Cliff Notes for Radio Communications – A Very Good Link

Provided by Jeff Alan, a reader and frequent comment provider. I am blessed to have many that have a vast knowledge of  radio experience and don’t mind sharing it.

http://www.ar15.com/forums/t_10_22/604477_Ham_Radio_101.html

The article is lengthy, but has a ton of good basic information.

In light of the recent discussions over at Western Rifles regarding, “Get your ham license so you can get some experience under your belt” versus “Who does the government think they are telling us we need a license”, the introduction to the article pretty much explains why the bands are regulated.

CAMP COMMS

Source: CAMP COMMS

HF versus VHF/UHF

Guys, lots of questions coming in regarding HF vs. UHF/VHF radios and antennas. Let’s flog that deceased equine a little longer; If you get your Amateur license at the Technician level, you won’t have to ask these questions any longer.

VHF/UHF radios work on the frequency bands that inherently use short/very short antennas, plus, they are usually very small, light weight, easy to operate, and run off of batteries. What’s not to like! I think this is why most folks initially purchase these radios as inter-squad level comms.

And while they do have those advantages, one of their major disadvantages is that they usually only work when they are in unobstructed view (line-of-sight) of one another. Put most any obstruction between the two (an area known as the First Fresnel Zone) and you have no or very poor comms. The obstruction could be just about anything; a hill/mountain, forest, large buildings, moving vehicles, or any combination of these things. In addition, factors such as power output and receiver sensitivity are also in play.

So, how do we get around (or over) those obstructions? Use a repeater mounted above the obstruction. Then you are relying on someone Else’s infrastructure. And if you do get comms over the mountain to your buddy in the next valley, how do you get to the valley beyond him? Another repeater.

Here is the link for a well put together article on comms for the beginner from INFORMOPS. Take a look toward the end of the article for some visual descriptions of the challenges regarding VHF/UHF comms. I should have had his blog listed as one of my favorites a while back, my mistake. HT to PSYOP Soldier for reminding me.

Comms 101- 2M VHF

Antenna Systems

I am going to attempt to answer several readers comms questions over the next few weeks by giving an explanation of my current HF setup for local to mid distance comms.

I use a digital software, RMS Express (part of the WINMOR package) in conjunction with a certain antenna system, HF transceiver, 12 volt power supply, a PC, tuner and a modem. This setup allows for reliable HF communications from 0 out to about 300 miles, across the wildly varied terrain of the Southern Appalachian mountains and adjoining foothills. This system will pretty much give me coverage in all of the valleys and ridges in my area. Try that with a VHF/UHF system even if you have repeaters. My current setup requires no external infrastructure outside of a 12 volt car battery and a way to keep it charged. I can use my car charging system, home solar system or a man-portable solar system depending on which rig I use; my base station or my tiny man-portable system.

First, you have to have your General or higher Amateur Radio License to access the frequencies you will need to make this work. If you are thinking that you and your buddies will put this system together after SHTF and start talking, then you are delusional. The group I routinely make comms with all hold General and Extra Amateur licenses and it still took about 3 months for us to work the bugs out. If you think that you can pirate the frequencies to test and maintain your system you are even more delusional. The “Ham Nazis” will catch you and turn you over to the FCC. They will look up your bogus call sign on the internet and DF your location just for sport (look up “foxhound”). And rightly so. They took the time and expense to study and pass the test. It’s not that hard. Now that we have again beaten the proverbial dead horse regarding licenses (much like Mosby and PT) lets get on to the equipment.

The antenna I currently use, and have a lot of success with is the Buckmaster 300 watt, 7 band OCF antenna.

http://hamcall.net/7bandocf.html#7band

I chose this antenna for several reasons.

Being a offset center fed (OCF) antenna (45′ on one side, 90 on the other, total of 135′) allowed me to physically locate the feed point of the antenna closer to my radio room with a shorter lead in RG-8 coax, about 30′ long. I had less room to fit the antenna along one side of the building than the other.

The antenna is resonant on nearly every band I use, it always tunes up quickly, doesn’t require a tuner (I still use one) and, if properly installed, has very little VSWR. Some radio guy will me write to say “My such-and-such antenna works better and costs less. Great, send the info. on it. The Buckmaster has worked great for me for years now. Dodge, Chevy, Ford, whatever…..

If you are interested in working down in the 160 meter band (which I am for reasons I won’t go into here) then go for the Buckmaster 8 band antenna. Just remember you will need approximately 270′ of space, or nearly a football field. And, you will most likely need a tuner for 160 meters.

On their website, Buckmaster shows the antenna slung up higher at the mid-point than at the ends. That is correct if you intend to make HF comms like most Ham operators, as long-haul as possible. I, however, want to make comms that will fill in the area between the ground wave and the sky wave. The dreaded “Skip Zone”. If I want to make long-haul comms, I will raise the center rope.

Here is a link that describes the skip zone:   https://en.wikipedia.org/wiki/Skip_zone     Pay particular interest in the words “vertical incident”.

Since most of the folks I want to talk to are in my region (Meat Space Folks) I need a technique that overcomes the skip zone. That technique is Near Vertical Incident Skywave or NVIS.  Yet another link if you have the time:

https://en.wikipedia.org/wiki/Near_vertical_incidence_skywave

Bottom line for me and most of the folks I talk with: we have our antennas generally about 12′ off of the ground for the entire length of the antenna. Once you are on the air, you can adjust it up or down and see what happens.

Some folks will say it is a more efficient use of RF power to build an antenna for the center freq you are using in each band and use a tuner. That is true, however, if you work off of a Signal Operating Instruction (SOI) that says to change your frequency twice a day, every day (60 total for each band per month), then the multi-freq antenna becomes more desirable.

My antenna is attached to trees using Dacron UV resistant ropes that I found at The Wireman. His link:  http://www.thewireman.com/   I attached marine pulleys (also bought at Wireman), to trees at the 2 ends and center points, attached the rope to the end insulators and center balun connector, connect one end of the RG-8 coax to the balun and hosted away. Then I tied the free running ends of the ropes to fence staples at the base of the trees. You can attach strain relief to the ends of the coax for extra security.

In good SF comms tradition, I drilled a hole into the exterior wall of my radio room and fed the coax though it. I still have not foamed the hole shut. I have a friend who would be mortified if he saw my radio room. His looks like the helm of the Star Ship Enterprise. Too each his own, mine is functional, and can be torn down quickly and thrown into a couple of Pelican cases.

Digital HF Transmission Methods vs. IMC

What follows is a belated response to a recent comment regarding Morse burst devices.

Most folks don’t realize that international Morse Code (IMC) is a very early form of binary communications; Dits and Dahs or ones and zeros.

All Amateur (Ham) license holders before 2007 and every Special Forces 18E (Communications NCO) before 2002 were required to learn IMC. Why? Because prior to Satellite communications and the advent of some of the newer software based data transmission methods now available, it was the preferred method of making reliable long haul HF Communications. IMC is more reliable by magnitudes than voice communications across the HF spectrum. It still remains, in my opinion, THE method requiring the least amount of fragile (breakable) equipment. Since the code requirements have been dropped on the civilian side, very few ham operators are willing to invest the time to learn a new language (IMC). In my day, most 18Es could send and receive Morse at 18-5 letter groups-per-minute (GPM) . I knew some that could regularly tap out 24 GPM with a leg key. But comms guys, being the techno geeks they are, were soon experimenting with ways to speed up the method of delivery. More speed meant less chance of intercept and DF. But more importantly, it meant less time someone had to crank that damned G-76 generator.

And in Army SF, why bother with a mode of communication that requires the apparent use of special, secret incantations muttered by the senior comms guy hovering over the AN/PRC-74. He was usually seen conducting this ancient rite while the junior comms guy twirled the appropriate analog knobs and flipped some switches that were labeled on the same heavy green radio in some archaic hieroglyphic script known only our secret sect. It is much easier and faster to throw out that TACSAT antenna, point it at the bird, punch in the freqs, load the fill and talk. So easy in fact, that even an 18B like Mosby could do it….. I digress…. Back to IMC.

One of the first high-speed, low drag code burst devices I had the misfortune of working with was the AN/GRC-81 Coder Burst (took some real imagination to come up with that name, huh). Basically, by doctrine, the Team Commander (in actuality, one of the Echos) encrypted the message on a one-time-pad (OTP), recorded the message onto a tape using what looked like a modern Dyno embossing machine, hooked the device to the transceiver and sent it. The receiving station recorded the message to a tape, played it back and broke it out with the other half of the OTP. It generally sped transmission up to 300 WPM. If you are interested, here is a link: http://www.militaryradio.com/spyradio/gra71.html

Next came the Racal DMDG designated the OA-8990/P (or KY-879/P). The DMDG weighed in at about 9 lbs and had a send/receive rate of about 266.6 baud or 27 characters a second when used with HF.  The message was still encrypted using a one-time-pad (OTP), then was typed into the DMDG using the top mounted keypad and displayed on a then state-of-the-art LCD display. The DMDG was connected to the radio and the message was sent. The receiving station used the same device to record and display the message. Again, it was manually decrypted using the other half of the OTP. A typical 120 group message took about 38 seconds to send or receive. It could also be used with the early AN/PSC-3 Satellite Communications Transceiver. Manual link here: https://books.google.com/books?id=z9UXAAAAYAAJ&pg=0#v=onepage&q&f=false

Finally, we were issued the tiny (by 1980 standards) TRW KL-43. The message was typed into the device using the front mounted keyboard. In most cases we used the eraser end of a lead pencil, since the keys were easy to fat finger. The key was pre-loaded into the device (goodbye OTP!) using the same keypad and could be updated remotely. The KL could be used to send/receive over multiple devices including telephone, satcom and just about any radio transceiver. Transmission rate was about 30 characters-per-second on HF.   http://www.jproc.ca/crypto/kl43.html.

Nowadays, it seems that the majority of SF comms guys could care less about HF comms. Not nearly as sexy as that TACSAT or world-wide computer network. That being the case, you will now find that almost all HF data transmission innovation comes from the civilian amateur radio arena. And I have to say, most of them work as well, and a lot faster than IMC. So let’s look at what’s available.

Rather than list every available program out there, I’ll list a link that provides a fairly detailed description of the most popular:   http://www.hamuniverse.com/hfdigitalmodessoftware.html   A side note: most of these programs require a modem between the computer and the transceiver. Some of these modems are specialized and can be very costly. I have limited my discussion to programs that I have used and that can be interfaced with the Tigertronics Signalink USB. The Signalink can be had at their website for about $120.00 to include the cable for your type of radio.

Which ones do I prefer? Depends on what I’m trying to accomplish.

DigiPan is a pretty good place to start. Easy to install, run and won’t overwhelm a new operator. Don’t expect your messages to have any anonymity if that’s what your after. Everyone on the freq with the program can read what you send. PSK has it’s limitations, but it can be a lot of fun for the beginner. Free.

Airlink Express is DigiPan on steroids. Lots of new features and easy to use if you are familiar with DigiPan. Free-donations accepted if you are happy with it.

RMS Express is probably my favorite. Replicates email on HF/VHF/UHF radio with Peer-to-Peer (P2P) and Bulletin Board Services (BBS).  You can set up your own private network or join several existing networks. Fairly secure comms set up in a nearly bullet proof format. Free, but donations are accepted. Set up with a NVIS antenna and you’ve got your local-to-mid distance network.

The next 2 programs only require a computer with a soundcard and the radio.

IZ8BLY Hellshreiber is an easy to use, very reliable system that works well in noisy conditions. Free, will take donations.

TruTTY – lots of modes, somewhat complicated. $39.00

MultiPSK – The Mother of All Communications softwares. Pretty complicated for the newbie.

Bottom line: IMC will usually get through when voice comm fails due to HFs inherent noisiness. For those who don’t care to learn IMC, a digital program will probably do just as well if not better. However, it’s pretty hard to beat the equipment simplicity of an IMC key.