breadtrk
Member
I have searched for this but can't seem to find any consistent data, just opinions and they are as varied as the wind. Which would be the best for mobile 800 trunking?
Full wave vs 5/8, 1/2, 1/4 ground plane?
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Don_Burke
Member
Topography is a consideration for this.
If you are dealling with mountain top sites, a quarter wave would probably be the best.
In the flatlands, 5/8 wave would probably be the best.
Full wave antennas rarely work well enough at UHF frequencies.
If you are dealling with mountain top sites, a quarter wave would probably be the best.
In the flatlands, 5/8 wave would probably be the best.
Full wave antennas rarely work well enough at UHF frequencies.
AlmostHandy
Member
Ahh, I read that one of them is better for listening to airplanes, because instead of a horizontal plane, it is focused up a little bit, allowing for better range of flying things. I think it was 7/8 wave, but I can't find the article now amongst my unorganized bookmarks. I've been collecting them faster than I can sort them out.
W6KRU
Member
The 1/4 wave will have a fatter lobe and work what you want better. That is why 5/8 have better gain usually. They compress the signal into a shallower lobe.
This would be so much easier with a whiteboard.
This would be so much easier with a whiteboard.
breadtrk
Member
Well, after posting and reading the first reply..... I found the related thread deal at the bottom on the page.. I guess I wasn't searching with the right terms, this has been covered and debated many times on this forum.
I fully understand the radiation lobe patterns for the different antennas, what I had not factored into this was my average terrain. Part of my journey is hilly and part pretty darn flat, so I guess I should mount a 1/4 and a 5/8 and use a switch. They all have their place I guess.
Thanks guys.
I fully understand the radiation lobe patterns for the different antennas, what I had not factored into this was my average terrain. Part of my journey is hilly and part pretty darn flat, so I guess I should mount a 1/4 and a 5/8 and use a switch. They all have their place I guess.
Thanks guys.
AlmostHandy
Member
Hoofy
Member
I would opt for something with some gain if it is just for 800.
a 1/4 wave 800 will only be 3 to 4 inches tall.
a 1/4 wave 800 will only be 3 to 4 inches tall.
prcguy
Member
There is a common misconception that a good aircraft antenna needs to point up in the sky. In reality you want the same thing for air band monitoring as for long distance terrestrial use with as much signal at the horizon as possible. Even with an aircraft at 50,000 ft its only about 9.5 mi overhead and you can talk to it with a paper clip as an antenna. When the aircraft gets 150mi or greater its near the horizon and that's when the low angle antennas start earning their pay.
I think the most common types of 800 antennas are the 3" 1/4 wave whip and various stacked collinear types with a 1/2 wave stacked over a 1/2 wave or a 5/8 over a 1/2 or two 5/8s stacked, etc. These will have up to 3dB more gain than a single 1/2 or 5/8 wave but no more and probably a little less because the phasing coil does not place the top element at the optimum spacing above the bottom element but it does allow both antennas to be fed in phase for some increased gain. There are lots of reasons you don't see a full wave whip except in CB advertisements (lies) and there are lots of other posts that explain this in detail.
prcguy
I think the most common types of 800 antennas are the 3" 1/4 wave whip and various stacked collinear types with a 1/2 wave stacked over a 1/2 wave or a 5/8 over a 1/2 or two 5/8s stacked, etc. These will have up to 3dB more gain than a single 1/2 or 5/8 wave but no more and probably a little less because the phasing coil does not place the top element at the optimum spacing above the bottom element but it does allow both antennas to be fed in phase for some increased gain. There are lots of reasons you don't see a full wave whip except in CB advertisements (lies) and there are lots of other posts that explain this in detail.
prcguy
Don_Burke
Member
Try a quarter wave;it should be good enough.
Depends On The Terrain
If you live in an area that is flat, and the towers aren't that high, the longer colinear antennas may be better.
If you live in a hilly area, anything more than a 1/4 wave or 1/2 wave will simply produce flutter and dead spots because the takeoff angle of the antenna will be too low.
If you live in an area that is flat, and the towers aren't that high, the longer colinear antennas may be better.
If you live in a hilly area, anything more than a 1/4 wave or 1/2 wave will simply produce flutter and dead spots because the takeoff angle of the antenna will be too low.
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