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Author Topic: Hustler Mobile HF SWR  (Read 590 times)
WS7X
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Posts: 25




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« on: August 21, 2007, 03:07:40 PM »

I've been using the hustler resonators for mobile HF for many years with good results on at least 3  vehicles I've owned. Recently, I got a new truck and transferred the hustler, (I use the 4' mast) to a 2006 Dodge Ram 3500 diesel pickup. And although my installation works, I've not been able to get as good an SWR match as with previoius installations.  I'm guessing that the location I've chosen is the main culprit of the poor SWR, (right behind the cab) and I'd probably get better results if I moved the antenna to the rear of the bed.  But that's not an option because I pull a goosneck trailer and so the back of the bed is out.  

I'm looking for a way to improve the SWRs for 20 40 and 75 meters in particular. Anyone know of way to improve the SWR of the hustlers?  
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K0BG
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« Reply #1 on: August 21, 2007, 04:13:33 PM »

The first thing you need to do is find out what the input impedance is. An SWR bridge won't tell you that. For example, a 2:1 SWR could mean the input is either 25 or 100 ohms.

Due in part to the antenna being close to the body, there is additional stray capacitance between the mast and the body. This increases ground losses, and raises the input impedance.

What you need is an MFJ 259b antenna analyzer. If you can't afford one, try to borrow one from a friend.

Alan, KØBG
www.k0bg.com
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WS7X
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« Reply #2 on: August 21, 2007, 10:36:34 PM »

K0BG Thanks for your reply.  Ok it's easy enough to get my hands on a 259B and measure the impedance.   So how would I go about getting the impedance close to 50 ohms.  I"m assuming that's where you're going.

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K0BG
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« Reply #3 on: August 22, 2007, 06:01:05 AM »

Most of what you need to know is on my web site under Matching.

A Hamstick, and similar, small, spirally wound, antennas are rather lossy. This pushes the input impedance up. Usually the mismatch is small. However, when you mount one close to the body of the vehicle, the stray capacitance pushes the input even higher. This is especially so if the main coil is close to the body.

Once you determine what the input is, then the fix is easy. The aforementioned article will tell you how.


Alan, KØBG
www.k0bg.com
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WS7X
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« Reply #4 on: August 22, 2007, 10:09:54 AM »

K0BG,
I appreciate your reply.  But can you be more specific on the "how" to accomplish the "easy" match.  I've looked at your website and there is a great deal of information there.  What it lacks however are specifics on how to accomplish the impedance matching.
 For example looking at the shunt feed picture under Impedance Matching.  How can I find the correct coil size for my particular installation? I can make a coil that will match each band, but how can I make one that will match 3 bands. Because of my installation I cant easily change coil taps for every band.  Instead I need to make one coil that will give me an acceptable match for 3 bands.  I'd even settle for just 40 and 80 meters.  Is there a way to use the MFJ 259b to find a good compromise coil?

Again specifics please.  For example, you could have just said try a shunt feed coil of 9 turns #14 gauge at the start.

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AA4PB
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« Reply #5 on: August 22, 2007, 11:41:46 AM »

I had a Hustler installation that gave me around a 2:1 SWR on all of the bands. Checking I found the impedance was close to 25 ohms. I used a 2:1 UNUN to give me a good impedance match on all bands.

The problem with many other matching methods (capacitor or inductor) is that the matching needs to be changed when you change bands.
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K1DRW
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Posts: 15




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« Reply #6 on: August 22, 2007, 03:56:40 PM »

Lakeview (the Hamstick people) makes a matching coil that
works great on 40m and 75m Hustler resonators.

It is called the WD4BUM inductimatch.  It is an inductor across the feedpoint. Physically it is a 3 inch air wound coil that mounts at the base of the hamstick with a ring terminal and slightly overlaps the lower part of the antenna.

There is a short lead with a an aligator clip that is used to tap the coil to ground,
effectively putting inductance across the feedpoint.

See it here: http://www.hamstick.com/im1.htm
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