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Author Topic: 500 Watt Hamsticks?  (Read 5151 times)
W9RRR
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« on: July 16, 2011, 07:22:02 AM »

I have a Jeep Grand Cherokee (hardtop SUV) with several 3/8-24 ball mounts on top.  I use a 3-way antenna switch to change easily between 20, 40, and 75 meters.   

I am using the MFJ hamsticks, but they are rated at 100 watts.  I want to add a small mobile amp (400 to 500 watts output) but don't want to mount a huge antenna like a 1500 watt screwdriver-type on the rooftop to handle the power.

Does anyone make a hamstick type antenna with bigger wire in the coil windings that can handle 500 watts?   I've checked the reviews here and every catalog I can find and it seems like nobody makes a high-power hamstick.  Or if they do, they keep a better secret than our military!  :-)

Thanks in advance for your comments!

-- Larry
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N5MOA
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« Reply #1 on: July 16, 2011, 08:13:41 AM »

hamstick.com, click on the catalog link.

On the last page, it says their HF mobile antennas have a pep rating of 600w.

You might give them a call.
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K0BG
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« Reply #2 on: July 16, 2011, 08:32:51 AM »

The truth is, if you install a decent quality screwdriver like the Scorpion, you'll gain more ERP than add an amp to a hamstick.
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W5DXP
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« Reply #3 on: July 16, 2011, 12:14:09 PM »

Normal hamsticks can be modified to handle 500 watts. Here's what I did.

http://www.w5dxp.com/bugstick.htm
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W8JX
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« Reply #4 on: July 16, 2011, 01:27:15 PM »

The truth is, if you install a decent quality screwdriver like the Scorpion, you'll gain more ERP than add an amp to a hamstick.

Pretty big stretch. Nothing wrong with a hamstick as I have used them for many years. Properly tuned they do real well. The only advantage a screwriver has over it is that it is multiband.
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K0BG
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« Reply #5 on: July 16, 2011, 03:07:19 PM »

Sorry, John, but it isn't a big stretch, and it has nothing to do with you using them for years. All one has to do, is read the results of the 3905 Group's antenna shootout. While they are not scientific, but nevertheless, the hamsticks are always at the bottom of the list.
« Last Edit: July 16, 2011, 03:14:56 PM by K0BG » Logged

W8JX
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« Reply #6 on: July 16, 2011, 08:20:07 PM »

Sorry, John, but it isn't a big stretch, and it has nothing to do with you using them for years. All one has to do, is read the results of the 3905 Group's antenna shootout. While they are not scientific, but nevertheless, the hamsticks are always at the bottom of the list.

I wonder how many take time to match them properly. I never used a tuner with mine and had SWR well under 1.5 to 1 most of the time too. ( I even tweaked it so it had it best match at highway speeds with antenna flexing back a bit) I still say it is a stretch on your ERP claim. All HF mobile antennas are basically negative gain antennas (except maybe 10 meters) because of their physical size. A screwdriver is not going to change this. What it does do is match antenna to radio better without a tuner. No magic here. I had my sticks on a quick disconnect on a bumper mount and ran 40 and  20 mostly. I even worked VK's a few times going to work in early morning on 40 with sticks with a decent signal for a mobile. I doubt a screwdriver would have done any better. Again I did tune mine and if you do not then a screwdriver will work better than a mistuned stick.
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K0BG
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« Reply #7 on: July 17, 2011, 07:10:29 AM »

John, you comment about a low SWR sort of tells the story, if indeed you can get the SWR lower without matching. Fact is, I've never seen a hamstick that needed matching. Most folks just tune them a bit off the high side, so the SWR appears lower, but the antenna has a significant amount of reactance. The radio isn't all that happy, but the SWR bridge is.

And just for the record, even on 6 meters, you have essentially negative gain. The major issue here is ground loss, and if you use a stainless steel whip you have to subtract another dB or so.

Lastly, lots of folks use hamsticks, for a variety of reasons despite their inherent losses, and are happy. But please, don't justify them by stating how low the SWR is, or how many DX stations you've worked with one.
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W5DXP
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« Reply #8 on: July 17, 2011, 10:18:46 AM »

Nothing wrong with a hamstick as I have used them for many years. Properly tuned they do real well. The only advantage a screwdriver has over it is that it is multiband.

On 75m, the hamstick has been measured to be 10 dB down from a comparable screwdriver and 12 dB down from a screwdriver with top hat. The 75m hamstick loading coil is very low Q, i.e. inefficient. The screwdriver loading coil is relatively high Q. A good screwdriver design might be ~10% efficient on 75m while a hamstick may be below 1% efficiency. Try transmitting a continuous 100w signal for 15 seconds and then grabbing the top of a 75m hamstick loading coil but be careful - it's like grabbing a 100 watt light bulb. 75m hamstick users must really like QRP operation. Smiley

http://www.w5dxp.com/shootout.htm

The ARRL Antenna Book has a comparison of loading coils with Q's of 50 vs 300. The Q=50 75m coil has a loading coil resistance of 72 while the Q=300 loading coil has a loading coil resistance of 12. That 6/1 ratio of Q's gives the high-Q antenna a considerable edge in efficiency.

However, on 20m-10m a hamstick is reasonably efficient and I use one for 17m operation.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WB6BYU
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« Reply #9 on: July 17, 2011, 05:03:33 PM »

Quote from: W5DXP
...A good screwdriver design might be ~10% efficient on 75m while a hamstick may be below 1% efficiency. Try transmitting a continuous 100w signal for 15 seconds and then grabbing the top of a 75m hamstick loading coil but be careful - it's like grabbing a 100 watt light bulb...


And that is the problem with designing the antenna for 500 watts:  at 1% efficiency and high coil losses,
the antenna has to dissipate most of the RF as heat.   How can you improve the power rating?

(1) make the antenna out of high temperature materials , fatter wire, and good heat sinking to dissipate
500W without overheating.  This is expensive.

(2) use a loading coil for a higher frequency band with a longer whip and/or top hat.  This is a good
approach, but has limited range for improvement and will be much longer than the original.  (You
can also add an extension at the base of the antenna, such as a Hustler bottom section, or even
the bottom section of a hamstick for a higher band.)

(3) reduce the loading coil losses by increasing the Q.  The best way to do this is to increase the
diameter of the coil and the spacing between turns.  (There simply isn't enough room on a 1/2" x 4'
fiberglass shaft to wind an 80m loading coil with sufficient turn spacing and big enough wire.)  There
are lots of mobile antennas that take this latter approach, such as the Texas Bugcatchers and
many homebrew antennas.  Putting the coil near the middle of the antenna, rather than distributed
from the bottom to the middle, helps, too.  But then, it is no longer a Hamstick, and the fatter
antenna will have more wind drag, etc.


Quote
However, on 20m-10m a hamstick is reasonably efficient and I use one for 17m operation.

And that is a point that tends to get lost in such discussions:  a Hamstick-type antenna is
often very inefficient on 80m, better on 40m, and reasonably good on 20m and up.  Detractors
tend to focus on the 80m performance, proponents on the higher bands.  They really are
not comparable.
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W8JX
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« Reply #10 on: July 18, 2011, 07:52:03 AM »

I would never promote a Hamstick to 80 meters or even a screw driver as they are both basically dummy loads on 80. It takes a specialty antenna designed for 80 to give reasonable performance on 80. At 40 and above hamsticks work pretty good if you take time to match them properly (and that does not mean using a tuner rather than tuning antenna)
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W8JX
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« Reply #11 on: July 18, 2011, 08:01:04 AM »

John, you comment about a low SWR sort of tells the story, if indeed you can get the SWR lower without matching. Fact is, I've never seen a hamstick that needed matching. Most folks just tune them a bit off the high side, so the SWR appears lower, but the antenna has a significant amount of reactance. The radio isn't all that happy, but the SWR bridge is.

I could tell when I was out of the sweet spot on my sticks as output power would fall off noticeably for SWR clampdown. On 40 I had 50 to 60KC or so to use with good SWR. On 20 it was much broader. My poor mans SWR bridge back then on the road was radio output power. Overall I was pretty pleased with how they worked. I used 40, 20, 17 and 15. Had sticks 12, 10 and 80 too but rarely used them. (I think I had 2 or 3 contacts on 80 the one time I tried it)
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W5DXP
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« Reply #12 on: July 18, 2011, 08:54:35 AM »

It takes a specialty antenna designed for 80 to give reasonable performance on 80.

I used to think the same thing until a screwdriver antenna tied with my junkbox specialty antenna and with the top rated bugcatcher antenna at one of the CA shootouts. The picture at the top of this web page shows how to turn a screwdriver antenna into a top 80m performer with an RV bottom section plus top hat.

http://www.w5dxp.com/shootout.htm
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K8KAS
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« Reply #13 on: July 19, 2011, 06:21:30 AM »

88JK, please, please SWR is not the end of the world, the antenna's efficiency is what mobile antennas are all about. The BIG screwdriver antennas on 75 meter's KILL something like the Hamstick by 10 db or better. I worked at two commercial antenna testing ranges and in my spare time played with Mobil antennas, on 75 meters, 10 db was normal between a Hamstick and my Tarheal 200 with a 6 foot top whip and a small top hat, on 40 meters 3 or 4 db in favor of the Tarheal and on the upper bands 20/17/15 and 10 meters it was a db or so between them. PS, I like Hamsticks BUT there are better antennas for sure.

FYI --10 db on 75 meters is day and night, you can really enjoy 75 meter Mobil with a screwdrive/bugcatcher, etc BIG antenna.

FYI if you have ever been to a Mobil Antenna Shootout you can see the efforts and the antenna knowledge that some of the Ham's have in Mobil antenna's, they are not a bunch of newbies,  for the most part they understand what it takes to make Mobil antenna's perform.. IMHO  73 Denny K8KAS
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G8YMW
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« Reply #14 on: July 19, 2011, 02:02:29 PM »

One of the lessons to be learned here is SWR does not equal resonance.
To quote G3YXM
"A good big mobile whip on resonance on the LF bands will present an impedance of about 20 Ohms to the rig, it won't like this! Any 160/80/40m whip that gives a perfect match on resonance is LOSSY, don't believe the hype! To feed your 20 Ohm super-whip you can either use a transformer, available from retailers or home made, or use capacitive matching as I do"

20 Ohms (ish) is about 2.5:1 SWR as  is 125 Ohms (Watch the radio "fold back")
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73 details Tony
Sent by WW2 Royal Navy signal lamp
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