Omi-Directional Homebrew Choice...

[B52outpost]

I am considering one of several antenna designs for my attic. The antenna will not tranmit only receive. The scanner bands desired (order of preferance): 860 Mhz; 453 Mhz; 155 Mhz. I need an omni-directional antenna verses a directional beam like yagi.

1) A 1/2 or 5/8 wave homebrew like the 1/4 wave listed at: http://www.hamuniverse.com/2metergp.html
I do not know what the correct wire lengths would be, so if you know where I might find the correct formala, I sure would appreciate it.

2) A 3-band J-Pole. I'v seen a 2-band (2 meter and 70 cm), but never one for the freq. that I desire. If you know where I might locate the specs, please let me know.

3) Any other homebrew design that I might be overlooking that you can think of? (omni-directional)

Which one would be best? Thanks in advance antenna gurus!

 

[k9rzz]

I think if you cut a grounplane for 155mhz, like on your link, it will receive fine up through 800 mhz.

234/155=1.5ft or 16 inches. A little longer for the radials. Exact measurements not required for receiving. Use good coax and you should hear plenty with it.

 

[N_Jay]

I think if you cut a grounplane for 155mhz, like on your link, it will receive fine up through 800 mhz.

234/155=1.5ft or 16 inches. A little longer for the radials. Exact measurements not required for receiving. Use good coax and you should hear plenty with it.

Stop telling people how well simple antennas work.
You will destroy the market for over-priced "magic" antennas that work from 100 kHz to 1000 MHz with 20 dB of gain (over a dummy load).

(READ: Yes, A simple ground plane, or dipole will work fine. Add an element for each band to make a minor improvement.)

 

[ka3jjz]

Or how about the off center fed dipole that's in our wiki? There's another DIY that had a great discussion in this forum some time ago.

73s Mike

 

[N_Jay]

Or how about the off center fed dipole that's in our wiki? There's another DIY that had a great discussion in this forum some time ago.

73s Mike

Off center fed dipole is basically a random length antenna with a good legend behind it.:roll:

 

[B52outpost]

I think I found what I was looking for at: http://www.qsl.net/w4sat/five8th.htm

A site that has the measurements for 5/8 wave at various Mhz (single band though).
Maybe the site will be of assistance to another.

Thanks for the responses

 

[zz0468]

I think I found what I was looking for at: http://www.qsl.net/w4sat/five8th.htm

A site that has the measurements for 5/8 wave at various Mhz (single band though).
Maybe the site will be of assistance to another.

Thanks for the responses

Odd that the site doesn't give any information about the required matching network, other than to say it's needed. How useful will that be to you?

 

[Don_Burke]

I think I found what I was looking for at: http://www.qsl.net/w4sat/five8th.htm

A site that has the measurements for 5/8 wave at various Mhz (single band though).
Maybe the site will be of assistance to another.

Thanks for the responses

Here is a link for j-pole design:

http://www.hamuniverse.com/jpole.html

Multiband j-poles are designed by making the highest frequency antenna first and building the next highest frequency antenna under it. Keep going down in frequency and building underneath.

J-poles can be pretty narrowbanded, so it will probably be disappointing unless you really need something narrowbanded.

 

[jonny290]

Off center fed dipole is basically a random length antenna with a good legend behind it.:roll:

so true, so true

the impedance varies so incredibly widely over the frequency range that people use it for that the 4:1 balun doesn't do much and for some reason, everybody cuts their OCFD for the FM broadcast band and then complains when their scanner overloads.

now, you absolutely can feed a 1/2 wave antenna at the 300 ohm point but the ocfd rarely does that

 

[knightrider]

For monitoring on the scanners here, I made a simple wire dipole, and put it inside PVC. This is not the OCFD that has been mentioned, but I guess close. I used a PVC Tee to connect the 2 pieces of PVC pipe together which house the wires, and soldered a short piece of coax to the wires, and ran it out the side of the Tee, and through a piece of PVC that was 24" long so I could get it away from the side of the tower. to this coax, I soldered a connector to attach a longer piece to get in the shack. You could attach a single piece to go the full route, and not have any connectors in line if you wanted. This antenna is mounted at about 35' on the side of my tower, and I hear traffic as much as 100 miles away. Mind you, I am in the country, and have a couple miles of flat land before the hills start to form. I cut one for 155.00 Mhz, and one for 300.00 Mhz. I have two scanners and have one setup for each band. I do vey little 800 stuff here, so that was not a concern. I had the PVC already from a couple of plumbing projects, as well as the wire and coax so my investment was actually CHEAP! Now, if I "need" to hear farther, there are 3 VHF, and 2 UHF beams on the top of the tower at 75' I can use to pick out the weak ones, but prefer to use them for Ham Radio...
Knightrider