help on an antenna DB222

[wp4mxb]

i have this antenna db222 but need help to tune it to ham band can anyone help me !!!!!

[440roadrunner]

Do some "Googleing", or at least the engine of your choice. There was at least one article on the 'net about welding (?) some nuts/bolts on the ends of the loops to retune them. If I can find it, I'll post back. I do NOT know, however, what this'll do to the phasing harness.


Well, I found the saved webpage on my computer, but it's either not online, or has been moved. Get ahold of KC4FWC if you can, he is evidently the original author.

Repeater builder has a project on a "look alike" 4 bay loop dipole that's been around for years.

http://www.repeater-builder.com/antenna/440fdipl.pdf


http://www.repeater-builder.com/rbtip/e ... ipole.html

[tvsjr]

What band is it currently on? If it's a standard 150-160 split, you might try sweeping the antenna with a Sitemaster or spec-an/tracking generator/return loss bridge, or at minimum cabling your radio up and looking at reflected power with a wattmeter. You may find the antenna is just fine as-is.

One of my repeaters (RACES primary for the county, 146.980 output) is currently operating on a 150-160 split DB264. I suppose I could've replaced it, but this antenna was already mounted at 370' with like-new 1-1/4" hardline run to it and was offered to me in-place. I'm seeing <1.1:1 VSWR, which is plenty acceptable to me...

[Birken Vogt]

i have this antenna db222 but need help to tune it to ham band can anyone help me !!!!!

Some hams around here cut all the elements about midpoint between the cross bar and the end, welded in some aluminum rods to lengthen them, built a new cable harness, and are using that duplexed on a repeater. Was a DB224 also, what a lot of work that must have been but it works excellent

Birken

[kf4sqb]

I have also heard of people drilling a hole in the bottom of the 'loop' of the antenna, and installing a 'rod', pointing straight down, to adjust the tuning. I have never tried this myself, and have no idea how well it works. I would expect that it would distort the radiation pattern at least a little.

[k4iii]

...

[Jim202]

Over the great span of the years, there has been much published on modifications to this type of antenna.
Most of the mods also include changes to the phase harness. Be careful here as the different sections
have different type of coax used. Some of the phase harness sections are made from 32 Ohm coax.

Going down in frequency is a major problem as your lengths will need to be longer and not shorter.

Bad issue here is when Andrew took over the DB series of antennas, they cut out the ability to obtain
replacement harnesses. Guess the big wigs figured out that if you need a new set of cables and they
are no longer available, you will be forced into a new antenna. Great point of view, it didn't go over
very big with all the end users. Still not sure where that issue will end up and play out. If it was me,
I would kiss Andrew off and go to another brand of antenna. Like I said, not sure where this will play
out on the no replacement harnesses available.

Good luck on your mods.

Jim

[mike m]

I did what you want to do with a DB-222 which was centered around 158 MHz.

Talking with Fred at DB products he didn't think that the harness needed any modifications, so I just increased the folded dipole element lengths by ~3/4 inch on each end, 1.5 inches total.

As for the element mods, here is what I did:

Around 2 inches back from the curved end of the folded dipoles I cut the elements on each side, top and bottom of course, with a hacksaw and then I used some thick walled aluminum tubing with a Inside Diameter that was the same as the original elements Outside Diameter.

These aluminum extensions were 2 inches long on each side, top and bottom of the folded dipole loops, 4 aluminum extensions per folded dipole element.

The extensions increased the length around 3/4 to an inch on each side of the folded dipole elements.

I then used penetrox and rivets to attach the extensions over the original tubing and sealed the interface with RTV.

When finished my VSWR was 1.1:1 at 146 MHz.

I haven't had any problems with the rivets pulling out after 2 years of operation.

Looking back on things if you can have the extensions Aluminum welded that would be a better option but my method and merchandise was all done from one Home depot trip.

You can also use solid rod that fits inside the original elements as opposed to tubing that fits over the original tubing and weld the extensions for a nice rugged assembly.

Mike

[Jim202]

The issue with not looking at the phasing harness is that it effects the antenna radiation pattern.

You can do what you want, but just thought you should be informed that using the original harness
will produce a non standard pattern from the tower when the operating frequency is pushed down
that far to the ham band. Been there and tried that before.

Tried all sort of things like moving the antenna further away from the tower, closer to the tower,
didn't change the problems. Ended up installing a new harness cut for the operating frequency
and it all started playing like it should.

Jim