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260’ dipole for all bands
- Thread starter nfsus
- Start date
On odd-harmonic frequencies it should behave okay with just coax feed. Even harmonics would call for a tuner. Don't know how efficient this would be. You would figure the increased radiating area would make up for inefficient feed from the mismatch.
Then again, using ladder line would tend to make up for that.
73
Then again, using ladder line would tend to make up for that.
73
BJ radionut
Supporting Member and 6m addict
Works great with twin-lead(300/450 Ohm line) and good balanced tuner or good wide-range tuner with 1:1 or 4:1 balun...
BJ radionut
Supporting Member and 6m addict
Coax feedlne
I have my choke right below the balun. And I’m about convinced my mfj balun is goofy. I’ll have new cores tomorrow and just wind my own.
I did a CR dipole once. Build a dipole for the lowest band, then, for your next lowest band, hang a half-wave wire 4" under the first dipole (no connection at feed point). Then, for the next lowest band, hang another element 4" under the previous wire and so on. Only the longest (lowest band) is connected to the coax.
would that be considered a capacitance or inductance antenna? how well did it work?
Unless you're going to use band traps, you will immediately run into a problem when you use the antenna on 80M, while on 160M your center-fed dipole is at a current loop, on 80M, each leg is now a 1/2 wavelength, and you are feeding each element at a high impedance point, eg., a voltage loop. So you go from having a feed-point impedance of less than 50 Ohms on 160M, to a feedpoint impedance of a few thousand Ohms on 80M, and every even harmonic thereof.
If you're not using traps, and you want decent multi-band capability, you should be designing an off-center-fed (OFC) antenna, and in one design, you could calculate the feedpoint impedance to be 450 Ohms, and use a 9:1 UnUn (because now, being an OFC, your dipole is unbalanced) with your 50 Ohms coax to feed the antenna.
How does this solve the problem of low impedance feedpoint on one band and a high impedance on another band? Now that you are OFC, the impedance of each leg of your dipole goes from high on one side to low on the other in one band, and swaps to high and low on other bands, making the total impedance around 450 Ohms.
Personally, I'd do an Inverted-L, calculate the total length of the wire to be a 1/2 wave of 160M, and OCF it at about 12 feet from the end. Using a 25:1 UnUn, and a tuner, and you'll need only two skyhooks to put up the antenna. If you make up a reel, and use about 50 feet of flat copper strap, and put pulleys on your skyhooks, and counter weight the end of your antenna, you can make your antenna tunable and resonant on everything from 160M through 6M, and not need a tuner....and if you're mechanically creative, you can motorize your reel and tune your antenna remotely!
80m is always tricky with a 160m dipole - but it's not impossible. The "all-band" antenna I use the most (SSB & digital at near FLL) is a 160m dipole.
Disclaimer: I am a fan of 600-Ohm 'ladder line'.
I would suggest looking into the merits of replacing your coax with 600-Ohm feedline. There are fundamental differences between the two that are worth understanding, and many advantages with open line. I believe the most important advantage is the low loss tolerance to high SWR - which means you can ignore high SWR in the feedline (where coax crashes and burns) and only worry about SWR at the transmitter (where your tuner can correct it). KD8NPB shows the loss differential nicely in this post. If you have a balanced line tuner it's a piece of cake. If not, then you need a decent 1:1 current balun with a very short coax to the tuner. KV5R has a great set of tutorials on Ladder Line which I have found invaluable.
Good luck !
Disclaimer: I am a fan of 600-Ohm 'ladder line'.
I would suggest looking into the merits of replacing your coax with 600-Ohm feedline. There are fundamental differences between the two that are worth understanding, and many advantages with open line. I believe the most important advantage is the low loss tolerance to high SWR - which means you can ignore high SWR in the feedline (where coax crashes and burns) and only worry about SWR at the transmitter (where your tuner can correct it). KD8NPB shows the loss differential nicely in this post. If you have a balanced line tuner it's a piece of cake. If not, then you need a decent 1:1 current balun with a very short coax to the tuner. KV5R has a great set of tutorials on Ladder Line which I have found invaluable.
Good luck !
love the disclaimer!
im abandoning the 160 for the moment. not forever, just for today. and maybe today for the next couple months.