Commscope DB-264 on 2 meter repeater

[iceman977th]

Our club was given a DB-264 that was left on the radio tower we are actually moving to (it was taken off before we knew it existed, and the station engineer said we were welcome to it, just have to pay to have it put back up) I used a tuner to test it, and it is metering 1.5:1 at 146.550 which is not far off from our repeater transmit of 146.940. Is there any way to tune the DB-264 so that the SWR drops down a little lower at our transmit? I know the DB-224's are designed for different bands but I'm not sure about the 264.. plus, it was free to us.

 

[prcguy]

There is more to an antenna than the VSWR. On a folded dipole the phasing harness is a specific length for the frequency it was made for and there is specific spacing between dipoles. Use it at a higher or lower frequency and it can cause an upward or downward tilt to the radiation pattern. I would want to know what that is before putting it into amateur service because it might not work out.

 

[chief21]

If I recall correctly, the DB-224 antennas were offered in different sub-models (-A, -B, etc.), each with a 10 MHz spread (more or less). I'm pretty sure that the -E variant was offered for 138-150 MHz. To my knowledge, they are not adjustable, and the 1.5:1 is most likely well within original factory spec. If you have the original Decibel version, it's a keeper. Most say that the latest ones have issues.

 

[902]

The 264, like the 224, is pretty wide, and, unless you've taken down a MARS, CAP, or other 2 meter repeater antenna, the chances that your antenna is properly resonant on 2 meters is pretty much zero. The 264s are no longer built, so you've got something to hang onto. However, the phasing harness will determine your vertical radiation pattern. Even though your VSWR is acceptable (do not waste your time tweaking it to perfection), the out-of-band harness may send your signal up, or down, at various electrical tilts because of the frequency it was designed for. You'll load up fine. Since you're spending the money on a rigging crew, add some extra and buy yourself a new antenna that's designed to work on your frequency range. Otherwise, it's like spending all kinds of money on a used car. You don't know if you're inheriting someone else's problems.

Antennas have a lifespan, and if that one was flying up there before, it may have latent problems YOU will need to deal with. Get yourself some new cable, too. Nothing works better than a fresh install.

Keep your eyes open for quality control issues on DB products (or whomever makes then these days). Don't schedule a climb until you have an antenna that's "perfect" for your needs.

 

[iceman977th]

There is more to an antenna than the VSWR. On a folded dipole the phasing harness is a specific length for the frequency it was made for and there is specific spacing between dipoles. Use it at a higher or lower frequency and it can cause an upward or downward tilt to the radiation pattern. I would want to know what that is before putting it into amateur service because it might not work out.

Yeah, I know the harness is a big factor in the antenna's performance. I'll have to look a little further into it and see exactly which model I have, I don't see much info on them compared to the 224's.

If I recall correctly, the DB-224 antennas were offered in different sub-models (-A, -B, etc.), each with a 10 MHz spread (more or less). I'm pretty sure that the -E variant was offered for 138-150 MHz. To my knowledge, they are not adjustable, and the 1.5:1 is most likely well within original factory spec. If you have the original Decibel version, it's a keeper. Most say that the latest ones have issues.

I didn't think they were, especially with the harness mounted internally, but I figured it was worth an ask. Yeah, there's not a lot of info on different variations of the 264 like there is with the 224.

The 264, like the 224, is pretty wide, and, unless you've taken down a MARS, CAP, or other 2 meter repeater antenna, the chances that your antenna is properly resonant on 2 meters is pretty much zero. The 264s are no longer built, so you've got something to hang onto. However, the phasing harness will determine your vertical radiation pattern. Even though your VSWR is acceptable (do not waste your time tweaking it to perfection), the out-of-band harness may send your signal up, or down, at various electrical tilts because of the frequency it was designed for. You'll load up fine. Since you're spending the money on a rigging crew, add some extra and buy yourself a new antenna that's designed to work on your frequency range. Otherwise, it's like spending all kinds of money on a used car. You don't know if you're inheriting someone else's problems.

Antennas have a lifespan, and if that one was flying up there before, it may have latent problems YOU will need to deal with. Get yourself some new cable, too. Nothing works better than a fresh install.

Keep your eyes open for quality control issues on DB products (or whomever makes then these days). Don't schedule a climb until you have an antenna that's "perfect" for your needs.

I wish I could say we were able to buy an antenna, this antenna was literally given/donated to the club by the radio station because it was left on the tower. I would ideally like to buy one, but the best hope we have is someone buying a new DB224-E and trading us for the 264. (So, that is an option, if someone is interested) We were also gifted a Stationmaster but I highly doubt it is a lower split and it didn't look like the coax on the end was in good shape when I looked at it.

 

[mmckenna]

You do have other options.
You could disassemble the antenna and just use one of the elements. No real gain, but it'll have a known radiation pattern and will get your repeater on the air. Just don't expect a big coverage area.

Or, take it apart and give 4 hams each a nice broadband VHF antenna.

Or, take it apart, inspect it all, and build new phasing harnesses for it.

But yeah, tower crew costs, get a new antenna that's going to be reliable and do what you want.

 

[12dbsinad]

Yeah, I agree with PRC on the phasing harness. Also, even though you "think" you can get acceptable VSWR, you're also not asking it to perform well under full duplex operations when just testing VSWR. A antenna can go bad pretty quickly when one is trying to apply RF power to the antenna while RX'ing at the same time (ask me how I know) and issues can arise simply due to the age of the antenna and phasing harness condition. I've seen brand new staionmasters fail under full duplex, desense like crazy due to poor solder joints internally.

Everyone thinks they can just throw up any old antenna and have it work full duplex, "because it worked on my home base for 30 years" to realize they have more crunchies than Cap'n Crunch cereal.

 

[iceman977th]

Yeah, I agree with PRC on the phasing harness. Also, even though you "think" you can get acceptable VSWR, you're also not asking it to perform well under full duplex operations when just testing VSWR. A antenna can go bad pretty quickly when one is trying to apply RF power to the antenna while RX'ing at the same time (ask me how I know) and issues can arise simply due to the age of the antenna and phasing harness condition. I've seen brand new staionmasters fail under full duplex, desense like crazy due to poor solder joints internally.

Everyone thinks they can just throw up any old antenna and have it work full duplex, "because it worked on my home base for 30 years" to realize they have more crunchies than Cap'n Crunch cereal.

Understood. That's why I wanted to ask here. I would think I'd be okay, but rather do it the right way and not have to pay for another climb in a few years.

So that being said.. DB264-A for trade to a DB224-E or equal value/antenna.

 

[trooper890]

have seen 264A’s used in the upper part of the 2M band (147) with no major issues beyond a slightly higher VSWR. Have run years just fine.

I do agree though, with the other commenters (lot of experience speaking) and YMMV as there are many variables.

 

[fineshot1]

A nice and easy way to tweek the resonance for lowest swr if you have all other issues taken care of.

decibel db 224 antenna - Bing

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[902]

Repeater builder has a lot of data on how to modify a DB-224 and how to MAKE a proper length phasing harness. You WILL need 75 ohm and 35 ohm cable - get the kind that DOES NOT have foil shielding (!!!!!). The biggest bug in making one of these is sealing the junctions. The manufacturers encapsulate these junctions with plastic. You'll need to improvise something. Then, make the elements resonate using a SA/TG with a return loss bridge or VNA. You do that by drilling and expanding the length with a stainless bolt and nuts. Use anti-oxidant. I can't give you a link because there are more than one articles there describing it. Use the info for a DB-224. They are basically the same except for a ruggeder construction. IF water gets into your harness anywhere, your antenna and coverage goes to crap. Literally.

This could be a good club project, especially if you have junior rocket scientists as members (what hammie club doesn't?). Remember, it's very important to NOT get foil shielding (others and I have explained why in other posts, search those - if your geniuses object to that concept, you will be unpleasantly surprised in full duplex mode). Sealing the connections and potential sites that can wick water into the braid or center conductor is extremely important.

If you choose this route, good luck! I did this once and it was somewhat fun, but also somewhat frustrating.

You MIGHT also try to buy the phasing harness from whomever is making the 224s now. (Yes, I know you have a 264). You still out-of-pocket, but you're buying new. Then do the return loss adjustment of the loops with bolts to make them resonant length.

Modify a Decibel DB-224 for the 2-Meter Ham Band

Antenna Systems Information (Ctrl+F 224)

 

[prcguy]

Most phasing harnesses are made of 75 ohm coax and RG-11 with F compression connectors and "T"s will make a fine harness. DB Products is the only company I've seen that uses different types of coax in the harness.

Repeater builder has a lot of data on how to modify a DB-224 and how to MAKE a proper length phasing harness. You WILL need 75 ohm and 35 ohm cable - get the kind that DOES NOT have foil shielding (!!!!!). The biggest bug in making one of these is sealing the junctions. The manufacturers encapsulate these junctions with plastic. You'll need to improvise something. Then, make the elements resonate using a SA/TG with a return loss bridge or VNA. You do that by drilling and expanding the length with a stainless bolt and nuts. Use anti-oxidant. I can't give you a link because there are more than one articles there describing it. Use the info for a DB-224. They are basically the same except for a ruggeder construction. IF water gets into your harness anywhere, your antenna and coverage goes to crap. Literally.

This could be a good club project, especially if you have junior rocket scientists as members (what hammie club doesn't?). Remember, it's very important to NOT get foil shielding (others and I have explained why in other posts, search those - if your geniuses object to that concept, you will be unpleasantly surprised in full duplex mode). Sealing the connections and potential sites that can wick water into the braid or center conductor is extremely important.

If you choose this route, good luck! I did this once and it was somewhat fun, but also somewhat frustrating.

You MIGHT also try to buy the phasing harness from whomever is making the 224s now. (Yes, I know you have a 264). You still out-of-pocket, but you're buying new. Then do the return loss adjustment of the loops with bolts to make them resonant length.

Modify a Decibel DB-224 for the 2-Meter Ham Band

Antenna Systems Information (Ctrl+F 224)