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Author Topic: 20M Hamstick On Multiple Bands  (Read 2240 times)
K0BG
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« Reply #15 on: May 14, 2006, 07:40:56 PM »

Bill, while it appears on the surface that what you say is true, there is a lot more to it than a simple resistive mismatch causing an SWR of 6:1 or even 10:1. In the case of an 8 foot whip on 40 meters, the input SWR is over 1,000:1. You read that right; over one thousand to one! Actually, it is much more, than this. It's been a long time since I calculated it, but if memory serves, it's almost 2,400:1.

That's not all. With just 100 watts input, the RF voltage present exceeds the rating of even 1/2 inch hard line.

Again, this is a much misunderstood concept that is a lot more than just a resistive load mismatch. The ARRL Antenna handbook covers this quite well in chapter 24, as doe the ARRL Communications Handbook in several different sections.
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K3AN
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« Reply #16 on: May 16, 2006, 01:15:07 PM »

A thousand to one? Wow! I imagine that if one were to extrapolate the Handbook's SWR loss curves out to that number, the cable loss would indeed approach 100%.

But whatever angle on the Smith Chart SWR circle the load happens to be at (purely resistive, capacitive angle, or inductive angle), the SWR loss in the cable will be the same. The transmission line chapter doesn't identify any exceptions to the use of the chart.
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AA4PB
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« Reply #17 on: May 17, 2006, 08:11:37 AM »

What we are trying to tell you is that the loss in the coax due to high SWR is NOT the issue. A three foot piece of coax will not have a great deal of loss on 80M regardless of the SWR. It's lumped capacitance however will surely make an 8-foot whip (read very high impedance) antenna a very inefficient system.
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VE1IDX
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« Reply #18 on: May 18, 2006, 05:05:06 PM »

K0BG,I never said it was a great antenna only that it did present a decent match and allowed me to make several contacts on 6m without changing antennas.I agree that a low SWR has NOTHING to do with the efficiency of an antenna.As many folks have stated,a dummy load has a great SWR but is not much good for Dx'ing with. Smiley  I would consider using a loaded  antenna like a Hamstick on a band it was never intended to ONLY if the SWR was decent.I would not want to run one with a tuner to make my rig happy because God only knows what the reactance voltages will do to the loading coil and insulation.   Sad
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WI7B
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« Reply #19 on: May 19, 2006, 11:14:41 AM »


OMs,

I have learned something more about the capacitive reactance in coax and HF mobile whip antennae in reading this forum topic.  I'd just like to respond to the original question back a page or two.

I was fortunate enough to purchase the entire Iron Horse series of mini-HF (spirally-wound) antennae before they ended production.  These are the equalivalent of, not a "wet noodle", but a "half wet noodle" radiator.  Despite their poor efficiencies, I easily enjoy world-wide QSOs with the 20m mini-HF (about 25" tall) mag-mounted to the roof of the SUV with 100W input.  I have tuned the stinger to match the middle of the 20m band to my TS-480SAT w/o auto-tuning.  I then insert a small Versa tuner and tune it until low SWR is achieved, again.  In this fashion, I am able to then use the TS-480SAT auto-tuner to tune the entire 20m band while mobile w/o further manual adjustment to the Versa tuner or stinger.  Of course, all this is at resonance.

I also work 60m.  I did this by replacing the stinger in the 75m mini-HF if a "cut-down" version. Inserting into the coil, I folow a similar procedure in tuning up the rig. It all works fine throughout the five channels on 60m we are allocated.  The efficiency is horrid, but the antenna appears resonant, and radiates.

73,

---* Ken
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KB9BVN
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Posts: 116




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« Reply #20 on: May 27, 2006, 02:37:42 PM »

I bought Anttron Hamwhips, used, for 10, 20, 30, and 40m a few weeks ago.  I got to play with them to some length over the last couple of weeks and I never knew mobile ops could be so much fun.

I used my MFJ-259B to adjust the whips for best SWR in the middle of each band. On 20m last weekend I workd WA and OR from central Indiana with my 4w KX1 and the 20m Hamwhip on my 2004 Taurus.  Today I tried the 30m Hamwhip and worked a op in MI about 300 miles from here with 4w and the KX1 in my Taurus.

I have the 40m tuned up but I have not tried a QSO with it yet.  For some reason the SWR is 2:1 no matter what I do with the 40m whip...the 20m and 30m are all tuned to 1.1:1 or 1.3:1 for their respective bands.

Do you think I might need to add a capacitor?
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KB9BVN
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Posts: 116




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« Reply #21 on: May 27, 2006, 02:38:15 PM »

I bought Anttron Hamwhips, used, for 10, 20, 30, and 40m a few weeks ago.  I got to play with them to some length over the last couple of weeks and I never knew mobile ops could be so much fun.

I used my MFJ-259B to adjust the whips for best SWR in the middle of each band. On 20m last weekend I workd WA and OR from central Indiana with my 4w KX1 and the 20m Hamwhip on my 2004 Taurus.  Today I tried the 30m Hamwhip and worked a op in MI about 300 miles from here with 4w and the KX1 in my Taurus.

I have the 40m tuned up but I have not tried a QSO with it yet.  For some reason the SWR is 2:1 no matter what I do with the 40m whip...the 20m and 30m are all tuned to 1.1:1 or 1.3:1 for their respective bands.

Do you think I might need to add a capacitor?
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KB9BVN
Member

Posts: 116




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« Reply #22 on: May 27, 2006, 02:38:25 PM »

I bought Anttron Hamwhips, used, for 10, 20, 30, and 40m a few weeks ago.  I got to play with them to some length over the last couple of weeks and I never knew mobile ops could be so much fun.

I used my MFJ-259B to adjust the whips for best SWR in the middle of each band. On 20m last weekend I workd WA and OR from central Indiana with my 4w KX1 and the 20m Hamwhip on my 2004 Taurus.  Today I tried the 30m Hamwhip and worked a op in MI about 300 miles from here with 4w and the KX1 in my Taurus.

I have the 40m tuned up but I have not tried a QSO with it yet.  For some reason the SWR is 2:1 no matter what I do with the 40m whip...the 20m and 30m are all tuned to 1.1:1 or 1.3:1 for their respective bands.

Do you think I might need to add a capacitor?
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KB9BVN
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Posts: 116




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« Reply #23 on: May 27, 2006, 02:39:43 PM »

Hmmmm...I wonder why that happened...I swaer I only hit the save button once....
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