| Author |
Message |
    
Xlaxx
| | Posted on Tuesday, April 22, 2003 - 5:41 pm: | 
|
I have done several searches for info. on this particular beam. I have come across the following:
Forward Gain 12 dBi; Rejection 32dB
VSWR 1.3:1 (1-40CH.)
Safety Factor 2000W
Boom Length 4'10"
Wgt. 13.5lbs
Wind Load 2.0 sq. ft.
On the Copper Forum, many have mentioned that the dB gain is 7-8. What are the differences here and what is "real world" dB? dBi? What does dBi mean? The manufacturer states 12dBi.
Also, what breaks most on this beam? The hub? Can I get a replacement if it does break? Copper seems to list a replacement hub but states that it is "Out of Stock",... can one use Moonraker 4 parts?
Sorry about the 20 questions and all,...
Again, much thanks to the Techs, Moderators, and Forum Members!
XLAXX |
Tech833
| | Posted on Tuesday, April 22, 2003 - 9:30 pm: |
|
Hi X,
No parts available, and most Moonraker parts won't fit. The PDL was a true quad, while the Moonraker is not.
What breaks most? Hubs and fiberglass spreader rods. Spray all your plastic/fiberglass parts with auto primer to protect them from UV rays and they will last much, much longer.
The real gain? 12 dBi is not far off, that sounds believable. That would be 10.9 dBd. The 'i' in dBi means Isotropic. The 'd' in dBd means Dipole. So it is gain over an isotropic (theoretical) antenna or gain over a dipole reference. |
Xlaxx
| | Posted on Tuesday, April 22, 2003 - 11:31 pm: |
|
Thanks Tech 833!
Well 10.9dBd is better than 7-8! I guess I'll call it 11dBd. 833 where did you get your readings from?
OK, so I just spray the primer on. Will this affect the PDL's performance in anyway? Do I need to sand anything before? Should I use Penetrox on this as well?
If the PDL was such a great beam,... why did they stop producing them? Many have referred to the PDL as a fantastic antenna/beam.
Thanks
XLAXX |
Crafter
| | Posted on Wednesday, April 23, 2003 - 1:20 am: |
|
Xlaxx you can re-enforce the hub with a piece of 3/4 in plexi-glass but then you need longer bolts up front...Most of the raker parts will work, ie elements and half brackets. I still got a globe if you need parts. I still service quite a few in this area due to wind and ice, but never have had to work on the hubs once I beef it up..The trick I've learned here is pay very close attention to the lenght and size wire you use. I use a clear coat on the fiberglass radials. |
bruce
| | Posted on Wednesday, April 23, 2003 - 7:02 am: |
|
A 2 elem quad with 10 DBD gain ????? PLEASE .... real gain is somewhere around 6 DBD still not bad. |
Tech833
| | Posted on Wednesday, April 23, 2003 - 11:34 am: |
|
Bruce,
We are talking about CB gain. Usually CB gain is about 3 to 6 dB more than ham gain. As you know, ham gain is usually 3 to 6 dB above actual gain. That's not even considering the audio gain....
Truthfully, a 2 element quad should be close to the same gain range as a 3 element yagi, but not quite. 6 dB is a little low for a mono-band quad. Most figures I see are in the 7-8 dB range. Of course, this does not include feed losses, for the most part. People often overlook those. |
bruce
| | Posted on Wednesday, April 23, 2003 - 1:06 pm: |
|
I stand corrected its like coax if you feed the top and allow the ant to be at the bottom the gravatational force acts like a linear and you get coaxal gain.....
Thanks for the correction
Bruce |
de
| | Posted on Wednesday, April 23, 2003 - 10:02 pm: |
|
Re Brucen and Xie...
First Bruce, oops you misread the stats. The gain was in dBi. Meaning that dBd could be just about anything. As to those obscene gain factors Bruce, I was reading somewhere where the PDL II in its original form got the unusual numbers because it was a folded dipole feeding the loop configuration. HMMM I have no comments to make on this. BUT I do know that if you toss out that gamma match garbage and use the base configuration to home brew a standard quad for 10 Meters you get one dang good antenna. AND if you splice two PDL Booms, rebalance the antenna, and use the second boom just to hold a director you can make yourself one hell of a fine 3 element quad for 10 meters. I made a 3 element quad like this once. Rejection out the mind. Even with just guessing spacing for the director the Front to back was great and the forward must have been pretty good given the improved reception. UNFORTUNATELY, I did not conduct any kind of gain testing. May be next time.
Ok Xie have a seat. I hope I do not confuse you. The very first thing you have to know is that antennas do not manufacture power. All they do is focus the power you put into them so that the signal becomes concentrated in a certain pattern making it "Sound" stronger without actually being stronger. dBi and dBd are used to describe the gain of an antenna. dBd is when the beam is compared to a real life quarter wave dipole having little or no gain. DBi is the gain of an antenna compared to a theoretical and or mathemitically perfect dipole in a perfect free space called an isotropic dipole. DBd is a comparison of one real antenna against another real antenna. Dbi is a comparison of one real antenna against a non existant although perfect antenna and how it would function.
The front to back ratio is the ability of the antenna to 'not hear' or reject signals comming from the back. The bigger the number, the bigger the rejection. HOWEVER, this also means that you will need some kind of vertical to hear things rejected by your beam. AND in gaining rejection you have to sacrifice some forward gain. It is a balancing act.
And here is the hard part. Every 3 dB of gain doubles your power. Your PDL2 with a DB gain of 12 will double power 4 times over (12/3). So if you input 4 watts the first 3 db will double it to 8 watts. The second 3 db will double the 8 to 16 watts. The third 3 db will double the 16 to 32 watts. The 4th 3 db will couble the 32 to 64 watts. That would give a multiplication factor of 16 for the antenna (64/4).
HOWEVER, I am with bruce on those DB factors. I seem to remember the PDL 2 having a gain less than 9 db. You might want to check those specs once again.
AS TO HUBS, The plastic hubs break pretty easily. If you cannot find the plastic hubs try to get the the aluminum hubs (a set of 2). They are expensive but then again they do not break. And here is the trick. The plastic hubs act as an insulator between the inner extension arms and the boom. So if you use the aluminum hubs just put a layer of PVC pipe and to insulate the inner extensions from the boom. Use non metalic nuts and bolts as well thru the the holes in the inner extensions OR do as I did and just slip a big shrink tube over the bolt. Using a VOM check to make sure that there is no continuity between the extensions arms and the boom.
I hope that I have not confused you. I have a copy of the assembly manual if you need it.
Enjoy..
DE |
ChillyDog
| | Posted on Thursday, April 24, 2003 - 12:11 pm: |
|
Tech833,
CB gain! That explains so much! After 20 years of RF engineering, I finally understand why CB is different than any other form of radio ...
Very Best Regards,
Bob |
Crafter
| | Posted on Friday, April 25, 2003 - 1:40 pm: |
|
Xlaxx did you get the manual ? |
Xlaxx
| | Posted on Saturday, April 26, 2003 - 10:39 pm: |
|
de-
Thanks for the excellent info.! I understood your explanations. Thanks for setting the record straight.
It would be nice to have a perfect antenna for sure! LOL
Crafter-
This particular beam was purchased from a gentlemen in Omaha, NE. DX431 was talking about this beam on a previous Copper post.
The PDL was sitting in this man's CB shop for about 26 years. It was new, in a non-opened/virgin box with 26 years of dust on top of it. It was on 'hold' for someone who never came to get it.
My buddy here in town has a PDL 2 and it seems to be a very good antenna, also very low-profile for a beam. Anyway, I downloaded some info about it and it said something about plastic hubs. Well, I figured that plastic doesn't last too long outside so I need something to reinforce it. I have not opened up the shipping box yet. I am very excited about it, so no I haven't peeked inside to see if there is a manual or not.
Can I still get the aluminum hubs? Where? What dimensions for the plexi glass?
XLAXX |
de
| | Posted on Sunday, April 27, 2003 - 9:10 am: |
|
Re X...
Per my old assembly book the plastic hubs were 5" by 5"
As to thickness of the plastic glass I would think that 1/2 inch on each side of the element woule be sufficient overkill. If you cannot get 1/2 inch in a single sheet you can put two 1/4 inch thickness together. This should provide sufficient overkill.
Remember when cutting plastic glass do not push the jig saw or the drill bit thru the material. Let the blade cut and the drill bit drill the plastic for you. Take your time.
I hope that you are not going to reproduce the entire antenna yourself. This particular antenna achieved its extra gain because those hoops acted as a folded dipole which fed the loop. You would be hard pressed to manufacture this yourself.
If you want the same basic antenna as the PDL 2 check out Copper line of "Maco" antenna. They have a 2 element PDL 2 look-alike with 12 db gain. The only difference is that the loaded elements are different design--more like the Raker 4.
DE |
Bigbob
| | Posted on Friday, May 02, 2003 - 8:51 pm: |
|
Forget the acrylic sheet(plastic,plexi,etc.)go with polycarbonate sheet(lexan)this material is ten times stronger than plex(1/4" will stop a .38 slug from 25 feet)and get it at a window manufacturer,the lex made for glazing has a built in UV-block.1/2inch lex will stop a 44-magnum,can be used for tow-strap links,but for pdl-11 is a little over kill,plex in any thickness turns very brittle in one year when exposed to sunlight and oxygen.POLYCARBONATE can be sawed,drilled or machined with anything and will not shatter or crack,2 foot by 6 inch piece can be bent in a complete circle,try that with acrylic but wear safety goggles and protective clothing,hope this helps.Big Bob |
de
| | Posted on Saturday, May 03, 2003 - 8:17 am: |
|
RE Biggie....Just curious.
Cost Factor and local availability?
Where? How Much/cost? .
Also just thinking out loud, the local welding shop probably has some scrap square sheet aliminum 1/4 inch thickness or thicker drop offs sitting around gathering dust that they could sell him. A little careful time scratching out the pattern and on the ol jig saw with some PVC and plastic for insuating the spreader elements as required will also fill the bill.
Later
de |
|
