Help With Hi-Q Antenna

[AA8GK]

I own the Hi-Q 4/80 antenna (with 5 foot whip) and have had great success with it in the past, I mean GREAT DX. However, I've recently run into a problem with it: I'm no longer able to tune any band above 20 meters. Using the MFJ analyzer, I'm getting huge dips in SWR around 16 MHz, regardless of the antennas current setting. I'm not using any tuning network at the base (never needed one), and I've just replaced the coax and double checked ground connections from the coax. Any thoughts?

Thanks in advance,
Pete AA8GK

[KJ7BS]

Drop Charlie a note.  See what he has to say about your problem.

Mark Saunders, KJ7BS
Glendale, AZ

[K0BG]

I second the motion. When you say "dips" in SWR, are you speaking about it being too high? I suspect there is an internal problem, and if you're the original owner, it's warranted for as long as you own it.

By the way, grounding the base of the antenna has no effect on its performance. If it does (did), then something else is amiss.

Your statement about not needing a matching coil at the base leads me to conclude that the ground losses are rather high. Properly mounted, and with the vehicle properly bonded, the input impedance on 75 and 40 meters will be about about 20 and 25 ohms respectfully. That's a 2:1 SWR.

My own HiQ 5/80, which is body mounted (photos are on my web page), measures 18 and 23, and without a matching coil, I couldn't use it.

Alan, KØBG
www.k0bg.com

[K0BG]

I have an 8 foot whip on my 5/80, and 17 meters is as high as I can load it. I can, however, find a usable point (essentially 3 times the frequency) for 10, 12, and 15. The point is VERY sharp and not easy to hit dead on.

I haven't seen your install, so I can't comment any more than I have about the input impedance. One of the reasons you don't need input matching on some installation is simply this; the combined losses are enough to raise the input impedance very close to 50 ohms. Fact is, it isn't uncommon to measure some cheap antenna installations at over 60 ohms.

Here is something you can try. Connect an ohmmeter across the coil. You can loosen one of the coil mounting bolts to make sure you get a good connection. Power the antenna from one end to the other a couple of times. There should be very little change from one end to the other. The DC resistance will be very low; just an ohm or two. If it jumps erratically, you may indeed have a problem.

If you're still having problems even though the antenna is okay, send me an e-mail and we can discuss this off line with a little more detail.

Alan, KØBG
www.k0bg.com
k0bg@plateautel.net

[KG0SH]

Hi Pete,

I had the same problem with mine.  Drove me nuts.  I took it all apart, measured the coil with an inductance meter, spent hours with the MFJ analyzer, the works.  I could run the coil up and down as much as I wanted but could never get it to tune to anything more than about what you are seeing.  

What it turned out to be was that with my installation, I had a washer at the base that had slipped and shorted the base of the antenna to the mounting bracket I built.  This was sort of trying to "shunt feed" the thing, which didn't work very well.  Fixed the washer and all was well.  I have some photos of my installation on my web site at

http://home.comcast.net/~brucet622/wsb/html/view.cgi-home.html-.html  

Click on the photos link and look through the list.

I would check to see if the insulation washers are still doing their job or if something is shorted there.
I hope this helps.  Took me a long time to track this one down.  Good luck!

73,

Bruce, KG0SH
Golden, CO