on my TS-480sat. This is a perfect set-up for me right now. I run 40 and 60m mostly with occasional forays down to 80m SSB. I have no trouble working stations on 40 or 60. I have noticed that this is not an ideal antenna for 80m. I may move to a HiQ 5" or even just get a separate Bug Catcher 6" coil someday for 80 and 160m mobile.

The screwdriver is by far the safest and best way to go overall. Which screwdriver should be gotten based on your needs and budget. Alan's web site is the ideal one to get some good initial thoughts but check out the antenna farms at hamfests or local club meetings and ask around as to what works best with the locals.

Dan S
KO1D
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ARCH
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« Reply #2 on: February 16, 2008, 05:42:02 PM »

I use the Better RF with a High Sierra 1800Pro and my IC7000.  I found it to be better than a tuner with a CB whip.  

160 meters mobile will pretty tough.  With 100 watts output you'll be lucky to radiate a 1/2 watt.  Screwdrivers that claim to cover 160 to 6 meters are dummy loads.

In any case, stick with a name brand like High Sierra.  
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KF6RDN
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« Reply #3 on: February 16, 2008, 08:20:44 PM »

Your coupler should work to 80 meters with a 102" whip.   I went through the same sequence, 102" mounted on trunk of car, mine was an SGC 231, I could tune to 160M while sitting still, and could actually hear stuff.  Didnt try working it, I doubt I would have been heard.

It was weak on 80 even.

Anyway, rather repeat what's said on Alan's website, re length of feed from coupler to antenna, bondings of at least major sections of car body if they arent, good ground etc.  Thee "cheapness" of the mount shouldnt matter as long as nothing is to close to make an arc, and it's solid.  I used a cheap RS mount.

So, my "part deux" since I wanted to run a few hundred watts,  I went to a HiQ 5/80 with an auto "tuner".  Tuner in quotes as the antenna, is obviously the "tuner" the auto runs the antenna up and down.  I find I have to specificy that as some ijit will invariably say "That's not a tuner!"..

Anyway, it does give you the requisite eyes on road.  My only problem was it was a little bit "fat" for the trunk material, and waggled.

So now I've gotten another vehicle and am just now setting it up..  Not there yet, antenna mounted, solidly, just need to bond the truck parts. And possibly rethink where I have it mounted..

 
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KF6RDN
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« Reply #4 on: February 16, 2008, 08:23:31 PM »

Further note - the tuner is the N2VZ turbo tuner.  If you use it with an amp you'd put it BEFORE the amp, and amp off whilst tuning.
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NZ4Z
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« Reply #5 on: February 17, 2008, 03:18:45 AM »

Granted....i'm still learning, but I do alot of research on the net, and I had a Tarheel Screwdriver. I did'nt care for the screwdriver due to one main issue, when I tuned for 80, the thing had to extend to the point I was scared to run the speed limit......it gets up there. But, after reading the reviews of the HI-Q, I was sold, I now have the HI-Q 5/160 stainless steel model. This thing is beautiful, it is more $$$, but read the reviews, you'll find the money. All the movement is in the coil, and our military uses them, so that should speak for something. And Charlie provides some of the best customer service their is. The other thing, Alan, K0BG uses one, and he is the authority of mobile radio..... check it out....  www.K(zero)BG.com

Good Luck

73

Steve
NZ4Z
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K0BG
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« Reply #6 on: February 17, 2008, 06:05:16 AM »

One consideration no one really thinks about, but assumes, and that is; what's efficient, and what isn't!

For about the umpteenth time, length matters! No matter the loading (base, center, etc.), doubling the length, quadruples efficiency, all else being equal. Adding insult, comparing a base loaded antenna, with a center loaded one is difficult enough without knowing all of the various parameters. However, if I had to choose between a base loaded antenna (whip and AH-4 in this case), and a shorty-type remote controlled antenna, I'd take the whip/AH-4 every time! They're so close in performance, you probably couldn't tell them apart, but the AH-4 can tune about 10 times faster which can be of benefit. What's more, it's sort of difficult to "break" a CB whip should it hit a low hanging limb.

There are two things you can try before you spend a lot of money for a slight increase in performance. First, increase the length of the radiating element. Even three feet makes a big difference (11 feet overall). Or, you can actually load the element with a coil to make it resonant on say 20 meters. You have to be careful if you do this, as the voltages are VERY high, and you have to make certain the self resonant point is above the highest operating frequency you intend to use.

Lastly, the reason the SG237 won't load the antenna on 40, isn't the coupler itself, per se. In fact, the impedance matching capabilities between it and the AH-4 are very close. I suspect it is some mutual capacitive coupling between the radiating element and the coupler.

Alan, KØBG
www.k0bg.com
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KF6RDN
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« Reply #7 on: February 17, 2008, 07:17:44 AM »

"I am faced with this: Buy an Icom AH-4 which some hams I talked to can work 40m with the 102" whip, and includes no-fuss tuning, safely without menus etc, but it may not work for my situation, OR.."

I forgot to mention, and Alan mentioned it kind of in passing, but the SG line and an AH-4 are so similar that replacing your SG with an AH-4 will likely NOT fix your problem, unless there's something actually wrong with it.

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W3LK
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« Reply #8 on: February 17, 2008, 08:58:06 AM »

<<  I did'nt care for the screwdriver due to one main issue, when I tuned for 80, the thing had to extend to the point I was scared to run the speed limit......it gets up there. >>

Any of the various motorized antennas, if PROPERLY mounted, will survive a lot more than normal highway speeds, even fully extended. In this case, a proper mount is NOT a mag mount, trunk lip mount or some other non-permanent mount. Like everything else, if you want top performance, do it right. Smiley

FYI, motorized HF antennas were originally designed for use on helicopters. At least one manufacturer sells more of his design to the military than he does to the amateur market.

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
K0BG
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« Reply #9 on: February 17, 2008, 09:12:22 AM »

I agree with Lon. High Sierra has sold over 20,000 antennas into the amateur market. There are others obviously, but if speed was a problem, we'd all know about it.

As Lon pointed out, mounting is very important both from a safety standpoint, and from a performance one. It has always amazed me, that amateurs will buy a remotely tunes HF mobile antenna costing over $500, and then mount it with a $30 magnet mount.

Alan, KØBG
www.k0bg.com
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KA1YBS
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« Reply #10 on: February 17, 2008, 02:30:19 PM »

Hello All,

Thanks very much for the suggestions and experiences!

At the moment, I am going to investigate the potential capacitance issue with my whip. I am also thinking about extending it to 11', much to the disapproval of my XYL.

It appears, after looking at HI-Q's website, and Alan's email earlier (before I started posting), that height and length are key. Even if I spend the money on a center loaded whip, I still may have reduced efficiency on 80m depending on how well I mount and insulate it.

I already have a relatively large radiator, if I make it a bit larger, and play some 'games' with it, I might spend less, and be better off. At least that is what I'm telling myself right now.

Now, how about experiences with capacitance either at the base or a hat?

Thanks all very much.

73
Tim
KA1YBS
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AA4PB
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« Reply #11 on: February 17, 2008, 04:13:12 PM »

I use an SG-237 and it tunes a 102-inch whip on 80M through 10M just fine. I'm sure its not as efficient on 80M as a good quality, full sized screwdriver but it makes contacts okay. Your mount and/or feed line may be the issue (too much capacitance to the vehicle). Check out a great insulator at http://www.geotool.com/antmount.htm. Also note in the picture the short feed wire between the tuner and the antenna and how it is well separated from the vehicle body.

Personally, I'd take an SG-237 over an AH-4 any day. The SG-237 covers 80M through 6M and its memory pre-sets are retained during power-off. The AH-4 does neither.
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K7AAT
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« Reply #12 on: February 19, 2008, 07:36:54 PM »


  Personally, I think you should have purchased the SGC 237 instead of the 239.  The 239 is not spec'd for 75M operation on less than a 40 foot whip.  The 237 is, on a 7 foot whip.

  Since it is unlikely you will be able to easily extend your whip to 40',  even for fixed station operation,  I guess you should be looking at other tuners.  If you only operate when stopped, though,  you might consider extending the length of the whip.  Even a few feet makes a world of difference to efficiency.


  Ed  K7AAT
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KE6AEE
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« Reply #13 on: February 19, 2008, 10:36:05 PM »

I've used a 102 inch whip with an AH-4 and an Icom 706 with world wide contacts when the bands are good.  The stainless steel whip is more dirable and rugged than a screw driver antenna.
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KA1YBS
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« Reply #14 on: February 19, 2008, 11:39:21 PM »

Hello group.

Thanks for all the suggestions, and experiences. I made a decision that some will disagree with Smiley

I purchased a used AH-4 coupler. For what it's worth, I take safety first, budget second, and actually learning fun stuff somewhere in between! Cash saved for future analytics and efficiency improvements.

Besides, a couple days ago I worked nearly 2 thousand miles using what could very well be a badly 'efficient' radiator (Don't ask me about the SWR hi), coupled with "0, 0, 0, 0 and 0 with a mean of 0", while modulating on about 9 watts PEP.

While driving... that has really boosted my interest in learning mobile HF! And it was a bunch of fun, too! It's peanuts, but I have to start somewhere.

...Now If only I could HEAR the other station better, HI!

Efficiency is going to take some time, work and experiment, and best of all, advice from this community.

I need to solve some RFI issues, maybe create a better ground plane, maybe learn how to tackle inductance and capacitance once again (It's been 10 years).

So here it goes... I'll be asking more questions.

Thanks in advance Smiley

73
Tim
KA1YBS
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