br0adband
Member
I am interested in building 2 antennas specifically for CivAir and MilAir monitoring duties. As I live in an apartment in a building with no ability to get an antenna outside in most any respects I - like so many other apartment dwellers - am forced into finding indoor solutions of most any kind and hoping for the best. I've been toying with the idea of making a funky mount of some kind with clamps to get an antenna outside my window and uses the frame of the window itself as part of the mount but I haven't moved forward on that idea.
I was also thinking about building a discone cut for about 118 MHz on the low end but as an indoor antenna that would end up being rather large and the Wife would most likely have a problem with it herself.
Anyway, I've been doing research into different antenna types and I'm well aware of how a dipole works and the fact that it's used as "the reference" in terms of antennas and performance. I also understand how a 1/4 wave ground plane works (quite well in my experience) as I built one of those very simply homebrew versions using an SO-239 chassis mount, some screws and nuts, and coat hangers and so far it's worked better than I imagined it would. I haven't even soldered all the parts together and I have several elements cut for various frequencies that I just swap out as the main radiator whenever I'm interested. Typically I just leave the 150 MHz element in place (per the original design) and I haven't bothered to add the parasitical elements for 450/800 MHz per the original design which you can find at the link below yet I still get great performance from those bands when I scan them:
http://www.qsl.net/n4yek/scanner/antenna.pdf
But I am wanting to focus more on CivAir and MilAir nowadays. I see that "blade" design antenna by DPD Productions (link here) and while I know the owner of that company has a great reputation and I'd love to have one of those it's simply not possible at this time so I figured I'd try to emulate it with a homebrew version. According to the math, a 5/8 wave monopole for ~127 MHz would be 55.3 inches in length; the DPD blade antenna claims a length of 60" so I'm going to assume (oops, assumption incoming) that the element inside is a ~55 inch one allowing for the housing it's encased in to make up the rest of the length top and bottom (2-3" or so), or something very close to those dimensions.
Also, the specs note that there is gain of 2.6 dBi for that blade antenna, and while I'm not an expert on antenna design by any length, the research that I've done in the past few weeks points to 5/8 wave antennas actually having a slight bit of gain over a traditional dipole at the same frequency. If that's the case, and I make such a beast properly, I should expect to get better performance (another assumption) over making a standard dipole for ~127 MHz or even a 1/4 wave ground plane for that frequency as well.
Am I just nuts here or would someone that's far more knowledgeable about antennas correct me on that assumption if I'm wrong? I mean, again, I'd love to have a really nice commercially produced antenna, sure, and help keep people in business but right now that's not something I can do so, in the effort to try and squeeze out the best performance from what I have access to (wire, some pipes - got a 58" long 1" diameter piece of aluminum pipe that I'm going to try out here later, etc).
Also, is there a requirement - if I go the 5/8 wave route - to have a ground plane because I saw a design that suggests matching the 5/8 wave element with at least three 1/4 wave elements for the ground plane.
And lastly: with this particular setup, either with or without the ground plane, should/would I require a matching transformer or balun for using the coax feed line, or can I just attach the coax leads to the element(s) and that's that?
Yeah, I know I can just build this and be done with it and hope for the best but I figured hey, can't hurt to ask and see what advice or suggestions I get back.
Last thing: I'd be doing this same type of build cut to ~300 MHz as well, so... based on what's offered (if anything) for the 127 MHz variant I would assume (DOH!) that it would work exactly the same, just at the different design frequency... right? Right?
Thanks for any input, it's greatly appreciated.
I was also thinking about building a discone cut for about 118 MHz on the low end but as an indoor antenna that would end up being rather large and the Wife would most likely have a problem with it herself.
Anyway, I've been doing research into different antenna types and I'm well aware of how a dipole works and the fact that it's used as "the reference" in terms of antennas and performance. I also understand how a 1/4 wave ground plane works (quite well in my experience) as I built one of those very simply homebrew versions using an SO-239 chassis mount, some screws and nuts, and coat hangers and so far it's worked better than I imagined it would. I haven't even soldered all the parts together and I have several elements cut for various frequencies that I just swap out as the main radiator whenever I'm interested. Typically I just leave the 150 MHz element in place (per the original design) and I haven't bothered to add the parasitical elements for 450/800 MHz per the original design which you can find at the link below yet I still get great performance from those bands when I scan them:
http://www.qsl.net/n4yek/scanner/antenna.pdf
But I am wanting to focus more on CivAir and MilAir nowadays. I see that "blade" design antenna by DPD Productions (link here) and while I know the owner of that company has a great reputation and I'd love to have one of those it's simply not possible at this time so I figured I'd try to emulate it with a homebrew version. According to the math, a 5/8 wave monopole for ~127 MHz would be 55.3 inches in length; the DPD blade antenna claims a length of 60" so I'm going to assume (oops, assumption incoming) that the element inside is a ~55 inch one allowing for the housing it's encased in to make up the rest of the length top and bottom (2-3" or so), or something very close to those dimensions.
Also, the specs note that there is gain of 2.6 dBi for that blade antenna, and while I'm not an expert on antenna design by any length, the research that I've done in the past few weeks points to 5/8 wave antennas actually having a slight bit of gain over a traditional dipole at the same frequency. If that's the case, and I make such a beast properly, I should expect to get better performance (another assumption) over making a standard dipole for ~127 MHz or even a 1/4 wave ground plane for that frequency as well.
Am I just nuts here or would someone that's far more knowledgeable about antennas correct me on that assumption if I'm wrong? I mean, again, I'd love to have a really nice commercially produced antenna, sure, and help keep people in business but right now that's not something I can do so, in the effort to try and squeeze out the best performance from what I have access to (wire, some pipes - got a 58" long 1" diameter piece of aluminum pipe that I'm going to try out here later, etc).
Also, is there a requirement - if I go the 5/8 wave route - to have a ground plane because I saw a design that suggests matching the 5/8 wave element with at least three 1/4 wave elements for the ground plane.
And lastly: with this particular setup, either with or without the ground plane, should/would I require a matching transformer or balun for using the coax feed line, or can I just attach the coax leads to the element(s) and that's that?
Yeah, I know I can just build this and be done with it and hope for the best but I figured hey, can't hurt to ask and see what advice or suggestions I get back.
Last thing: I'd be doing this same type of build cut to ~300 MHz as well, so... based on what's offered (if anything) for the 127 MHz variant I would assume (DOH!) that it would work exactly the same, just at the different design frequency... right? Right?
Thanks for any input, it's greatly appreciated.