wire dipole for 2mt/70cmt help needed
- WARLOCK
- Top Poster
- Posts: 1414
- Joined: 04 Jun 2008, 08:27
- Call Sign: 26TM134
- Location: cambridgeshire
wire dipole for 2mt/70cmt help needed
i am thinking of putting a wire dipole for 2mt and 70cmt , i have seen people say 18 inches up and 18 inches down would this be about right ???
- DX-Digger
- Top Poster
- Posts: 1092
- Joined: 27 Jul 2009, 22:01
- Call Sign: TM205
- Location: ... - --- -.- . --- -. - .-. . -. -
Re: wire dipole for 2mt/70cmt help needed
1/2 wave dipole (feet) = 468 / frequency in MHz.
:.
468/145MHz = 3.227ft =38.7inches so aprox 19 5/8" inches each leg.
468/435MHz = 1.075ft 12 3/4 inches so 6 3/8" inches each leg of dipole.
You will have to trim it for exact match I wouldnt use thin wire though I would use say 10mm or 3/8" aluminium tube the thicker the tube the wider the bandwidth it covers and the shorter it will need to be trimmed for a good match.
Hope that helps
:.
468/145MHz = 3.227ft =38.7inches so aprox 19 5/8" inches each leg.
468/435MHz = 1.075ft 12 3/4 inches so 6 3/8" inches each leg of dipole.
You will have to trim it for exact match I wouldnt use thin wire though I would use say 10mm or 3/8" aluminium tube the thicker the tube the wider the bandwidth it covers and the shorter it will need to be trimmed for a good match.
Hope that helps
ʎɐqǝ uo pɹɐoqʎǝʞ ɐ ʎnq ı ǝɯıʇ ʇsɐן ǝɥʇ sı sıɥʇ
- ch25
- Top Poster
- Posts: 1679
- Joined: 03 Dec 2016, 11:07
- Call Sign: Lemmy
- Location: Poland
Re: wire dipole for 2mt/70cmt help needed
I recommend that solution:
Chris
Chris
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...
- WARLOCK
- Top Poster
- Posts: 1414
- Joined: 04 Jun 2008, 08:27
- Call Sign: 26TM134
- Location: cambridgeshire
Re: wire dipole for 2mt/70cmt help needed
Thanks Chris ,i know this makes me look thick but can you please give me a little more details as to build this antenna , I do not understand the driven/sleeve elements ???
from George - warlock
from George - warlock
- ch25
- Top Poster
- Posts: 1679
- Joined: 03 Dec 2016, 11:07
- Call Sign: Lemmy
- Location: Poland
Re: wire dipole for 2mt/70cmt help needed
I built this antenna from 1/4 inch copper brake pipe widely available.
2 plastic water pipe pieces to keep sleeve elements in proper distance.
You just drill 2 holes in plastic pipe and put copper elements through.
You connect coax to longer elements, hot to the top, braid to bottom. Do not forget to put some ferrite clamp-on cores on coax. We do not want it to be a part of antenna.
Chris
2 plastic water pipe pieces to keep sleeve elements in proper distance.
You just drill 2 holes in plastic pipe and put copper elements through.
You connect coax to longer elements, hot to the top, braid to bottom. Do not forget to put some ferrite clamp-on cores on coax. We do not want it to be a part of antenna.
Chris
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...
-
- Top Poster
- Posts: 1098
- Joined: 10 Jun 2007, 22:41
- Call Sign: G4RMT
- Location: North East Suffolk
- Contact:
Re: wire dipole for 2mt/70cmt help needed
The ¼ wave for 2m is a surprisingly good match for a ¾ wave on UHF - very simple to produce, and very cheap.
As for ch25's design - it is a ¼ wave for 2m, with two parasitic half waves for UHF - I'm not quite sure what the radiation pattern would be, but certainly not circular - not sure what it's advantages are - it doesn't appear to have too many advantages, and mounting it would be interesting?
why do you recommend it?
As for ch25's design - it is a ¼ wave for 2m, with two parasitic half waves for UHF - I'm not quite sure what the radiation pattern would be, but certainly not circular - not sure what it's advantages are - it doesn't appear to have too many advantages, and mounting it would be interesting?
why do you recommend it?
- ch25
- Top Poster
- Posts: 1679
- Joined: 03 Dec 2016, 11:07
- Call Sign: Lemmy
- Location: Poland
Re: wire dipole for 2mt/70cmt help needed
Just quick modelling in Mmana.
145 MHz dipole will give 75 Ohm, j6 1.5 SWR. Low elevation.
Same dipole on 432MHz 78Ohm, j-52 2.5 SWR. 48 degrees elevation.
GP with 90 degrees radials is even worse.
It matters on RX too.
Antenna I suggested can be tuned both bands. Omni radiation.
How to build? It looks like that: http://sp-hm.pl/thread-2666.html
Also look at radiation pattern and Z and j
Chris
145 MHz dipole will give 75 Ohm, j6 1.5 SWR. Low elevation.
Same dipole on 432MHz 78Ohm, j-52 2.5 SWR. 48 degrees elevation.
GP with 90 degrees radials is even worse.
It matters on RX too.
Antenna I suggested can be tuned both bands. Omni radiation.
How to build? It looks like that: http://sp-hm.pl/thread-2666.html
Also look at radiation pattern and Z and j
Chris
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...