Help with a 4-bay antenna issue

Several years ago, I read on the 'net that when the coax harnesses on a 4 bay antenna like the one in the picture get lossy, the match stays pretty good, but the radiation pattern starts going off the ends instead of horizontal. I have been searching for this information, regarding an issue we are having. I've been trying to tell people this may be a possibility for reduced range, but without proof, I may as well be talking to the repeater cabinet.

Any help would be appreciated.
Thanks.

Quite a few things can happen to a phasing harness. I recently pulled a DB-224-like antenna from a site and replaced it with a new DB-224 antenna. The coverage improvement was dramatic.

So, what could possibly go wrong?

• Water incursion - rain wicks into the braid or center conductor and changes the characteristics of the cable
• Lightning breaking down the dielectric
• Pollution also changing characteristics - I had a UHF open dipole mounted on the roof of a building with a trash incinerator. The soot from the incinerator and the adjacent highway bonded to the aluminum and had to be stripped with phosphoric acid and Brillo pads.
• UV breakdown to the insulation.
• Bugs/rodents.

Anyway, I just received my order from "The Wireman." I am rebuilding a DB-224 into a smaller two-bay DB-222 antenna and making my own phasing harness from scratch. We'll see if it's less noisy than the Diamond that's on the repeater right now. I'm getting really bad duplex noise, probably from the joints where the sections of the Diamond join together. Wish me luck.

There's a lot of stuff on Repeater-Builder.com.

The Repeater Builder's Technical Information Page™ --> Antenna System Information --> about half-way down the page to DB-224.

The phasing harness is basically a 4-way power divider made for a specific frequency. You can disconnect the harness from one element at a time and connect to a wattmeter with load and measure the power at each branch. Then measure the power into the harness and each branch should deliver close to 1/4 the power put into the harness.
prcguy

Thanks for all the help.
I've been suggesting for almost 4 years to swap out the harness on this antenna for a while as a solution. We will try the things you suggested prcguy. The repeater and cans are great, went over them real good.

Purchasing a new phasing harness is the best option. It will match your antenna best and probably provide the best performance. Also, if there are issues, you'll only have one neck to ring (and it shouldn't be yours!).

It is possible to make your own, but it isn't that easy. The various lengths must be correct for your operating frequency. Also, there are two different types of coax that make up the harness (and both are different than what you use to connect the harness to your radio/repeater/duplexer. The antenna as provided has a 50 ohm impedance. The phasing harness is made up of some lengths of 75 ohm coax and other lengths of 35 ohm coax.

These lengths rely not only on those coax's impedance, but also the velocity factor your specific coaxes has. This can cause the lengths you require to not match those provided by the antenna provider or you found using a Google search. Those lengths will be correct, but only if you have the exact coax the source used (I'm not saying that both you and your source used RG-11 for the 75 ohm coax, for example, but your RG-11 was from the exact same manufacturer - perhaps even made in the exact same batch as your source's coax).

While the RG-11 style 75 ohm coax is pretty easy to find, the 35 ohm coax isn't that easy to find. It is available, but most likely won't be available locally, even most internet sources won't have it. The RG-83 from this source should be the right type. The WireMan - Coaxial Cable

A Better solution would be buying an antenna that does not have the phasing harness exposed to the elements. Even after replacing the harness, it will eventually need to be replaced in the future.

I've bought used DB Products over 30yrs old and the harness is just fine, so they should live a good long life. The coax used by DB Products and others has silicon grease flooded into the braid so it doesn't suck up moisture when compromised.

For some purposes like high mountain top repeater sites it hard to beat an all metal exposed dipole array. I've visited many repeater sites after major storms only to find many fiberglass antennas on towers are now just splinters on the ground and the worst thing that happens to dipole array's is the mast may bend a little.

The dipoles should be close to 50 ohms so you should be able to make a phasing harness from RG-11 and tune the coax lengths with an MFJ antenna analyzer.
prcguy

kayn1n32008 said:

A Better solution would be buying an antenna that does not have the phasing harness exposed to the elements. Even after replacing the harness, it will eventually need to be replaced in the future.

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prcguy said:

I've bought used DB Products over 30yrs old and the harness is just fine, so they should live a good long life. The coax used by DB Products and others has silicon grease flooded into the braid so it doesn't suck up moisture when compromised.

For some purposes like high mountain top repeater sites it hard to beat an all metal exposed dipole array. I've visited many repeater sites after major storms only to find many fiberglass antennas on towers are now just splinters on the ground and the worst thing that happens to dipole array's is the mast may bend a little.

The dipoles should be close to 50 ohms so you should be able to make a phasing harness from RG-11 and tune the coax lengths with an MFJ antenna analyzer.
prcguy

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Oh you are preaching to the choir on exposed dipole arrays. I mean an internal phasing harness like on Sinclair and Bluewave antennas, not some crap fibreglass vertical POS.

prcguy said:

I've bought used DB Products over 30yrs old and the harness is just fine, so they should live a good long life. The coax used by DB Products and others has silicon grease flooded into the braid so it doesn't suck up moisture when compromised.

For some purposes like high mountain top repeater sites it hard to beat an all metal exposed dipole array. I've visited many repeater sites after major storms only to find many fiberglass antennas on towers are now just splinters on the ground and the worst thing that happens to dipole array's is the mast may bend a little.

The dipoles should be close to 50 ohms so you should be able to make a phasing harness from RG-11 and tune the coax lengths with an MFJ antenna analyzer.
prcguy

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DB had some issues back in the 90's with their VHF phasing harnesses when it came to water intrusion. I've got an era 224 that makes all sorts of noise when it's wet...to the point it'll keep the Mastr III it's connected to keyed for additional 10-30 seconds. When it's dry, no worries.

Noise on the input

W5PKY said:

DB had some issues back in the 90's with their VHF phasing harnesses when it came to water intrusion. I've got an era 224 that makes all sorts of noise when it's wet...to the point it'll keep the Mastr III it's connected to keyed for additional 10-30 seconds. When it's dry, no worries.

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So would you categorize this as noise on the input? Would you categorize the sound as constant, never changing?

Here's the deal. Strong signals are fine, but weak signals are covered up with a constant noise that always sounds the same. A decent buzz. Higher than an ac transformer type buzz. The weaker the signal, the more the buzz covers up the incoming station. Someone who works on radio systems for a living went up there with all his equipment, and said "Everything in the cabinet is working fine, you got noise on the input, I'm outta here".

One of the reasons that makes me ponder my theory about lossy harness changing the radiation pattern is that handhelds on the ground floor of this 20 story building, directly under the site, are loud and clear, and can even bring the repeater up with no antenna on the radio. This goes against all I've thought about being directly under a base station vertical with a radio.

I built a new phasing harness for a 2-bay antenna over the weekend using 75 and 35 ohm cable and the formulas I got from Repeater-Builder. For 100 W out, the meter on the Bird barely moves for reflected power, so I probably did it right. The drawback is that the ends aren't flooded, although they're wrapped with Scotch 88 and doused in Scotchkote. I'll probably have to replace it at some point. I used silver RF Industries crimp connectors and a silver T. I scrubbed the antenna elements themselves with phosphoric acid ("naval jelly") and soap pads. There's no soot or gunk on them. And, I used oxide inhibitor on the terminal connections. At least until moisture wicks in, I should have the "perfect" DB-222 type 2-bay antenna.

My duplexer went to the factory for refurb because it wouldn't tune down to 145 MHz. As it turns out, one of the piston/finger-stock assemblies was replaced and the thing was professionally aligned and locked down at the factory. So that's good. Also a new length of about 30 feet of 1/2" LDF with new connectors.

All that said, I put it into duplex service with a popular amateur grade repeater and was getting noise when the transmitter activated. At this point, I'm suspecting two things: 1) the transmitter (nothing more than a mobile radio without the control head) is noisy; and/or 2) the receiver is poorly shielded and is too close to the near-field of the antenna (separation is about 15 feet above, and a little bit over).

Wyandotte, my noise is just like yours - a raspy buzzing on transmit with desense, but no noise on receive. Using an iso-T, It takes about 10 dB more signal to overcome the noise between transmitter off and transmitter on.

It might be your repeater (after a point, what else is left?).

I have a Hamtronics receiver I built into an RF-tight box with bypass capacitors, etc., and an Icom IC-910H to use as transmitter. Those should be a known quantities. What I'm going to do on my end is try a new receiver and transmitter combination to see if it's the repeater itself. If I had a spectrum analyzer, I could have looked at the repeater itself and ruled that out (but I don't). I'll let you know what I find. We may have the same issue. Who knows, we may have the same repeater.

Needing an extra 10db to overcome noise between no transmit and to transmit is NOT good. 10dB is a big difference. I would suggest ditching the Fusion machine and putting in something quality built.


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kayn1n32008 said:

Needing an extra 10db to overcome noise between no transmit and to transmit is NOT good. 10dB is a big difference. I would suggest ditching the Fusion machine and putting in something quality built.


Sent from my iPad using Tapatalk

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LOL! You're right. But it wasn't the fusion repeater. I'm not naming names at this point because I don't know for sure. It's something to look at and rule out. I just find it ironic that Wyandotte and I seem to have similar issues.

I don't remember who it was, or whether it was here or one of my work contacts who was talking about modern repeaters being nothing more than talkpath blocks. Even though it's less than a year old, I'd probably trade this thing for an intact Micor (or MSF, or Qantar, or Mastr II, or Mastr III, or Mastr V... anything but an MSR) repeater that's been modded to be in spec on the lower part of 2 meters. One can't get past the exasperation of looking inside and finding two mobiles, a switching power supply, an interface board, and a control head board with RG-58 cables (that have since been replaced with RG-400). But that's how they all are today, unless you get something that needs a hand truck to move. I could have built that out of a pair of CDMs, an Astron power supply, an old RC-96 panel, and a few fans.

A man and his hobby :lol:

I built a new phasing harness for a 2-bay antenna over the weekend using 75 and 35 ohm cable and the formulas I got from Repeater-Builder. For 100 W out, the meter on the Bird barely moves for reflected power, so I probably did it right.

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Glad everything worked out with the harness for you.

As an experiment, I built a DB224 clone a couple years ago and had good results. I had to side-mount mine to the tower because the 20+ feet of fence railing I used for a mast seemed too unstable and heavy to secure at the base alone.

The harness was an interesting adventure. I used some 75 ohm RG-6, which had a velocity factor of 83%. For the 35 ohm sections, I simply paralleled two sections of 75 ohm cable.
The high velocity factor resulted in quite a bit of slack that had to be dealt with. The substitution of dual 75 ohm cable for the requisite 35 ohm sections resulted in the mast being very crowded with cables. At one point, there are 4 cables in parallel !

This is something that definitely would not be allowed or recommended for a commercial site, but it's okay for non-critical home-use.

The best advice I can give from my own experience is that if you are going to build your own harness, make sure the velocity factor matches, and buy the 35 ohm cable. Don't substitute.
The 35 ohm cable substitution trick using paralleled 75 ohm cables is too bulky and will only add to the weight and wind loading.

talkpair said:

Glad everything worked out with the harness for you.

As an experiment, I built a DB224 clone a couple years ago and had good results. I had to side-mount mine to the tower because the 20+ feet of fence railing I used for a mast seemed too unstable and heavy to secure at the base alone.

The harness was an interesting adventure. I used some 75 ohm RG-6, which had a velocity factor of 83%. For the 35 ohm sections, I simply paralleled two sections of 75 ohm cable.
The high velocity factor resulted in quite a bit of slack that had to be dealt with. The substitution of dual 75 ohm cable for the requisite 35 ohm sections resulted in the mast being very crowded with cables. At one point, there are 4 cables in parallel !

This is something that definitely would not be allowed or recommended for a commercial site, but it's okay for non-critical home-use.

The best advice I can give from my own experience is that if you are going to build your own harness, make sure the velocity factor matches, and buy the 35 ohm cable. Don't substitute.
The 35 ohm cable substitution trick using paralleled 75 ohm cables is too bulky and will only add to the weight and wind loading.

Click to expand...

I thought about that! I remember reading about paralleling cables, and it would not have been too, too bad with only 2 paper clips (I can imagine your 4!), but in the end, I ordered the 35 and 75 ohm cables from the Wire Man. The only thing I could find locally for 75 ohm cable had a foil layer under the braid, and I didn't want to induce noise. The 35 ohm cable has a very thick center conductor that I had to mill down to fit the RF Industries crimp connectors. The 75 ohm cables have a very thin center conductor that I'm worried about flexion breakage. The commercial cables have a tie-point shielding device and then are potted in epoxy. Every time I've goo'ed up a cable, I've changed its characteristics, so I just went with connectors. Before I permanently put this up, I'll probably add a layer of pitch tape over the center T and look into some kind of goo that won't change the dielectric properties of the cable. Probably take Prcguy's advice on silicone grease.

I made a spreadsheet with the formulas to calculate optimal dimensions, factoring in Vf. I can send it out if anyone wants it (my PM fills up, so use email). The Wire Man cable seems to fit the optimum calculated inter-element spacing just right considering the center frequency between transmit and receive. Their RG-83 and RG-11 both have a Vf of 0.66.

I just had a QSO with one of the local guys who has a spectrum analyzer (I haven't bought one yet, although I tend to buy more test equipment than actual "stuff" for my projects). We're going to get together and take a look at the transmitter to see if it's clean.

It's only a hobby, right?

Hey Wyandotte - If you get a new harness from the manufacturer (you can buy one), make sure you specify exactly which frequency range you're using it for. A 2 meter harness will probably either up or downtilt the vertical beamwidth if you're using it on business or public safety frequencies and vice versa. I'd be happy to send you the spreadsheet and parts list (that I used, at least) if you think you want to take on the project of building your own.

My comment on the silicone grease was not to add any yourself and the original cable in the harness is a special version that has silicone grease flooded into the braid over the entire length of the cable from the mfr. If you nick through the outer sheath on this type of cable its still protected from water sucking up into the braid for awhile.

Instead of making the complicated harness with a combination of 75 ohm and 35 ohm cables, why not measure a single dipole on the mast with an antenna analyzer to see how close it is to 50 ohms. If its real close then making a simpler harness from only 75 ohm RG-11 will be much easier and in the end you will probably not be able to measure any difference from factory stock.

If the dipoles end up being 35 ohms or less then the complicated harness may be required, but I don't think so from past measurements on various antennas like this.
prcguy

902 said:

I thought about that! I remember reading about paralleling cables, and it would not have been too, too bad with only 2 paper clips (I can imagine your 4!), but in the end, I ordered the 35 and 75 ohm cables from the Wire Man. The only thing I could find locally for 75 ohm cable had a foil layer under the braid, and I didn't want to induce noise. The 35 ohm cable has a very thick center conductor that I had to mill down to fit the RF Industries crimp connectors. The 75 ohm cables have a very thin center conductor that I'm worried about flexion breakage. The commercial cables have a tie-point shielding device and then are potted in epoxy. Every time I've goo'ed up a cable, I've changed its characteristics, so I just went with connectors. Before I permanently put this up, I'll probably add a layer of pitch tape over the center T and look into some kind of goo that won't change the dielectric properties of the cable. Probably take Prcguy's advice on silicone grease.

I made a spreadsheet with the formulas to calculate optimal dimensions, factoring in Vf. I can send it out if anyone wants it (my PM fills up, so use email). The Wire Man cable seems to fit the optimum calculated inter-element spacing just right considering the center frequency between transmit and receive. Their RG-83 and RG-11 both have a Vf of 0.66.

I just had a QSO with one of the local guys who has a spectrum analyzer (I haven't bought one yet, although I tend to buy more test equipment than actual "stuff" for my projects). We're going to get together and take a look at the transmitter to see if it's clean.

It's only a hobby, right?

Hey Wyandotte - If you get a new harness from the manufacturer (you can buy one), make sure you specify exactly which frequency range you're using it for. A 2 meter harness will probably either up or downtilt the vertical beamwidth if you're using it on business or public safety frequencies and vice versa. I'd be happy to send you the spreadsheet and parts list (that I used, at least) if you think you want to take on the project of building your own.

Click to expand...

And another thing, the original harness would not be using a low loss CATV type cable with foam dialectric, it would use the older stuff with the stiff clear dielectric and probably stranded center conductor, otherwise known as a mil version.

If I were duplicating a harness using the 75 and 35 ohm cables with different size center conductors I would not use connectors and instead tin the braid then cut it leaving about 1/4" long, then trim the dielectric about 1/8" long then leave the center conductor about 3/8" long. Then overlap and butt splice solder the center conductors, then use a piece of copper or brass sheet long and wide enough to bridge the tinned braid and solder the braids to the metal sheet.

If the metal sheet is thin enough you could also wrap it into a tube and solder all the way around the shield of each coax completely shielding the junction. Then clean the solder rosin residue and cast the junction in acid free RTV or maybe Epoxy.
prcguy

prcguy said:

And another thing, the original harness would not be using a low loss CATV type cable with foam dialectric, it would use the older stuff with the stiff clear dielectric and probably stranded center conductor, otherwise known as a mil version.

If I were duplicating a harness using the 75 and 35 ohm cables with different size center conductors I would not use connectors and instead tin the braid then cut it leaving about 1/4" long, then trim the dielectric about 1/8" long then leave the center conductor about 3/8" long. Then overlap and butt splice solder the center conductors, then use a piece of copper or brass sheet long and wide enough to bridge the tinned braid and solder the braids to the metal sheet.

If the metal sheet is thin enough you could also wrap it into a tube and solder all the way around the shield of each coax completely shielding the junction. Then clean the solder rosin residue and cast the junction in acid free RTV or maybe Epoxy.
prcguy

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I read a post you made a few years ago that broke down the impedance of each element. Based on the resulting match, the end product says your'e correct.

The way you described is pretty much the way Commscope does it, then they pot it in epoxy. I was thinking about using copper flashing, but I wanted to get mine done during the President's Day holiday (and I'm lazy). It turned out to be fairly solid. I wasn't able to get flooded cable, but I'm fairly satisfied with the result. I used Scotchkote for a sealant. It'll work for a while.

I'm reusing the folded dipoles from an antenna that was resonant on 2 meters. It wasn't a DB-224, but one like it. Not sure who made the original product. It seems someone prior to me put a Cushcraft harness on it intended to be used with half-wave non-folded segments they used to make. The antenna never worked well where it was, and we replaced it with a new DB-224E. The improvement was dramatic. So, the antenna was dumpstered and some scavenger did some dumpster diving to fish it out. I scrapped the harness and only used 2 of the 4 elements.