We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Empty HF frequency band for emergency coms  (Read 441 times)

Offline OgreVorbis

  • Full Member
  • ***
  • Posts: 141
  • Karma: +0/-0
    • View Profile
    • DosaidSoft
    • Email
Empty HF frequency band for emergency coms
« on: January 17, 2021, 2208 UTC »
First of all, I'm not sure if I'm in the right section, so feel free to move this.

OK, so I am preparing for a societal collapse :P I purchased some HF ham radio transceivers. I am on my way to getting my license, however, I will need to use this as a means of communication for some people without licenses.

Assuming the system had collapsed, what HF frequency range should I plan to use that doesn't contain any military or other communications currently? Is there an empty range you could give me? A no mans land. I'm looking for something in the range 3.5 - 10 MHz cause I need to cover a 100 mile distance. My calculations show that 5 - 6 MHz would be the best choice also taking into account those people's lot size. Don't tell me just use ham anyway cause it'll be jammed.

Of course there's the pirate frequencies, but a range is something I'm looking for, not a specific frequency.

Understand that this is only to be used during emergency, so I just want to make sure I'm not interfering with anyone.

Thanks :)
Radio and Programming Blog: http://dosaidsoft.com/wp/

Offline redhat

  • DX Legend
  • ******
  • Posts: 1431
  • Karma: +35/-4
  • USA
  • Music is my drug.
    • View Profile
    • Email
Re: Empty HF frequency band for emergency coms
« Reply #1 on: January 17, 2021, 2332 UTC »
Making any sort of recommendation based on the current condition of frequency usage for an emergency is relatively pointless.  During such an event, band usage is going to be MUCH higher, and what is vacant today likely will be awash in various modes of data and voice.  This is also dependent on whether you are planning for near term, or in the future when propagation likely isn't known.  The best you could do is prearrange some 'calling' frequencies and times to try them, best spread over several band segments to allow for some variation in propagation, time of day, etc.  I would also include alternates located close by in case the channel you want to use is in use.

The simple solution to all these problems is ALE  ;D

+-RH
Somewhere under the stars...
WinRadio Excalibur, Airspy HF+, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline OgreVorbis

  • Full Member
  • ***
  • Posts: 141
  • Karma: +0/-0
    • View Profile
    • DosaidSoft
    • Email
Re: Empty HF frequency band for emergency coms
« Reply #2 on: January 18, 2021, 0736 UTC »
Making any sort of recommendation based on the current condition of frequency usage for an emergency is relatively pointless.  During such an event, band usage is going to be MUCH higher, and what is vacant today likely will be awash in various modes of data and voice.  This is also dependent on whether you are planning for near term, or in the future when propagation likely isn't known.  The best you could do is prearrange some 'calling' frequencies and times to try them, best spread over several band segments to allow for some variation in propagation, time of day, etc.  I would also include alternates located close by in case the channel you want to use is in use.

The simple solution to all these problems is ALE  ;D

+-RH

You're probably right.
I have one more quick question. So I already have my HF broadcast transmitter and an SDR. I was wondering if I could get one of these RF switches as a quick and dirty solution so I don't need an actual transceiver on my end.
https://www.ebay.com/itm/DAIWA-CS-201A-2-Port-Coax-Switch-w-SO-239-UHF-Female-Connectors-Handles-1-5kW/111802127942

It has 60db isolation. Meaning at 1600W PEP, it will have 1.5mW going into the SDR. Is that good enough?
I know it's junky, but I'm unable to find something better. Don't want to spend a lot cause I might not use it.

Thanks.
Radio and Programming Blog: http://dosaidsoft.com/wp/

Offline Stretchyman

  • Hero Member
  • *****
  • Posts: 534
  • Karma: +24/-46
    • View Profile
Re: Empty HF frequency band for emergency coms
« Reply #3 on: January 18, 2021, 0859 UTC »
You'll want to use an RF relay and a method of switching it over when you transmit. Probably a lot easier to buy a transceiver!

Re frequency usage the military have access to the whole of the HF spectrum and far beyond obviously and in times of trouble they'd have access to everything and probably block huge chunks of spectrum along with extensive monitoring.

Btw if you think there are 'unused' parts of the spectrum, there isn't, it's full up!

Regards.

Stretchy.
'It's better to give than receive' so why RX when you can TX!

         15W and100W models available.

                   Buy one from me, NOW!


                                              ;)

Offline ThaDood

  • Hero Member
  • *****
  • Posts: 668
  • Karma: +10/-2
  • Likely, not where you are.
    • View Profile
    • Extreme Part #15!
    • Email
Re: Empty HF frequency band for emergency coms
« Reply #4 on: January 18, 2021, 1827 UTC »
Practically, very little activity is in the 11M International Broadcast Band, 25.670MHz - 26.100MHz. Modify a CB antenna, or just put up a dipole, as high as possible. You'll hear CB outbanders in there during "E" openings, but for the most part, it's empty space, except some broadcast NBFM Auxiliary Stations still out there, but their numbers are dwindling more each year. If you are on a hill, or can put up an 11M Vertical up as high as possible, 100 miles can be had, day, or night. Especially, with a beam antenna. Another bands that's open-wide, with little activity, is the 15M International Broadcast Band, 18.900MHz - 19.020MHz. Also, it wouldn't be tough to retune a 20M antenna for the 22M Band,  13.570MHz - 13.870MHz, (Although, pirates have used 13.900MHz with success a few times.) Just below that, the Part #15 ISM band, (Centered at 13.560MHz.), covers a few miles with just a couple of milliwatts. Anyway... There's lots of little used upper HF spectrum right now, so you can almost take your pick, just don't step on military COMM's.   http://www.hamuniverse.com/shortwavebandfreqs.html
When asked about White Supremacy, I do not believe in it, since most white people that I know are very much mediocre. Therefore, I believe in White Mediocracy.

Offline redhat

  • DX Legend
  • ******
  • Posts: 1431
  • Karma: +35/-4
  • USA
  • Music is my drug.
    • View Profile
    • Email
Re: Empty HF frequency band for emergency coms
« Reply #5 on: January 18, 2021, 1838 UTC »
For a transmit relay, you can use an ordinary DPDT relay.  It would be wise to short the receiver output to ground during transmit.

+-RH
Somewhere under the stars...
WinRadio Excalibur, Airspy HF+, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline OgreVorbis

  • Full Member
  • ***
  • Posts: 141
  • Karma: +0/-0
    • View Profile
    • DosaidSoft
    • Email
Re: Empty HF frequency band for emergency coms
« Reply #6 on: January 18, 2021, 1849 UTC »
Well, I think I'd manually need to trigger it anyway, so I figured that switch would be good enough for me. I won't forget it. If I used a relay, I'd need a delay circuit to another relay to PTT the transmitter and make sure the RF relay had already been opened. I guess it may work triggering at the same time, but that worries me a little. I'll look into that though.
Certainly easier to get another transceiver, but it's a shame I already have a high power transmitter that would work fine.

I checked my SDR datasheet and they say it has a max input of 10dBm, so I think it will be fine with the RF switch. I'll probably just get the switch as a backup and see what I can do with a relay.

Practically, very little activity is in the 11M International Broadcast Band, 25.670MHz - 26.100MHz. Modify a CB antenna, or just put up a dipole, as high as possible. You'll hear CB outbanders in there during "E" openings, but for the most part, it's empty space, except some broadcast NBFM Auxiliary Stations still out there, but their numbers are dwindling more each year. If you are on a hill, or can put up an 11M Vertical up as high as possible, 100 miles can be had, day, or night.

Well, I'm in the least optimal area for those higher frequency bands. I'm in a deep bowl. I figure my only way there is using the ionosphere. How reliable is skywave propagation on those bands? I've never used them. Only done VHF and lower HF and VHF is completely out of the question.
Radio and Programming Blog: http://dosaidsoft.com/wp/

Offline Stretchyman

  • Hero Member
  • *****
  • Posts: 534
  • Karma: +24/-46
    • View Profile
Re: Empty HF frequency band for emergency coms
« Reply #7 on: January 18, 2021, 2004 UTC »
NVIS during the day. 3 to 7MHz.

Keep an eye on MUF on your local ionosonde.

Very reliable and what pirates and the military have used for years.

Forget CB frequencies, useless unless there's sunspots!

Are you one of those prepping types?

Str.
« Last Edit: January 18, 2021, 2009 UTC by Stretchyman »
'It's better to give than receive' so why RX when you can TX!

         15W and100W models available.

                   Buy one from me, NOW!


                                              ;)

Offline BoomboxDX

  • Hero Member
  • *****
  • Posts: 716
  • Karma: +5/-0
    • View Profile
Re: Empty HF frequency band for emergency coms
« Reply #8 on: January 19, 2021, 0410 UTC »
If society collapses, just choose a usable frequency and a time to communicate with others beforehand, and probably it would be best to keep such transmissions short, should the TEOTWAWKI events take place. Not to protect yourself from authorities, who will undoubtedly be preoccupied with trying to hold together, but from potential marauders.

I doubt the military will be taking any measures against individuals using HF spectrum, they will have enough other problems to deal with aside from a few survivalists. CB would be handy in short range comms, as the equipment is portable, easy to use, and still plentiful.

And yeah, the spectrum is all 'spoken for', but in reality much of it is empty. The frequencies surrounding the CB band have been assigned to various governmental agencies for as long as I can remember and yet I have never in my life heard anything on those frequencies that remotely resembles a government agency transmission. Just outbanders.
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline DeepBlue

  • Newbie
  • *
  • Posts: 6
  • Karma: +2/-0
  • No matter where you go, there you are.
    • View Profile
Re: Empty HF frequency band for emergency coms
« Reply #9 on: January 19, 2021, 0457 UTC »
Consider too, do you want your coms monitored by just anyone or are we talking to a specific station?  If you want coms that don't need to be secured for some reason, Amateur bands will be full of voices that may be able to help out in a given situation, depending on the type of emergency that is.  OpSec however is a major concern if you want to live a quiet undisturbed life after a major societal issue.  Listening will yield truths.  Why they never paid more attention to HF radio coms in Walking Dead in the early seasons is totally beyond me.

I have often said that just hearing a transmission is information on it's own level.  Hearing a lot of traffic means one thing, hearing routine traffic is another.  Hearing unwanted visitors on VHF means Danger Close while a fading HF signal is not likely a threat.  Stuff to learn.

Personally I doubt we are on the brink just yet.  I do always suggest people do what our great grandparents did and just be prepared to be on your own for a while, if nothing else in case of natural disaster or say some nasty virus keeps us all on lock down.  I hear the Left Coast had a quake just the other day.  "Learn to Swim" - Tool

My 2 pennies worth,
DB, out.
1001001 SOS
1001001 in Distress

--------------------------------------------------
Receivers: Icom IC-R71A, SDRPlay 2 Pro, IC-R30,  IC-7300, 1937 Philco Tombstone (rebuilt by me)
Antennas: RF Systems DX-10 Pro active, 6BTV

Offline OgreVorbis

  • Full Member
  • ***
  • Posts: 141
  • Karma: +0/-0
    • View Profile
    • DosaidSoft
    • Email
Re: Empty HF frequency band for emergency coms
« Reply #10 on: January 19, 2021, 2130 UTC »
NVIS during the day. 3 to 7MHz.

Keep an eye on MUF on your local ionosonde.

Very reliable and what pirates and the military have used for years.

Forget CB frequencies, useless unless there's sunspots!

Are you one of those prepping types?

Str.

OK, makes sense. I wasn't a prepping type until recently. You're in the UK, so it probably doesn't seem as important there.

Consider too, do you want your coms monitored by just anyone or are we talking to a specific station?  If you want coms that don't need to be secured for some reason, Amateur bands will be full of voices that may be able to help out in a given situation, depending on the type of emergency that is.  OpSec however is a major concern if you want to live a quiet undisturbed life after a major societal issue.  Listening will yield truths.  Why they never paid more attention to HF radio coms in Walking Dead in the early seasons is totally beyond me.

I have often said that just hearing a transmission is information on it's own level.  Hearing a lot of traffic means one thing, hearing routine traffic is another.  Hearing unwanted visitors on VHF means Danger Close while a fading HF signal is not likely a threat.  Stuff to learn.

Personally I doubt we are on the brink just yet.  I do always suggest people do what our great grandparents did and just be prepared to be on your own for a while, if nothing else in case of natural disaster or say some nasty virus keeps us all on lock down.  I hear the Left Coast had a quake just the other day.  "Learn to Swim" - Tool

My 2 pennies worth,
DB, out.

I'd mostly just be talking with another couple stations, but I wouldn't mind if people were listening for the most part. They probably didn't pay more attention to HF because most novices or random people that get ahold of a "ham radio" use a VHF radio. For some reason it's become like the defacto standard even though HF is probably more useful. Like it was pretty hard for me to find cheap HF radios. Almost all of the cheaper ham radios are VHF and I think that's probably what most "preppers" would get. I don't think they bother to think about it any deeper.

Well, maybe not elsewhere in the world, but in the US, something is definitely brewing. Civil war is inevitable in this country.

And yeah, the spectrum is all 'spoken for', but in reality much of it is empty. The frequencies surrounding the CB band have been assigned to various governmental agencies for as long as I can remember and yet I have never in my life heard anything on those frequencies that remotely resembles a government agency transmission. Just outbanders.

Yeah, it does seem like that. It's like everyone is packed into these small bands with emptiness all around. They should have expanded the ham bands. I noticed a couple times that there are licensed HF broadcast stations that are actually outside the allotted bands. Maybe the govt doesn't really care so much about these frequencies cause you would never see that elsewhere. I find it strange they don't seem more interested in these frequencies considering they have good properties that no other bands have.

I guess what I get out of this is - just use whatever as long as it's empty haha.
Radio and Programming Blog: http://dosaidsoft.com/wp/

Offline Kingbear Radio

  • Jr. Member
  • **
  • Posts: 47
  • Karma: +1/-1
  • Universe
  • Kingbear Radio
    • View Profile
Re: Empty HF frequency band for emergency coms
« Reply #11 on: January 21, 2021, 0236 UTC »
I can see that problem with the sensitive RF front end in an SDR, and switching over to a nearby transmitter, it does have to be done with caution.

It was the same thing when IGFETs came out, and they were built into RF preamps. In the circuit they were tougher, but they were still getting blown out at ham stations due to lightning or strong transmissions nearby, and IGFETs were expensive at first.

One thing that was done was to use back to back high speed silicon diodes, like IN914 from antenna input to ground, and a smaller coupling capacitor from the antenna. The diodes conduct first, keeping the voltage clamped down so the RF stage doesn't get enough to harm it.

You could look up diode protection for RF front ends and diode T/R switching in a transceiver for ideas.
K-Bear Radio