So you want to try your hand at a vertical, but have no space or desire to lay down ground radials. Solution: put them up top!
Who this is for:
The beginning swl'er (or amateur even), who has the classic beginner's simple shortwave antenna: a length of coax, where the center conductor is attached to a length of wire at the end and you've strung it up horizontally or even randomly.
Purpose: you'd like to try your hand at a vertical antenna, but you just don't have the room to be laying down wires all over the ground as in a classic vertical construction.
An old trick: we are going to basically turn things upside down and inside out electrically and still have it work. But it needs to be controlled. Used on ships and other areas where a vertical is needed, but no radials are possible down low.
Without getting too specific about lengths, we'll jump right in and scale the lengths later.
1) You hung up 20 feet of wire horizontally.
2) At the end of this wire is your coax running down vertically into your room. If you look carefully, only the center conductor is attached to the end of the wire and of course the other part of the coax goes into your radio.
In this instance, the braid is actually part of your antenna too, not just the horizontal wire. And being run into your room inside, you may be subject to having local noise generators being received by not only the horizontal wire itself, but also by the braid of the coax.
3) Modify the existing antenna by attaching 20 more feet of wire to the existing horizontal and hang it horizontally too.
4) Now you have your coax' center conductor attached to what is the very center of a 40 foot piece of wire, rather than at the end.
Now, in this configuration, these are your vertical radials, only they are up top! That is like having two 20 foot radials opposing each other from the center of the wire to the center wire of your coax. BUT we are doing this backwards! Usually radials on the ground are attached to the braid. Here, we are backwards and the radials are in the air and attached to the center conductor!
Backwards, forwards, upside down! This long wire attached in the center, or two back-to-back radials if you will, do NOT do any of the receiving work. Currents in a wire which are opposite and equal, cancel. These "radials" are merely capacitors to the earth below to allow the antenna to work well.
5) But what about the actual vertical part which is going to do the receiving? The outside skin of the braid is it. But it needs to be *controlled*. We purposely "choke" part of it off. With your coax coming down 20 feet, this is where we'll put a CMC, or common-mode-choke.
There are many examples of 1:1 common-mode-chokes. In the wild you'll see so-called "ugly-baluns", but they are limited in frequency range, not as effective as they could be, and for our purposes, a waste of coax. A better more effective choice is to use FERRITE material to do the choking. One very common example is the MFJ 915 inline choke. There are many articles and options for ferrite choking at HF frequencies other than the MFJ, but this was chosen for common convenience. The moral here is to avoid using "ugly-baluns".
6) On the other side of the common-mode-choke, we run your feedline through the window and into the room to your radio.
That's it!
Q: What if I can't hang 40 feet of wire horizontally, and my only choice would be to bend it. Is that ok?
A: Yes, but try not to bend it more than 90 degrees or you will be heading back towards square one. The horizontal "radials" will start to receive a little bit because it is no long perfectly inline "equal and opposite" as above. But it is not a show-stopper for our purposes. I could imagine these being used at the edge of a house for example. But the larger the angle you can make it to being in a straight line is better.
Q: Can I "broadband" it?
A: Yes. You can place a 4:1 "UN-UN" at the end of the coax and attach a little pigtail from the antenna side of the unun to the very center of your horizontal wire. Don't attach anything to a ground terminal if you have it. The coax, which is doing the receiving, is already attached to the un-un ground, and down near the ground, you have it "choked off" with your ferrite choke.
A commercial example of this would be the LDG RU-4:1 UN-UN. Do not confuse with the similar looking 4:1 balun. Not meant for outdoor use, you'd have to carefully enclose it. Again, this is just used as an example.
Q: Do the lengths have to be totally exact? Not really super-critical for our rx-only purposes, and especially with the 4:1 Un-un should you decide to use it. Ideally though, try to keep your horizontal top wire attachment to either your coax or your 4:1 unun centered.
So there you go. Sure, a vertical *may* be noisy at your location. But you'll never know until you try. If you have a portable shortwave receiver, especially one with ssb, (even if you aren't really interested in that), walk around the property with the antenna held vertically, and see if one location is less noisy than another.
It looks like a lot to read, but in practice, hanging another piece of wire off the end of the simple shortwave antenna kit, and adding a common mode ferrite choke at the bottom could be the start of something very new.
Who this is for:
The beginning swl'er (or amateur even), who has the classic beginner's simple shortwave antenna: a length of coax, where the center conductor is attached to a length of wire at the end and you've strung it up horizontally or even randomly.
Purpose: you'd like to try your hand at a vertical antenna, but you just don't have the room to be laying down wires all over the ground as in a classic vertical construction.
An old trick: we are going to basically turn things upside down and inside out electrically and still have it work. But it needs to be controlled. Used on ships and other areas where a vertical is needed, but no radials are possible down low.
Without getting too specific about lengths, we'll jump right in and scale the lengths later.
1) You hung up 20 feet of wire horizontally.
2) At the end of this wire is your coax running down vertically into your room. If you look carefully, only the center conductor is attached to the end of the wire and of course the other part of the coax goes into your radio.
In this instance, the braid is actually part of your antenna too, not just the horizontal wire. And being run into your room inside, you may be subject to having local noise generators being received by not only the horizontal wire itself, but also by the braid of the coax.
3) Modify the existing antenna by attaching 20 more feet of wire to the existing horizontal and hang it horizontally too.
4) Now you have your coax' center conductor attached to what is the very center of a 40 foot piece of wire, rather than at the end.
Now, in this configuration, these are your vertical radials, only they are up top! That is like having two 20 foot radials opposing each other from the center of the wire to the center wire of your coax. BUT we are doing this backwards! Usually radials on the ground are attached to the braid. Here, we are backwards and the radials are in the air and attached to the center conductor!
Backwards, forwards, upside down! This long wire attached in the center, or two back-to-back radials if you will, do NOT do any of the receiving work. Currents in a wire which are opposite and equal, cancel. These "radials" are merely capacitors to the earth below to allow the antenna to work well.
5) But what about the actual vertical part which is going to do the receiving? The outside skin of the braid is it. But it needs to be *controlled*. We purposely "choke" part of it off. With your coax coming down 20 feet, this is where we'll put a CMC, or common-mode-choke.
There are many examples of 1:1 common-mode-chokes. In the wild you'll see so-called "ugly-baluns", but they are limited in frequency range, not as effective as they could be, and for our purposes, a waste of coax. A better more effective choice is to use FERRITE material to do the choking. One very common example is the MFJ 915 inline choke. There are many articles and options for ferrite choking at HF frequencies other than the MFJ, but this was chosen for common convenience. The moral here is to avoid using "ugly-baluns".
6) On the other side of the common-mode-choke, we run your feedline through the window and into the room to your radio.
That's it!
Q: What if I can't hang 40 feet of wire horizontally, and my only choice would be to bend it. Is that ok?
A: Yes, but try not to bend it more than 90 degrees or you will be heading back towards square one. The horizontal "radials" will start to receive a little bit because it is no long perfectly inline "equal and opposite" as above. But it is not a show-stopper for our purposes. I could imagine these being used at the edge of a house for example. But the larger the angle you can make it to being in a straight line is better.
Q: Can I "broadband" it?
A: Yes. You can place a 4:1 "UN-UN" at the end of the coax and attach a little pigtail from the antenna side of the unun to the very center of your horizontal wire. Don't attach anything to a ground terminal if you have it. The coax, which is doing the receiving, is already attached to the un-un ground, and down near the ground, you have it "choked off" with your ferrite choke.
A commercial example of this would be the LDG RU-4:1 UN-UN. Do not confuse with the similar looking 4:1 balun. Not meant for outdoor use, you'd have to carefully enclose it. Again, this is just used as an example.
Q: Do the lengths have to be totally exact? Not really super-critical for our rx-only purposes, and especially with the 4:1 Un-un should you decide to use it. Ideally though, try to keep your horizontal top wire attachment to either your coax or your 4:1 unun centered.
So there you go. Sure, a vertical *may* be noisy at your location. But you'll never know until you try. If you have a portable shortwave receiver, especially one with ssb, (even if you aren't really interested in that), walk around the property with the antenna held vertically, and see if one location is less noisy than another.
It looks like a lot to read, but in practice, hanging another piece of wire off the end of the simple shortwave antenna kit, and adding a common mode ferrite choke at the bottom could be the start of something very new.
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