Need help with a 2 meter beam

[tracker1962]

Can anyone tell me who made this 16 element 2 meter beam and maybe a model number.
It was purchased from a Hamfest many years ago.
It has to be 30+ years old easy as I have had it close to 20 years.
I used it for a couple of years and then gave up the hobby.
For over a decade it just spun around freely in the wind with the coax broken.
Got back in the hobby and took it down and noticed that the elements were not "longest to shortest" back to front so I reset the elements as such, longest in the back and getting shorter towards the front.
I get an ok SWR on my simplex that I use the most @ 146.415 but not very good elsewhere.
For a log periodic with so many driven elements in the back (5), I should be doing better.
If I could get some help, I would take it down again and do what needs to be done.
It being some 30 feet long, I don't want to do that too often !
Any help would be greatly appreciated and I came here as I know if anyone has an answer, here is where it will come from.
Thanks in advance.
73 de VE3MTD.

 

[Mudfoot]

Sounds like the elements were spaced correctly in the first place.

 

[Moleculo]

It's not a log periodic; it's a yagi.

I did some googling and came up with a couple of companies that made 16 element 2m yagis, but nothing that was a dead ringer for what you have. can you take a closer picture of the matching section and some of the elements?

BTW, from that distance it sure looks a lot like a Cushcraft 17B2 that is missing one element.

 

[tracker1962]

Well it was never working really well from the start and elements normally go from longest in the back to shortest in the front m42duster.
Moleculo, there is no sign of anything missing on this unit.
No empty holes, no marks of something being there at one point, nothing.
It looks complete but after 20 years of looking for info. we can't find anything.
Attached is a pic of the back door.

 

[Mudfoot]

Yes, I know how yagis work. Your pic did not load on my DROID, so I was going on your assumption that it was a log.

I have a portable handheld log and just about everyone that picks it up points it backwards.

I think Universal Radio has pics of discontinued beams. They might have it listed. If not, I'm confident that someone here has/had one.

 

[tracker1962]

m42duster, the elements were all over the place including one on top being shorter than one on the bottom on the same rung in several places?
Moleculo, here is the whole unit.

 

[tracker1962]

The Cushcraft 17B2 has a gamma this one does not?

 

[KC9Q]

I found it in an old 1982 AES catalog. It is a model 144-148-16 made by KLM. It was marketed as "folded dipole drive" that provides efficent broadband performance.


The specs are as follows:

Coverage: 144 - 148 MHz
Gain: 14.8 dBd
VSWR: 1.2:1 or better
Beamwidth: 16 degrees
Elements: 16
Feed Impedance: 50 ohms unbalanced
Balun: 4:1 Coax, 2 KW
Boom Length/Dia: 20.6' / 1.5"
Weight" 10 lbs
Mast Size: 2"

The 4:1 balun is optional for this antenna.
1982 Price: $89.95USD

There is also a 13 element version Model number 144-148-13LBA that has a forward gain of 15.5 dBd, 28 degree beamwidth, and a 21.5 ft boom length. All other spes are the same. Its 1982 price is $99.99USD and includes the 4:1 Balun

Go figure - more elements, less gain. That's what is published.

I could scan the page in later if you like.

73,
Mike, KC9Q

 

[tracker1962]

Hey Mike.
We might be getting closer?.
Please, please send me what you may have.
marcatrona@hotmail.com
I thought the boom was longer but just measured where I had it when I took it down and 20.6' seems about right.
Mine as you can see does have 16 elements.
Thanks Mike!

 

[KC9Q]

Here's a 3 page pdf. Page 1 and 2 is from the 1979 AES catalog. Page 1 shows the Ordering Code, Page 2 gives the spec for the antenna near the bottom of the page. Page 3 is from the 1982 AES catalog and shows the spec and VSWR curve for the 144-148-13LBA in the upper right hand corner.

73,
Mike, KC9Q

 

[KM3F]

The antenna is a 'BANDPASS" log periodic design.
The feed is 180 degree crossovers feeding dipoles that are staggered tuned in electical length to have a broad bandwidth.
A Balun of sorts is needed to feed it with 50 ohm coax.
The Coax Balun shows quite clearly as does the crossover feed.
The total design is supposed to have a cutoff frequency just below and above the band for which it was designed.
This is where the 'bandpass' function comes from and is usually quite sharp.
The reflector and directors give it the gain.
The hair pin loop on the rear driven element terminates the feed so the antenna will have a good front to back ratio.
The element lengths can be different than the usual Yagi.
In an older VHF - UHF Hand Book out of the UK by JESOP, this design shows up for 6m, 2m and 70cm bands.
Today with FM being vertical and SSB weak signal work being horizontal, few would use such a design for anything but FM or turned the other way for SSB.
So there is no real need for bandwidths that wide per the two modes.
BTW, most weak signal TV antennas were of this design where gain and bandwidth was needed to cover channels 2 to 13.
IMHO, the design has no compeling merits today so no one markets the design, that I know of.
Not saying they don't work so use it if you have it.
Also a Log design is a very complex mathamatical design such that it would take an emense amount of time to tune and determine the pattern from anything but a model or a previously worked out set of plans..
I have run onto the posters antenna while doing internet searches on such a design that I have built form a TV antenna as a 5 elment out of the JESOP book but have not finished the tuning and matching due to time required.
I don't think there is any advantage to the design today over the big Yagis in a single or stacked configurations.
The biggest reason the log antenna design is difficult is the precise phase relationships between the elements vs frequency and impedence.
In this design there is a lot of interaction that makes it hard to get one tuned.
So there you have the results of my research, so far.
Good luck.