DB-304 Wiring Harness

nukesnooper · May 19, 2015

I have an aging - but still in great structural shape - DB-304 8 bay VHF antenna with a bad wiring harness. I'm only showing continuity between the two next to the bottom elements. And, yes; I know it's DC grounded and removed the center conductors from each element before testing continuity to the center conductor of the N connector. Likely a lightning hit at some point in its life.

Any suggestions regarding how to replace the phasing harness since they are no longer available? I found a company in Canada who were willing to rebuild one for $350.00 plus me shipping the old one up there, as well as return shipping. The cost doesn't pass the sanity test. I know that it's relatively inexpensive compared to the antenna, but it's not something I can't come anywhere near affording.

And, I'm no genius with respect to using different impedances of coax and matching them in weatherproof splits.

Any help will be greatly appreciated!

nukesnooper · May 19, 2015

Edited: Forgot to add that I have the original CAD / Blueprints with specs of the harness from the manufacturer.

prcguy · May 19, 2015

The harness on a DB Products dipole array is a bit complex but most companies simply use critical lengths of 75 ohm coax to make a power divider. If you look for the pdf file in the link, at the end it has dimensions for a simple power divider harness to feed a 4-bay dipole array. You can use just two "Cable A" and one "Cable B" lengths to make one for a 2-bay array.

The coax used was Belden 1505A, which is similar to RG-59 and its best to tune the harness with an antenna analyzer to the center of the frequency range you need. The harness in the pdf worked well over 142 to 162Mhz and you can use PL-259 connectors and a Tee adapter or F connectors and and F Tee adapter, etc. If you copy the pdf dimensions just make sure you use Belden 1505A and the overall cable length with connectors and adapters is the same as the pdf.
prcguy

http://forums.radioreference.com/build-your-own-antenna/109144-4-bay-vhf-dipole-array-project.html

nukesnooper · May 20, 2015

Nice article. Well done. Ingenious!

I have the CAD / blueprint drawings from DB Products that show the various coax lengths and impedances of each run. They even show the internal parts inside the splitters and how to solder and assemble them. I'd like to try to stick to as close to stock as I can. Reason being; I'm a bigger fan of (well done) soldering the connections / junctions than taking the chance of loss or noise using "T" connectors. And, there would be a LOT of them with that many elements. My biggest concern with either soldering or "T" connectors is weatherproofing them. I have Andrew coax tar wrap, and other options, if need be.

I'd also likely use "N" connectors and "T's" as opposed to PL-259, and definitely not "F". The stock diagrams show various combinations of coax impedances - anywhere from 42 to 58 ohms, depending on the location on the harness. Where in the world would I get just a couple of feet of 42 ohm coax??? 58 ohm, for that matter. It's a really strange beast. And huge! 33' from top to bottom of the center mast.

I want to do it top notch because I'll be using it on a 2m (147.080 / 147.680) MSF5000 repeater pushing 150 watts. Not just for casual listening or chit chat.

Thanks for the input. I thought I had the blueprints on my thumb drive, but apparently, I've archived them on my home server, having given up on the project about a year ago. Just can't bear to throw away such a nice antenna. But; can't afford $350.00+ for a wiring harness. Although; the Canadian firm (JAG) would rebuild the entire antenna - with elements cut to my specific frequency for $850.00. I know that's incredibly cheap, but WAY out of my budget for an antenna that's not generating income. Particularly if you consider the freight back and forth.(!) UPS quoted me $143.00 - just for the harness, since it was going to Canada! Fed-Ex quoted me a much more reasonable $48.00. I can't imagine the cost to ship the entire antenna!

I'll post the drawings as soon as I find them for you to take a look at. I may very well go your route. I just want to be sure that I have a good match before I hoist this beast to the top of a 50' Rohn 25 tower.

Thanks again!

prcguy · May 20, 2015

F connectors are much better than most people think. You could use RG-11 coax, which is about the same dia as the stock harness with T&B Snap-N-Seal compression connectors and type F Tee adapters. One popular high performance antenna company (M2) uses F connectors and RG-6 on their T match for VHF and UHF Yagi's and those antennas are rated for at least 1,000w.

I purchased 2 DB Products 4-bay VHF arrays, one Maxrad VHF 4-bay, 2 Cushcraft VHF 4-bays and 1 Radio Frequency Systems VHF 4-bay arrays on Ebay, all new and with harnesses but no masts and the most I paid was $75. Point here is a complete surplus antenna will cost less than paying for a new factory harness.
prcguy

nukesnooper said:
Nice article. Well done. Ingenious!

I have the CAD / blueprint drawings from DB Products that show the various coax lengths and impedances of each run. They even show the internal parts inside the splitters and how to solder and assemble them. I'd like to try to stick to as close to stock as I can. Reason being; I'm a bigger fan of (well done) soldering the connections / junctions than taking the chance of loss or noise using "T" connectors. And, there would be a LOT of them with that many elements. My biggest concern with either soldering or "T" connectors is weatherproofing them. I have Andrew coax tar wrap, and other options, if need be.

I'd also likely use "N" connectors and "T's" as opposed to PL-259, and definitely not "F". The stock diagrams show various combinations of coax impedances - anywhere from 42 to 58 ohms, depending on the location on the harness. Where in the world would I get just a couple of feet of 42 ohm coax??? 58 ohm, for that matter. It's a really strange beast. And huge! 33' from top to bottom of the center mast.

I want to do it top notch because I'll be using it on a 2m (147.080 / 147.680) MSF5000 repeater pushing 150 watts. Not just for casual listening or chit chat.

Thanks for the input. I thought I had the blueprints on my thumb drive, but apparently, I've archived them on my home server, having given up on the project about a year ago. Just can't bear to throw away such a nice antenna. But; can't afford $350.00+ for a wiring harness. Although; the Canadian firm (JAG) would rebuild the entire antenna - with elements cut to my specific frequency for $850.00. I know that's incredibly cheap, but WAY out of my budget for an antenna that's not generating income. Particularly if you consider the freight back and forth.(!) UPS quoted me $143.00 - just for the harness, since it was going to Canada! Fed-Ex quoted me a much more reasonable $48.00. I can't imagine the cost to ship the entire antenna!

I'll post the drawings as soon as I find them for you to take a look at. I may very well go your route. I just want to be sure that I have a good match before I hoist this beast to the top of a 50' Rohn 25 tower.

Thanks again!

nukesnooper · May 20, 2015

I guess I can't post pdf files. I found my assembly sheet for the DB304, but can't post it for you to take a look at it.

I'll research this a little longer and see if I can figure out what cable lengths to use in making this octopus.

Thanks for all of the suggestions and help.

mancow · May 20, 2015

nukesnooper said:
I guess I can't post pdf files. I found my assembly sheet for the DB304, but can't post it for you to take a look at it.

I'll research this a little longer and see if I can figure out what cable lengths to use in making this octopus.

Thanks for all of the suggestions and help.

I can host it if you can email it. If you want to send a private message with an email address I will reply and we can go from there?

talkpair · May 20, 2015

http://www.repeater-builder.com/antenna/db/pdfs/db-304.pdf

This might be what you're looking for.

No dimensions for the 2m bandsplit though.

nukesnooper · May 21, 2015

Thanks. It is the one. I'm the one who donated it. I'm Jim.

talkpair · May 23, 2015

I'm kind of curious about what bandsplit this antenna is in.

Did you ever use it on 2 meters and how did it perform?

If you only have continuity between a couple points in the entire harness, I'd say there's nothing there to rebuild.

Do you think some of the 35 ohm and 42 ohm cables can be reused?
These are sections C and D on the print.

nukesnooper · May 26, 2015

I've never used the antenna. It was one that was decommissioned from a tower that had been abandoned. The manufacturer decal is no longer legible, but I can only make out 15xxxx on the band split area. I don't recall the exact dimensions of the elements, but I can re-measure them. If I remember correctly, the length of the elements indicated a center frequency of around 155.000MHz with a +/- 10MHz operating range, which would still put it in my target range of 147.080MHz.

From the center lead of the "N" connector that ties into the duplexer, I can only read continuity between the two second from the bottom leads on the harness. No continuity between any of the others - even from element to element. No; given the age (in appearance) of the harness, I doubt that the original harness could be rebuilt. There are hard plastic injection molded junctions that join the individual splits. I don't think that they would be too easy to remove without further damaging the harness. I suppose it's worth a shot just to see what the "connections" look like. My hunch is that they were smoked by a lightning strike - although there is no evidence of thermal damage. But; I can't imagine that many "opens" by any other means.

I can take some photos and provide measurements if you think that might help get me into the ballpark. I just don't have the ability to post photos on here, that I know of.

nukesnooper · May 26, 2015

The physical dimensions are as follows:

Overall mast length= 21.5"
OD element lengths (x8)= 2' 3/4"
Element diameter=3/8"

The bottom 4 elements are spaced 28" apart. Same with the uppers. But; the spacing between the top element on the bottom and the bottom of the bottom element of the top 4 elements is 24"?

I hope this helps someone determine a realistic operating frequency. If you need more information, please post.

Thanks!

talkpair · May 26, 2015

OD element lengths (x8)= 2' 3/4"

That measurement doesn't look right.

If you meant 36.75" instead of 24.75", you're probably in luck.

Looking over the DB220, DB222 and DB224 element document, everything from 131 up to 174 MHz pretty much use the formula below for the elements.

For the harness, measure from the tip of the feedline connector to the center of the first 3-way splice, then compare it to Dimension D of your DB-304 PDF file.

talkpair · May 26, 2015

This formula is less confusing than the one previously posted.

nukesnooper · May 27, 2015

I'm positive that they aren't 3'+ each. I'll re-measure at lunch to confirm. I also have a DB224, but the elements are different lengths (not by much), but I've used it previously with great success on 2m. I'll re-measure in a few.

prcguy · May 27, 2015

If the elements are about 24" long overall it could be a commercial 220MHz version.
prcguy

nukesnooper · May 27, 2015

My bad. The elements are 32.5" tip to tip on all 8 elements. The feed line is approximately 9' from input to the first 3 way split.

I tried to do the math, but I'm no genius and didn't get anywhere in the ballpark as far as number.

The elements on the DB224 are 34 inches tip to tip with the feed line also being around the 9' range.

I don't see a Dim D on the chart. Just A-C.

talkpair · May 27, 2015

My bad. The elements are 32.5" tip to tip on all 8 elements.

This works out to 163.425 mHz

The feed line is approximately 9' from input to the first 3 way split.

9' = 108"

Dimension D is on the chart at the bottom of page 2 of the PDF:

114".......150-160 mHz Range
108".......155-165 mHz Range
101-7/8"...164-174 Mhz Range

....but I can only make out 15xxxx on the band split area.

That eliminates the 164-174 range.

It looks to me like the antenna you have covers the 155-165 range.

The chart I have for the DB224E (143-150 mHz) shows it's element 37" from top to bottom. Your elements are 4.5" short.

Maybe others will have some ideas, but the chances for failure seems pretty high to me.

nukesnooper · May 28, 2015

So, aside from me shipping the wiring harness, elements, and blueprints to JAG and having them build a new harness and elements for $850.00, it looks like I have a large piece of aluminum scrap. Well; that's a bummer.

Maybe I can cut it into sections and sell it to a metal recycler. It weighs about 35lbs. It stinks to destroy such a good prospect, but no sense in letting it gather more dust and space in my back yard.

At least I've used the DB224 on my MSF5000 before and know that it works well. And, it's still in pretty good condition. Looks like I'll be hoisting it up to the top of my tower soon.

Many thanks to all who have offered their input and help without berating me for my lack of knowledge. You've also helped broaden my understanding on the subject for the future. Thanks again.

prcguy · May 28, 2015

You can lower the individual dipole frequency by installing a screw or other metal to the center of each dipole end to lengthen it. The easiest thing to do is drill through the element and tap for maybe a # 6 or # 8 screw and adjust the length to resonate where you want.
prcguy

DB-304 Wiring Harness

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