HF Basics for TEOTWAWKI Long Distance Communications

HF Basics for TEOTWAWKI Long Distance Communications

We have previously talked about VHF/UHF  FM mode, CB, FRS/GMRS/MURS for local communications.  Now I would like to talk about the real meat and potatoes of Ham Radio.  This is the stuff that made Ham Radio, HF or High Frequency.  To set the stage, let’s review a few things about bands, frequencies and frequency allocations.  Traditionally back in the day when radio was about the only choice for entertainment and communications; before television and of course, way before the internet, the commercial bands were simply LF (long wave) low frequency AM mode….primarily used by the police and public service people. MW (medium wave) primarily used by local and national superstations in AM mode for commercial radio broadcasts.  Even today we still traditionally use this MW band for our commercial AM radio stations.  The range from this band is 540 Kilohertz (KHz) to the high end 1700 KHz.  There were no FM radio modes at that time.  Now the SW or Short Wave band was used for intercontinental commercial radio, and other very long distance AM communications.

The SW bands are what we will be talking about now…but we refer to them now as High Frequency bands because VHF and UHF were not available then, and are now.  So, kind of an enigma HF is actually the lowest frequency used by Ham Radio operators.  HF is located from 1800 KHz or more plainly 1.8 Megahertz (MHz).  As you can see, this is directly above the MW or what we call now the Broadcast Band.  Police and other public service frequencies have moved up to the VHF and higher bands.

Now you know about where on the frequency allocation chart the VHF band sits.  The lowest frequency band is called the 160 meter band.  It is a very narrow band, and because it requires a very long antenna…a full wave would be about 480 feet long.  It is used when the other bands are not available because of static problems or solar storms.  Most of the people who use this band are the more experienced hams.  It is usually not as crowded as the 75-80 meter band.  Many of the linear amplifiers do not have the circuitry to accommodate this band.

This is a good time to understand a little about ‘SKIP”.  The thing that makes HAM radio so important for long distance communications is its ability to bounce off of the ionosphere.  We talked about the ionosphere before when we were talking about CB radio and VHF FM radio.  When the sun is shining on the part of the earth where it is day time, the ionosphere thickens up and reflects or absorbs much of the radiation that comes from the sun.  This is part of the reason that we can live on the earth.  As a consequence when lower frequency radiation hits the ionosphere it also bounces, but it bounces back to the earth.  When the sun is not directly shining on the part of the earth where it is night time, the ionosphere thins out, and increases its distance from the earth.  Now then lower frequency radiation hits, it bounces back but the distances between the origin and reception point is much larger since the Ionosphere is further from the earth.  Now, the problem is to keep the frequency low enough to bounce it off of the ionosphere.  If it is too high, it will pierce the ionosphere.  We find this frequency by actually using technology, and then reporting it back under the name MUF, or what we call the Maximum Usable Frequency.  So if the frequency is below this MUF, you can be assured that you will be able to utilize the SKIP for long distance communications.

Along with the ionosphere bouncing radio waves back to the earth, we can see that during the day, when the ionosphere is thicker and lower, one can use higher frequencies, and conversely during the evening hours the higher frequencies will be higher than the MUF and proceed out into space. So we have to use lower frequencies to bounce back to earth.

The evening and night bands are the lower bands.  The 160, 80-75 and 40 meter bands are the usual one’s that we use for comms at that time.  So, when you set your schedules to talk to your family you must consider that the best time to do this is in the early morning or evening, and using the 75-80 meter band.  During the day the 40 and 20 meter bands are the best for daytime communications. 

I don’t intend this to be a primer on getting a HAM license, nor a class on HAM radio.  What my intentions are is to address some of the general questions people have about HF radio.  If you want the frequencies, and the intricacies of operation, better get the books and or the classes offered by your local HAM club.

Let’s talk about some radios.

The older sets which were used in the 40’s-60’s were all basically run by using vacuum tubes in place of transistors.  They are heavy, and they are very reliable especially during an EMP threat.  Since they have no integrated circuits or transistors in them, they are not subject to EMP.  But they are quite heavy and bulky and are pretty much impossible to move easily from one location to another.  They are also pretty pricy now because they are collector’s items.  Some call them “boat anchors” because they are so heavy and bulky.  About the only way you will find these is if you happen on one that is working, on eBay.  However, many are still running, and the tubes can be found somewhat readily in the HAM community.  You do need to be handy with electronic maintenance because they do require regular work.

At the onset of transistors in the 60’s and the 70’s Kenwood started making hybrids.  That is, using transistors for the receiver section or the front end, and then using vacuum tubes in the transmitter.  This was the first transceiver type radio, since many of the original radios were either transmitters OR receivers and not both.  This hybrid gave the owner a large advantage in size reduction, and the tubes still allowed a significant amount of power to be used in the transmit stage.  At the present time, HAM radios are quite small, and with the onset of IC’s (integrated circuits) are very handy to carry about in either mobile or base station use. 

Most HF radios run at top end wattage of 100 to 200 watts, no matter the physical size.  The amperage in the duty cycle runs around 20 to 30 amps, so they do use a significant amount of power in the transmit stage, and can run a battery down quite quickly.  Therefore it is smart to have an array of batteries do draw from if you plan on talking a lot.  There is also a device called a linear amplifier that can be used to boost power to 1500 watts, legally pre-TEOTWAWKI, and post TEOTWAWKI the sky is the limit.  But as with all good things, remember that the more you talk, and the stronger your signal the easier it is to find you.  The good thing about HF radios is that once the first skip or bounce occurs, it becomes impossible to find a station by direction finding equipment.  However the ground wave or the local emission is easily found by the bad guys using a loop antenna.  So be advised.  Also as to effectiveness the rule of thumb is that by doubling your poser, you gain one “S” unit.  So if you are broadcasting at 100 watts, to gain 1 S-unit you will have to increase to 200 watts.  If you want to move up 2 S-units you have to double the power again to 400 watts.  If you want to move up 3 S-units you have to double to 800 watts.  So there is a cost-loss issue here; Power is not always the answer as we shall discuss next.  I have personally spoken with a gentleman over 360 miles from my home who was using a 1 (one) watt station, and could carry on a great conversation (QSO).  I on the other hand had to use over 400 watts to get back to him.  Why?  Simply all in the antenna.

Antennas

Since this in not a class on radio, and just a primer I will not go in detail as to antennas and types, lengths, materials and such only an overview of types.  Even the overview will be an overview!  If you want to go into detail and help to actually make antennas you will have to contact me for a class, or check other sites for different plans because nearly every HAM will have a particular type of antenna that they think is better than all of the rest.

The most simple antenna is a just a wire.  This works especially well for receiver antennas as is usually called a “beverage” antenna.  If you use it for a transmission antenna you will have to have an antenna tuner to make it compatible with your transmitter and frequency.  But if you are just trying to hear transmissions from all over the world, this antenna works fine.  It is a wire strung up from the radio to another high point, the longer the better.

The easiest antenna to use for transceiver work is the common Dipole.  It is a length of wire, usually ½ wavelength long with a feed line hooked to the center of the antenna.  For example in the case of 40 meters, it would be a total of 60 feet long, and the center of the antenna would be around 30 feet.  So, the dipole would be 30 feet long approximately on either side of the center.  One side of the antenna would attach to the shield of the coax feed line if you are using coax to hook up, and the other side would go to the center of the coax feed line.  Attach to your HF radio tuner, and then to the actual radio itself, and you are ready to go on the air.  The only other thing would be to make sure you have a ground rod in place, and it reaches to the moist part of the dirt at all times.  If you don’t have access to damp soil you will have to make it damp yourself however you do that is up to you.

Unless you have access to an antenna analyzer and can cut the antenna to the correct length for the band you are using, you will have to use an antenna tuner, or be able to make the mathematical calculations necessary to cut the antenna length to the right size.  Basically though you can take the band name, for example the 160 meter band 160 meters is the full length of the antenna, ½ wave antenna would be 80 meters, which would be a full wave length of an 80 meter antenna and so on.  Radio waves have harmonics that can be tuned in equal multiples.  Therefore a ¼ wave antenna for a 160 meter band is the same as a full wave for a 40 meter antenna.  This is basically the fun part of the radio work.  But simply purchasing an antenna tuner works for all of theses different bands, and fools the radio into thinking that it is feeding an actual tuned and cut antenna.

To summarize then, with a tuner, you can use a ½ wave 80 meter antenna for a 40 meter radio. The advantage to this is that your full wave 40 meter antenna which is 120 feet long approximately can be made into a dipole of 60 feet on each side and you have a very efficient antenna for both bands; one daytime band, and one nighttime band in the same antenna.  You can also use this same antenna for 20 meters, another good daytime band.

Dipoles are pretty much Omni-directional unless you have them mounted over one wavelength high.  Then if you do have them 120 feet high you will find that they are directional broadside to the antenna, and the null will be on the end of the antenna.  If it is less than one wave length high at the peak, the antenna will radiate 360 equally.  The higher the antenna is, the lower the take off angle and the better skip you will get: Which means the further you will talk.  Conversely the lower the antenna is to the ground, the higher the takeoff angle is, which means that a few feet above the ground, and you will have what is called a cloud-burner, and this means that your skip will not be as efficient and hence you will not have very far skip, or the efficiency of the antenna will be greatly diminished.  Which may be a good thing…?

NVIS (Near Vertical Incident…) is a type of antenna used by the military to talk within the skip hole, so that you can talk within the approximately 300-400 mile doughnut hole.  We have used this type of antenna quite a bit in some of the organizations that I have been associated with, and the AS2259 military model of this type of antenna is also harmonic on the 2 meter band for greater power and coverage in that band.  However you do have to cut the antenna back from the military specs because they use frequencies a little higher than the HAM band 80 meters.  Verticals should be mounted on the rear bumper and then stretched forward to the front of the vehicle so that it is in a horizontal position.  In this position it can be used as an NVIS antenna in mobile mode.