Forwarded from Doomsday Tradecraft
How do you make a wire antenna directional?
A plain long wire talks in two directions at once — forward to whoever you're working, and backward to everyone behind you. You can't rotate it and you can't switch off the back lobe. But you can absorb it.
Here's why it happens. Power runs up the wire, reaches the open far end, and has nowhere to go, so it reflects and travels back — radiating the whole way. That returning wave is the rear lobe.
The fix is a resistor. Connect the far end to ground through a 500 to 600 ohm non-inductive resistor. The forward wave still radiates all the way down the wire; whatever is left at the end gets absorbed instead of reflected. Nothing travels back, so nothing radiates rearward.
The trade is better than it sounds. On a five-wavelength wire at 14 MHz, terminating cuts rearward radiation by roughly 15 dB and costs about 2 dB forward. Shorter wires pay more — a two-wavelength V-beam gives up around 3.5 dB. And the power heating that resistor is power that would have gone backward anyway.
Component choice matters more than people expect. Wirewound resistors are useless here — the winding behaves as a coil at RF. Carbon types are electrically fine but handle only a few watts, so QRP only. Whatever you use needs a rating of half your transmitter output, short leads, and a weatherproof box at the far end. A useful trick: three resistors in series instead of one reduces stray capacitance.
Build notes: one wire, two wavelengths or longer, 3 to 7 metres up, as straight as the ground allows. Good ground at both ends. Below 12 MHz, point the terminated end straight at the distant station.
Save this for your comms binder.
Send it to someone whose wire antenna hears everything from everywhere.
Full comms course on the profile.
#hamradio #radio #antenna #army #recon
A plain long wire talks in two directions at once — forward to whoever you're working, and backward to everyone behind you. You can't rotate it and you can't switch off the back lobe. But you can absorb it.
Here's why it happens. Power runs up the wire, reaches the open far end, and has nowhere to go, so it reflects and travels back — radiating the whole way. That returning wave is the rear lobe.
The fix is a resistor. Connect the far end to ground through a 500 to 600 ohm non-inductive resistor. The forward wave still radiates all the way down the wire; whatever is left at the end gets absorbed instead of reflected. Nothing travels back, so nothing radiates rearward.
The trade is better than it sounds. On a five-wavelength wire at 14 MHz, terminating cuts rearward radiation by roughly 15 dB and costs about 2 dB forward. Shorter wires pay more — a two-wavelength V-beam gives up around 3.5 dB. And the power heating that resistor is power that would have gone backward anyway.
Component choice matters more than people expect. Wirewound resistors are useless here — the winding behaves as a coil at RF. Carbon types are electrically fine but handle only a few watts, so QRP only. Whatever you use needs a rating of half your transmitter output, short leads, and a weatherproof box at the far end. A useful trick: three resistors in series instead of one reduces stray capacitance.
Build notes: one wire, two wavelengths or longer, 3 to 7 metres up, as straight as the ground allows. Good ground at both ends. Below 12 MHz, point the terminated end straight at the distant station.
Save this for your comms binder.
Send it to someone whose wire antenna hears everything from everywhere.
Full comms course on the profile.
#hamradio #radio #antenna #army #recon
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Forwarded from Doomsday Tradecraft
Should your antenna be vertical or horizontal?
It matters more than most people assume. A radio wave carries an electric field lying in the same plane as the wire that launched it — stand the antenna up and the field stands up too. That orientation travels with the signal, and the receiving antenna only extracts energy lying in its own plane.
Cross the two on a direct path and you can lose up to 20 dB. Same power, same distance, clear path, and most of it never arrives. One exception is worth knowing: skywave comes back from the ionosphere elliptically polarised, so on HF long-haul and NVIS the orientation barely counts. This is a direct-path rule — VHF, UHF and ground wave.
So which one? Height decides. Below about three metres — a whip on a pack or a vehicle — vertical gives the stronger signal, clearly so up to 50 MHz. Get both antennas to ten or twenty metres and horizontal wins instead. Most portable stations never leave the first case.
Vegetation flips it. Trunks and stems act like a screen made of vertical wires, and wet foliage makes that screen conductive — it absorbs vertically polarised signals on contact. Under canopy, lay the wire flat. And keep it clear of leaves entirely, because wet foliage touching the wire grounds the signal out.
One more difference nobody mentions. A vertical whip radiates the same in every direction, which is convenient when you're moving and means everyone within range hears you equally. A horizontal half-wave is bidirectional — it has two ends that radiate almost nothing. That's not a flaw. It's a choice about who gets to hear you.
Save this for your comms binder.
Send it to someone running a vertical under heavy trees.
Full comms course on the profile.
#hamradio #radio #antenna #polarisation #recon
It matters more than most people assume. A radio wave carries an electric field lying in the same plane as the wire that launched it — stand the antenna up and the field stands up too. That orientation travels with the signal, and the receiving antenna only extracts energy lying in its own plane.
Cross the two on a direct path and you can lose up to 20 dB. Same power, same distance, clear path, and most of it never arrives. One exception is worth knowing: skywave comes back from the ionosphere elliptically polarised, so on HF long-haul and NVIS the orientation barely counts. This is a direct-path rule — VHF, UHF and ground wave.
So which one? Height decides. Below about three metres — a whip on a pack or a vehicle — vertical gives the stronger signal, clearly so up to 50 MHz. Get both antennas to ten or twenty metres and horizontal wins instead. Most portable stations never leave the first case.
Vegetation flips it. Trunks and stems act like a screen made of vertical wires, and wet foliage makes that screen conductive — it absorbs vertically polarised signals on contact. Under canopy, lay the wire flat. And keep it clear of leaves entirely, because wet foliage touching the wire grounds the signal out.
One more difference nobody mentions. A vertical whip radiates the same in every direction, which is convenient when you're moving and means everyone within range hears you equally. A horizontal half-wave is bidirectional — it has two ends that radiate almost nothing. That's not a flaw. It's a choice about who gets to hear you.
Save this for your comms binder.
Send it to someone running a vertical under heavy trees.
Full comms course on the profile.
#hamradio #radio #antenna #polarisation #recon
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Forwarded from Doomsday Tradecraft
How long should a radio transmission actually be?
Fifteen seconds. Twenty is the absolute ceiling. Count that out loud sometime — it's barely a sentence and a confirmation, and most operators blow past it before they've finished saying hello.
The reason is mechanical. Direction finding needs your carrier present long enough for a station to take a bearing, and it takes several stations doing that at once before their lines cross into a position. A short over gives them one bearing and nothing to cross it with. You're not hiding the transmission — you're making it too brief to be useful.
There's a checklist for what gets extracted from intercepted traffic, and it has a name worth memorising: SELDOM UP. Strength, Equipment, Logistics, Disposition, Organization, Movement, Units, Personalities. None of it has to be said deliberately to be given away.
Some habits hand it over for free. Tuning and testing on air broadcasts your position with no message attached at all. Chatting between operators builds a pattern of life. Using your own name is the easiest entry point there is. Calling when the net has been silent tells them something just changed.
The fix is unglamorous: write the message out before you key, strip everything that isn't needed, then read it once. The pauses and the corrections are where your twenty seconds actually go.
And a correction to how most people rank this. Encryption is the third line of defence, not the first. Before it come not transmitting at all, and transmitting briefly. If they can't read you, they still know you're there — and they can jam you or come find you instead.
Save this for your comms binder.
Send it to someone whose overs run a full minute.
Full comms course on the profile.
#hamradio #recon #emcomm #opsec #radio
Fifteen seconds. Twenty is the absolute ceiling. Count that out loud sometime — it's barely a sentence and a confirmation, and most operators blow past it before they've finished saying hello.
The reason is mechanical. Direction finding needs your carrier present long enough for a station to take a bearing, and it takes several stations doing that at once before their lines cross into a position. A short over gives them one bearing and nothing to cross it with. You're not hiding the transmission — you're making it too brief to be useful.
There's a checklist for what gets extracted from intercepted traffic, and it has a name worth memorising: SELDOM UP. Strength, Equipment, Logistics, Disposition, Organization, Movement, Units, Personalities. None of it has to be said deliberately to be given away.
Some habits hand it over for free. Tuning and testing on air broadcasts your position with no message attached at all. Chatting between operators builds a pattern of life. Using your own name is the easiest entry point there is. Calling when the net has been silent tells them something just changed.
The fix is unglamorous: write the message out before you key, strip everything that isn't needed, then read it once. The pauses and the corrections are where your twenty seconds actually go.
And a correction to how most people rank this. Encryption is the third line of defence, not the first. Before it come not transmitting at all, and transmitting briefly. If they can't read you, they still know you're there — and they can jam you or come find you instead.
Save this for your comms binder.
Send it to someone whose overs run a full minute.
Full comms course on the profile.
#hamradio #recon #emcomm #opsec #radio
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