| Author |
Message |
    
Sixtiesmania
| | Posted on Saturday, October 05, 2002 - 11:33 am: | 
|
Hello all,
I've seen alot of stuff on this forum, and most is very informative. I think the main thing people miss is the basics, ie, good transmiter + quality antenna = great sounding station! BUT the main hassle to alot of people is the $$$ factor, not on the radio part BUT mainly the antenna part, so how can this be addressed to the masses? Antenna prices are such a bloody rip-off for what you get that it would be GREAT if we could get a forum going that is both informative AND cost affective to radio people.
The first thing would be to actually give out the "Hands on" info on basic 3,4,5 elemnt yagis PLUS (most importantly, the section deglected by EVERY webb site) how to buid a gamma match system, with dimensions (NOT the one with a bloody capacitor ••••!) but the classic "slide in & out type" one comprised of two telescoping aluminium sections with a PVC insulating tubing between the 2 sections. Plus the dimensions of the 2 straps. The specs would be needed to be based on say 27.500mhz (like hello, is this a surprise?? and if it is, it is for "recieving" only ..yeah right. ..Please!)
ALSO, some specs for a basic 2-3 element Quad antenna tuned for 27.500 would be VERY appreciated, with full dimensions AND the tuning system (in laymans terms, not NASA lingo) would, I beleive, be HUGELY popular and informative!
I mean, get real, who the hell can justify spending 4-600 dollars plus on a Jo Gunn antenna that has ridiculous gain figures??? (Unless of course Bill Gates OR Rupert Murdoch is into the Freeband!!)
So, let's get's to it and share the info and knowledge to people out there who are craving for this important stuff!
Hope others agree with me.
Cheers
HV 739
Andrew (an Aussie living in US of A! and LOVING every minute!)
73's |
Buck
| | Posted on Saturday, October 05, 2002 - 2:33 pm: |
|
I agree....I have built a very simple vertical this summer that works as well as my Imax. the problem is that it isnt very pretty and it sits right by the hiway(Translation: dosent really bother me but the WIFE HATES IT. I would happily send some plans to anyone that wants them just email and ask. I would love to build a good 3 or 4 element beam antenna to put on my tower Im going to build this winter. Anyone got any good Ideas??? |
Marconi
| | Posted on Sunday, October 06, 2002 - 10:22 am: |
|
Welcome to the U.S. Andrew. Your request is not as easy to grant as you expectations are to make. Just finding materials that will fit in making a yagi or quad antenna can be a pain. The problem is finding hardware and tubing for mounting and assembly.
You mention the gamma match in a simplistic manner when you say, "...(NOT the one with a bloody capacitor !)." If you want one to work properly, without a lot of losses, it has to be specific in design, using good materials. You can make one out of coax for that matter, but you get what you get. BTW, the PVC you mentioned, expletive deleted, serves as the capacitor. You could use match sticks for that matter.
The problem with putting just any old thing up is being able to control the losses as best you can. An antenna can be very complex or very simple. Ground floor design and construction requires a little understanding. Get yourself some books on antennas and start to read and learn about the finer points involved.
Unless one wanted to use his understanding and knowledge together with his skills in the application of physics, why would anyone want to build an antenna from scratch? It is an admirable pursuit, so go for it. If you can build a suitable mast to boom mount, then you can probably build a yagi using the deminsions noted on Maco's website for their antennas. Just pick one out. They work well and the demensions are all there. You can order a gamma from Copper's and it will be just about as good as you can get. For around a $100 bill I would just order the M-103. The gamma is about 1/3 of the prices alone. What a deal.
Go to, Maco Antennas
Have fun,
Marconi |
Sixtiesmania
| | Posted on Sunday, October 06, 2002 - 7:03 am: |
|
Exactly Buck,
I would love to get this info off you, BUT better still, put it on this forum for the masses to enjoy! Come on antenna heads, share the info!!
PS- Please excuse my typo on first message, it should have read "neglected" NOT "deglected"!!
I hate typing, but hate sounding illiterate even more!
Cheers
Andrew
HV 739 |
Znut
| | Posted on Sunday, October 06, 2002 - 11:27 am: |
|
Sixtiesmania,
I just recently built a 2 element quad.
Here are the basic mechanical specs.
The elements are made of 1/2 inch 75ohm aluminum hardline, the type you see attatched to the overhead powerlines to carry cable TV signals. The spreaders that hold the elements are made of 1 1/2" O.D. thin wall PVC. The boom is made of 1 1/2" high pressure (thicker wall) PVC.
The driven element, the one with the coax hooked to it is 35 feet 7 inches. It is capable of about 1 1/2 feet of adjustment but right now it is tuned as high as I can tune it without trimming the loop part. I have it fed at the bottom so it is horizontally polarized (flatside). I wound 9 turns, about 6 or 7 feet of coax into a choke right at the feedpoint to prevent the RF from radiating from the coax itself.
The reflector is 37 feet 4 inches. It is capable of about 3 feet of adjustment.
The boom is 6 feet 6 inches long.
The height is almost 21 feet to the boom. However, the bottom of the elements are only about 8 feet from the roof of my home with metal siding and metal roof. I don't think that is detuning the antenna too much though.
I have about a 1.2 to 1 SWR on channel 20. I don't know for sure if that is where the antenna is most resonant/efficient. It has nice bandwidth. SWR is under 2:1 from 26.45 to 27.65!
I will make a balun when I can get an analyzer on it and tune it more precisely and determine the exact impedance at resonance. I think this will improve the radiation pattern.
I don't really have any info about the gain or pattern other than the fact that it is directional. All of my results are based on DX. I have had some stations come in 5 or more s-units over my A-99. HR 2510's don't have a very nice s-meter. Yes, I do have a switch to do side by side conparison. When I find a local station with a horizontally polarized antenna I may be able to get an idea of what the radiation pattern looks like.
Overall I am very happy with the results. I used it this past Saturday during the DX-A-THON so there are 3 of you who have heard it on the air. 2 during the event Saturday and one other from a contact the week before, see related threads for details.
As promised, here are pictures.
Znut
|
Znut
| | Posted on Sunday, October 06, 2002 - 3:54 pm: |
|
Arrrggghhh,
I've gotta get some better pictures. |
Taz
| | Posted on Sunday, October 06, 2002 - 5:02 pm: |
|
could you take a picture of where the coax screws in? |
Znut
| | Posted on Sunday, October 06, 2002 - 8:00 pm: |
|
When someone with a digital cam comes by. |
Sixtiesmania
| | Posted on Friday, October 11, 2002 - 2:32 am: |
|
Thanks all,
It's getting good now. What is best way to tune a cubical quad antenna?? Do you use a section of 75 ohm coax, if so how much? ie what calculation do you use to get exact length for whatever frequency you are tuning antenna for? Also, can someone put down the specs of a gamma match for 27.400 tuning, ie what lengths, tube size, strap size & distance and the basic setup of the wiring onto the yagi. ec.
Cheers
Andrew |
Marconi
| | Posted on Friday, October 11, 2002 - 12:08 pm: |
|
Andrew, I believe Znut has found success feeding his quad direct with coax. He may find with his new beam that some device in there might be helpful if it is reactive. However, I think with that much spacing and the use of the choke he has in place, he will probably be OK. He and others tell us it is working well and I believe him.
The best way to tune the quad is to trim for center of band, because you should find it close enough to 50 ohms at resonance to get by.
I think I mentioned before that Copper's sells gammas for 11 meters. I think they are pretty reasonable, so consider one of those. Then you will have a blue print to success on you homebrewed yagi. They will work well with 5/8 to 3/4 inch diameter elements, at a distance from the element, of about 4 times the diameter of the element. The capicator rod should probably be about 1/4 the diameter of the element. This is not a detailed plan for a gamma, there are other things to consider and I do not know how to measure them.
Buy yourself a Maco M-103. You will have every thing you need and it is a great little antenna. It sure will take away a lot of frustration from trying to learn and understand from something that may not work, like a homebrew. Get a handle on that one and then use your experience and understanding to go forward.
Marconi |
Znut
| | Posted on Friday, October 11, 2002 - 10:21 am: |
|
Andrew,
I have a good SWR with no matching. You saw my post above, right? Thats literally all I had to do to use the antenna. I do plan on making a balun as soon as I can get a freind to bring over his MFJ antenna analyzer over and I set the resonance to the center of the band and read the true impedance. From what I understand, it will be around 100 ohms, so I will wind a 2 to 1 balun (100 ohms to 50 ohms).
The type of balun I'll be using will be a matching transformer wound on a ferrite core. It will be tapped in such a way that the current is cancelled out on the ground side of the feedpoint so the antenna radiates all the signal and the coax radiates none. This keeps the antenna's radiation pattern clean, and RF off of the feedline and out of the shack(saving the few brain cells left in the radio shack).
If you build one and need more details email me. It took some doing but I got all the info for the balun. It is posted on the forum, I think under Ask The Tech: 2:1 Balun
Znut |
Buck
| | Posted on Saturday, October 12, 2002 - 11:11 pm: |
|
I will post the plans for the omni as soon as I can get them typed up....Possibly tommorrow. Ive been putting in 18 hour days since monday and finally have a day off! |
Buck
| | Posted on Sunday, October 13, 2002 - 8:28 pm: |
|
Homebrew Base Antenna
Parts List
2- 10x ½ Copper tubing
1- ½ Copper end cap
40 of 12 AWG stranded copper wire
1- 1x ¾ SCH 40 PVC pipe
4- 3/16 x 2 Bolts with flat washer, lock washer, and nuts
12- Ring terminals(to fit bolts)
4- Tent stakes
Parachute cord or heavy twine
Soldering iron
Solder
Coax RG-58, RG -8x, or RG-8U
Construction
1. Cut one section of copper tubing 102 long.
2. Solder the end cap on the 102 copper tubing.
3. Slide the 102 copper tubing 6 into one end of the PVC pipe.
4. Using a drill, drill two 7/32 holes through the PVC and tubing.
5. Slide the bolts through the holes and place one ring terminal on the bottom bolt.
6. Slide the full length piece of copper tubing 4 into the PVC pipe
7. DO NOT ALLOW THE TWO PIECES OF COPPER TUBING TO TOUCH!!!!!
8. DAMAGE TO YOUR RADIO COULD RESULT
9. Drill holes and install bolts.
10. Cut 4- 102 pieces of 12 AWG wire. Put a ring terminal on each end of wires.
11. Put ring terminals from one end of the wire on the bottom bolt of the bottom tubing.
12. Strip 6 of insulation from the coax. Do not damage the shield.
13. Put a ring terminal on the center conductor and one on the braid.
14. Attach the center conductor to the top bolt on the 102 piece of copper tubing.
15. Attach the braid to the top bolt of the bottom piece of tubing.
16. Find an open spot in the yard and shove the 10 section of tubing in the ground.
17. Tie enough parachute cord to the 102 wires to reach the ground at a 45 degree angle.
18. Using the tent stakes, put the wires in a N/S/E/W direction and stake at a 45 degree angle.
19. Connect your coax and check SWR. Mine was better than 1.5/1 on all channels
20. Have fun talking on your new antenna
If you have any questions feel free to ask....Post here or email me |
|
