HF-Radio - Communications During Difficult Times

January 27, 2007
by Bernard

The HF band was the primary frequency range for radio communications over long distances before the age of Tropospheric Scatter and Satellite radio links.

The HF band offers good (but not totally reliable) OTH communications. At its low end (3 to 5 MHz), surface wave (or ground wave) paths are possible, especially at sea. At its high end (9 to 30 MHz), daytime ionospheric paths are possible. At the low-end and up to about 7 MHz, nighttime ionospheric paths are practical. For short to medium ranges, the 5 to 9 MHz range is ideal for tactical use on a 24-hour basis.

The ideal HF radio for survivalist and emergency use is a low-power (up to 25 W PEP) portable or mobile transceiver (transmitter + receiver package), covering the 3 to 15 MHz band (minimum) with CW and SSB mode capability. Both USB and LSB, and possibly AM or AME modes are desirable for voice communications, but USB (or simple AM) would be the minimum requirement.

SSB mode is more power efficient than the old-fashioned AM mode (both sidebands with full carrier) because the power consumed by transmitting the carrier is eliminated and the un-needed other side-band is discarded.

However, the most efficient and simple mode for medium and long-range comms is the CW or radio telegraph (on-off keying) followed by radio teleprinter communications using FSK.

At least one person in each group should be able to send (by hand) and receive (by ear) the international Morse Code and operate a radio in the CW mode.

[It is very easy to build simple CW HF transmitters and transceivers today. A two-transistor transmitter, teamed up with a good HF receiver is an effective way to link survival groups using hand-sent CW mode and/or computer generated RTTY signals. (There is an easy way to frequency-shift key a simple crystal-controlled transmitter, but a FSK demodulator or computer sound-card program is needed to receive the signal.)]

Everyone in the group should become familiar with Directed Net operating format. A directed net, managed by a net control station (NCS) is vital when passing emergency message traffic. This is true even for UHF (FRS band), VHF, and CB band operations.

TRANSMITTER POWER:

I emphasize low- to medium-power operation for several good reasons.
1. High-power transmitters (30 to 100 W PEP) eat batteries. You need to be able to stay on the air for more than a few hours without having to change or recharge the battery.

2. In an age of Big Brother surveillance, a big signal stands out as a "sore thumb target". Strong signals attract unwanted attention. Net communications should take place with tactical call-signs, on pre-arranged frequencies. High-power should never be needed.

NET SECURITY:

Do NOT use Amateur Radio band frequencies. These also will draw unwanted attention. Most Amateur Radio operators are very protective of "their" bands and are committed to adherence to the FCC Rules and Regulations. "Unlicensed" operations on those bands will be noticed and tracked down. Non-Amateur users will be turned-in to the FCC more often than not. This is a matter of honor (and perhaps paranoia) among Amateur Radio operators.

Secondly, in the event of a national emergency, the fed will order a complete cessation of all private radio communications and require the FCC to enforce such radio silence. (This was the case during WW2.) Amateurs will monitor their bands to maintain such a ban.

All members of a group should be assigned a "tactical call-sign" by mutual agreement among local groups. Names, nick-names, and CB "handles" must never be used, since these quickly give away the identity of the operator to a monitor.

[A good format for tactical calls is a 3-character group, like the Navy uses. Usually one digit and two letters make a good format.]

ANTENNAS:

Keep them simple. Mobile and portable antennas will need to be short, compromise design monopoles (whips) or wire dipoles (strung up on fishing line between trees, etc.). A good antenna tuner (antenna matching unit) will be needed if multiple frequencies are to be used with a single antenna. Short, mobile antennas (e.g. "loaded" whip designs) are usually very narrow-band structures, providing a good "match" (without a tuner) on a range of only 10 or so kilohertz on the low end of the HF band.

TRANSCEIVERS:

Most modern HF sets sold today cover the 3 to 30 MHz band (some Amateur Radio sets tune from 1.8 to 29.97 MHz, and some military man-pack sets tune 2.0 to beyond 30 MHz). The receivers are usually continuous tuning, but the transmitters may be band-limited. ICOM and Yaesu are good choices for Amateur sets. SGC makes commercial /para-military HF sets and sells to Amateurs and others.

The set should have a DC battery pack, or operate from nominal 12 V DC sources (mobile). A set with an AC-only supply is not much use except in a motor home that has AC power.

A built-in ATU (antenna tuning unit or matching unit) is desirable unless you intend to operate only on a very narrow frequency range.

Some older man-pack radios may be available that tune 2.0 to 15 MHz. These will work fine, since each group will have dedicated CB radio sets for that band (upper end of the HF band). With the solar activity now making the ionosphere unstable, the upper end of the HF band will not be as useful as it was some years ago.

COMMON TERMS:

AM - Amplitude Modulation / modulated.

AME - AM Equivalent - SSB signal with carrier not suppressed, to allow reception via ordinary AM receivers.

DX - Distance - abbreviation, in common usage, long distance.

FSK - Frequency-Shift Keying / keyed.

HF - High-Frequency (3 to 30 MHz band by definition; 2 to 30 MHz, Military usage)

Hz - Hertz. Unit of frequency, cycles per second.

kHz - KiloHertz. 1000 Hz or 0.001 MHz.

LSB - Lower Side-Band.

MHz - MegaHertz. 1,000,000 Hz or 1000 kHz.

Net - Network.

OTH - Over the Horizon (beyond line-of-sight distances).

PEP - Peak Envelope Power. The peak RF power of an AM signal.

PWR - Power - abbreviation.

RTTY - Radio Teletype or radio teleprinter.

SSB - Single Side-Band - AM mode transmitting only one side-band, usually with suppressed carrier.

SW - Short Wave. Old name for the HF band.

USB - Upper Side-Band.

W - Watt. Unit of power.

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