How about a slight rx-only spin on the classic "RFD", or "resonant feedline dipole"?
With parts left over from my loop-on-ground and dipole-on-ground projects, I had enough to make a slightly different antenna, that is purposely NON-resonant. So far, works great up in the air, and of course, on-ground too.
If you search for "resonant feedline dipole", you'll see that is is basically a quarter-wave of wire attached to the center conductor of a piece of coax (braid not connected), and a quarter wave of coax away, a common-mode-choke is applied. The idea here was to be "resonant" on a single band.
But I twisted that idea a bit to be purposely NON-RESONANT for rx-only use, by using a 9:1 transformer at the coax-to-wire feedpoint junction, and instead of the "feedpoint" being in the center, I offset it by about a 3rd. Like the classic RFD, I *wanted* common-mode interaction to be choked later down the line, so my transformer is sharing a common ground, ie an auto-transformer, one that is NOT ISOLATED.
My objective: 160 to 20m coverage. That means I'm not going to exceed about 30 feet *total* for the antenna itself (coax and wire). This is more important for my on-ground pattern, since exceeding a half-wave at the highest frequency will start to rapidly skew the more or less omni pattern.
Antenna: ( I used what I had laying around. 9-foot coax jumper and a NooElec 9:1 transformer, as set by oem as a shared ground). Here's the layout:
MFJ 915 ferrite choke > 9 feet of RG8X > 9:1 autotransformer > 21 feet of wire
The actual feedpoint isn't critical. Got a 12-foot coax jumper? Use an 18 foot wire. I think any coax jumper in the range of about 6 to 15 feet (and adjusting the length of the wire for a total of 30 feet) will do just fine. Experiment - use a 4:1 if you have that handy, but make sure it is an autotransformer, NOT isolated. Easier to come by anyway.
So far the results are about the same as my on-ground loop. In the air I have much more signal of course. I supported the lightweight Nooelec 9:1 transformer on the coax and wire with a popsicle stick for strength. I think I have additional common-mode choking since my feedline is on the ground. I choked it at the rig too with another ferrite choke, and noticed no major difference.
On ground, my SWR, if that really means anything to this rx-only application is no higher than 4:1, even at 160, where I still hear my squirrely little noisemakers in the neighborhood down low.
Note: I didn't go nuts over this thing. Use a better common-mode-choke like a MyAntennas CMC-0510-R. Perhaps a nicer 9:1 with better specs, or wind your own, but be sure NOT to isolate it. Lots of of transformers from the garden variety "end-fed" antennas that use a 9:1 might be in your drawer right now.
Thumbs up! Aside from hanging it in the air in a variety of configurations, it would also make a nice option for on-ground users that have a small side-yard, maybe just a long planter, and can't have a feedline coming off a regular loop or dipole on ground in the backyard.
With parts left over from my loop-on-ground and dipole-on-ground projects, I had enough to make a slightly different antenna, that is purposely NON-resonant. So far, works great up in the air, and of course, on-ground too.
If you search for "resonant feedline dipole", you'll see that is is basically a quarter-wave of wire attached to the center conductor of a piece of coax (braid not connected), and a quarter wave of coax away, a common-mode-choke is applied. The idea here was to be "resonant" on a single band.
But I twisted that idea a bit to be purposely NON-RESONANT for rx-only use, by using a 9:1 transformer at the coax-to-wire feedpoint junction, and instead of the "feedpoint" being in the center, I offset it by about a 3rd. Like the classic RFD, I *wanted* common-mode interaction to be choked later down the line, so my transformer is sharing a common ground, ie an auto-transformer, one that is NOT ISOLATED.
My objective: 160 to 20m coverage. That means I'm not going to exceed about 30 feet *total* for the antenna itself (coax and wire). This is more important for my on-ground pattern, since exceeding a half-wave at the highest frequency will start to rapidly skew the more or less omni pattern.
Antenna: ( I used what I had laying around. 9-foot coax jumper and a NooElec 9:1 transformer, as set by oem as a shared ground). Here's the layout:
MFJ 915 ferrite choke > 9 feet of RG8X > 9:1 autotransformer > 21 feet of wire
The actual feedpoint isn't critical. Got a 12-foot coax jumper? Use an 18 foot wire. I think any coax jumper in the range of about 6 to 15 feet (and adjusting the length of the wire for a total of 30 feet) will do just fine. Experiment - use a 4:1 if you have that handy, but make sure it is an autotransformer, NOT isolated. Easier to come by anyway.
So far the results are about the same as my on-ground loop. In the air I have much more signal of course. I supported the lightweight Nooelec 9:1 transformer on the coax and wire with a popsicle stick for strength. I think I have additional common-mode choking since my feedline is on the ground. I choked it at the rig too with another ferrite choke, and noticed no major difference.
On ground, my SWR, if that really means anything to this rx-only application is no higher than 4:1, even at 160, where I still hear my squirrely little noisemakers in the neighborhood down low.
Note: I didn't go nuts over this thing. Use a better common-mode-choke like a MyAntennas CMC-0510-R. Perhaps a nicer 9:1 with better specs, or wind your own, but be sure NOT to isolate it. Lots of of transformers from the garden variety "end-fed" antennas that use a 9:1 might be in your drawer right now.
Thumbs up! Aside from hanging it in the air in a variety of configurations, it would also make a nice option for on-ground users that have a small side-yard, maybe just a long planter, and can't have a feedline coming off a regular loop or dipole on ground in the backyard.
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