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HF Vertical Multi-band

binrat

binrat

WDX Club Coordinator
Staff member
Nov 5, 2008
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The Great White north
Is anyone using one?

I'm going to have to use one at the new QTH. I was looking around and the DX Engineering MBVA-1UP THUNDERBOLT looks pretty promising.
Thoughts, comments please.
 

It's just 43 feet of aluminum tubing with a base. You still need a tuner and the best place for that tuner is at the base of the antenna so a remote tuner is best. Add in that as well as a radial plate and a tilt over base and you could have a multiband trapped vertical and not worry about tuning except for maybe 40m and 80m. If I already had a remote tuner (and I do) perhaps I would use it but not if I had to buy one extra. Just my opinion mind you.

BTW I never could understand the reasoning behind a length of 43 feet. It's not resonant anywhere. Maybe that is the idea. Beats me.
 
Captain Kilowatt said:
It's just 43 feet of aluminum tubing with a base. You still need a tuner and the best place for that tuner is at the base of the antenna so a remote tuner is best. Add in that as well as a radial plate and a tilt over base and you could have a multiband trapped vertical and not worry about tuning except for maybe 40m and 80m. If I already had a remote tuner (and I do) perhaps I would use it but not if I had to buy one extra. Just my opinion mind you.

BTW I never could understand the reasoning behind a length of 43 feet. It's not resonant anywhere. Maybe that is the idea. Beats me.
Click to expand...
Thanks Captain.
I don't plan to do an amp at this time so a remote 200 w tuner could be in my budget. I was thinking 43' is a weird height. At that diameter of tubing it would be easy to push it up to 1/4 wave for 80 Metres, or shorten it for 1/4 for 40 as well. I have about an area of 45' x 65' of a back yard.
 
I was thinking the same thing about using it a a regular 1/4 wave on 20 and 40m. No tuner required but it would require manual adjustment every time you wanted to change bands. Going to a 1/4 wave on 80m would require an additional 20 feet so you would want something strong yet low wind load. I don't know.....for $400+ I would have to think long and hard about some wire antenna options or a home brew vertical using aluminum pipe and/or PVC or ABS pipe first. Again just my opinion.
 
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I think MR. FX has a thread about a multi band vertical, built out of wire.
 
Captain Kilowatt said:
It's just 43 feet of aluminum tubing...BTW I never could understand the reasoning behind a length of 43 feet. It's not resonant anywhere. Maybe that is the idea. Beats me.
Click to expand...

we have an informal group that ragchews in the evening. one of our regulars uses a 43 foot (MFJ) antenna.

he has one of the better signals. ..... BTW, this is on 60 meters;)

$400?........... a little steep for my blood
 
Captain Kilowatt said:
BTW I never could understand the reasoning behind a length of 43 feet. It's not resonant anywhere. Maybe that is the idea. Beats me.
Click to expand...

I seem to remember reading something on long wire antennas that the best length was one that was not near an electrical half wavelength multiple on any band you intended to use it on. This allowed the tuner a higher chance to be able to tune the antenna on all of those bands... I'll have to see if I can find that data again. If it applied to long wire antennas I assume it would apply to these antennas as well.


The DB

EDIT: Here are some links for reference...
link1
link2
 
Last edited:
The DB said:
I seem to remember reading something on long wire antennas that the best length was one that was not near an electrical half wavelength multiple on any band you intended to use it on. This allowed the tuner a higher chance to be able to tune the antenna on all of those bands... I'll have to see if I can find that data again. If it applied to long wire antennas I assume it would apply to these antennas as well.


The DB

EDIT: Here are some links for reference...
link1
link2
Click to expand...



Entirely possible that was the reason for 43 feet. Most automatic tuners cannot handle the impedance and voltages associated with feeding an end fed half wave antenna.
 
Hmm. The way I read the information was that 43 feet was one of those lengths to avoid. Did I goof?
- 'Doc
 
Thought 1:
48 feet shows up for 10 meters and is based on the width of a wire. What happens to that electrical length when you factor in the width of a much thicker aluminum vertical element?

Thought 2:
If there are buried radials of any length that will help the tuning of these types of antennas as the feedpoint impedance will drop as compared to an end fed variant. This would also change the lengths used above as the antenna is now the electrical length of the vertical plus the electrical length of the radials that were added. I mention this because the MFJ version of this length of antenna in their catalog shows what appears to be attached radials to the mount. I have also found other pictures around the web that show the same thing from these antennas from other manufacturers.


The DB
 
They recommend
"Of course, another key to performance is a good ground radial system. We recommend 32 radials that are 65 ft. long. Fewer radials will work, but with diminished results."
My site does not work for the 65' so I was thinking 40 x 32' radials.
 

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