"Simplex Operations, Procedures and Equipment"

Based on a 1998 article by

C. Edward Harris, KE4SKY, AEC Fairfax ARES

INTRODUCTION by David Fordham, KD9LA

Licensed radio amateurs and their communications equipment can be indispensible in times of public emergency ... only if they are trained and prepared to serve as efficient communicators.  Untrained and unprepared operators simply get in the way and hinder recovery efforts.  Simply being active in the hobby is not enough to prepare us and our equipment for the rigors of service under dire and disaster conditions encountered in real emergencies. 

The information below is based on an article written by C. Edward Harris, KE4SKY.  It gives guidance and suggestions to the new technicians and extra class licensees alike.   All hams should read, study, and take to heart the information below.


If amateurs take repeater systems for granted and depend on them, then we are less able to respond during an emergency. If one or more repeaters go off the air from icing, wind damage, power failure or other incident, the remaining ones become overloaded. It is difficult to coordinate regional activities if everyone tries to use the same few repeaters!

Realistic disaster training anticipates that some or all of the local repeaters may be unavailable. In the aftermath of a severe storm, repeaters may be on battery power, which must be conserved, so we can't expect repeaters to always be there to compensate for our weak individual stations.

Local and regional ARES response plans must designate when and where simplex is appropriate.  The plans must include provision for managing communications if one or more repeaters go down.  And hams must be proficient in communicating without the benefit of repeaters.

If a public service event covers a radius of only a few miles, try using simplex instead of tying up a machine. Use repeaters for talk-in and to reach areas with poor simplex coverage, but don't encourage their use for your primary working frequency.  Practice keeping repeaters clear for priority traffic.

Operators need to know their assigned simplex frequencies to use for local nets, coordinated with surrounding jurisdictions, which follow approved band plans and channelization!


New ham classes should stress operating skills, procedures and "good amateur practice" beyond the minimum needed to just "pass the test." Public service events and nets should be more than simply periodic on-air meetings.  They should be training ground to help new hams gain knowledge, experience and confidence needed to become responsible, skilled, effective communicators.

Nets and exercises should stress when simplex is appropriate and demonstrate how and when to change from repeater to simplex operation. Instruct operators to listen to a repeater's input frequency. If both stations have good copy, then change to simplex instead and free the machine, if there is no need for others to monitor your traffic.

New operators need to be taught the importance of using plain language, correct "pro words" and ITU phonetics on phone and how to program a new frequency, offset and CTCSS tone not already in memory. Other training topics on our net include safety, preparation and use of equipment, directed net procedures, NTS message handling and relays to operate effectively in a simplex environment.

Stations should use weekly nets as a reliability check of their emergency equipment, instead of using commercial power. On simplex it is very important to leave pauses between transmissions and to open the squelch to hear weak or distant stations, instead of keeping it tight to reduce noise.  Such "repeater habits" may require retraining.


Hand-held transceivers are not adequate as primary rigs for emergency communications! Having "only an HT" limits users to nearby repeaters or simplex within a few miles. If an HT signal is so weak that it cannot be copied, it takes double the air time and battery consumption from others to provide relays, repeats or fills to get that traffic through. New adult operators should buy 50w mobiles as first rigs, because they cost little more than an HT, but have far superior simplex performance. HT's are sensible for commuters using public transportation and younger family members who don't drive, or as a spare.

If a repeater goes off the air, operators need adequate power to continue on simplex, including listening for and relaying weak stations. Offer new operators guidance on how much power is appropriate on simplex compared to working repeaters. Always stress the minimum power needed for reliable communication, but also remember that with simplex, the emphasis should be on RELIABLE!

Operators need adequate ERP to get their traffic through the first time, but should not waste limited battery capacity by inefficient use of excessive power, which causes interference to distant stations they cannot hear and violates standards of good amateur operating practice!

Transportable VHF operators for county-wide nets need at least 25 watts PEP and a 3db gain antenna elevated 15 feet or more above ground elevation. Directional antennas on portable masts are needed for "getting in" from outlying areas. Hand held users need adequate battery power to maintain 5w PEP into a higher gain directional antenna, such as a 3 or 4-element yagi, or to augment their HT with a 25-30w amplifier and elevated omni-directional antenna, such as a J-pole. Fixed stations need equivalent ERP and battery or other auxiliary power for 24 hours.

If a repeater is "down," nets should meet on the repeater's output frequency simplex. Pauses of 2-3 seconds between transmissions exemplify good amateur practice and are essential on simplex to enable stations with priority traffic, needing fills or relays to break in as needed.

Don't depend on having a regular Net Control!  Every ARES operator should know how to call up and run a net, because in an emergency your regular net control may be busy elsewhere!  Everyone is an alternate net control. Just jump in there and do it! It's great training.

Most ARES / RACES nets follow a similar format which resembles NTS procedure. NCS comes up on the working frequency and asks if it is in use. If the frequency is clear, call the net, briefly state its purpose, that it is directed and promptly get down to business.

Ask if there is any emergency or priority traffic, then pause. If there is any, deal with it immediately!  Next call for liaisons from other nets or organizations, or stations with traffic. Ask if there are any relays and direct stations copying a weak signal to do so.

Emergency nets don't take check ins to build a roster, but to match needs with assets.  NCS asks who has traffic or information and relays the information or instructions, determines which stations can handle it, deals with it as it comes and moves on. If the net is not busy, traffic may be passed on the net right there. If traffic is heavy, NCS will direct the inbound and receiving stations off frequency to pass their traffic while the net proceeds and instruct them to check back in when finished. Moving an entire net in unison to an alternate repeater or simplex should be done only as a last resort, because some stations may get lost in the shuffle.


ARES organizations must be prepared to operate in high RF environments in close proximity to transmitters from other services. We encourage transceivers capable of both CTCSS encode and decode to help reduce interference, but when the squelch is open you may still need help. We have found notch filters perferable to helical cavity bandpass filters for IMD supression, because they are useable with dual-band rigs, are less expensive and appear to be more effective than a bandpass cavity when a strong near-field source desenses the transceiver.

For instance, Fairfax ARES has a Diamond X-50 dual-band antenna on Fair Oaks Hospital, at 477 ft. AMSL, within 20 ft. of a paging transmitter in a rooftop environment with multiple commercial and public safety users. Side-by-tests over a month proved the Par Electronics VHFDN152 notch filter significantly more effective than a DCI-146-4H helical cavity bandpass. Without the filter, a Kenwood dual-band transceiver was so heavily desensed that the 147.300 Bluemont and 146.955 Rockville repeaters, normally received +40 db over S9 varied from S3 to barely readable.

The VHFDN152 filter eliminated almost all paging noise whereas the DCI "can" did not. While up 40 db of desense was still apparent when the pager was active, reliable repeater contacts were possible throughout the DC Metro area into West Virginia up to 80 miles away. Simplex 2 meter contacts were adequate to reach hospitals in neighboring counties 15 miles away, simply not possible with the DCI bandpass cavity in that particular environment. Low-loss UHF pass-through permitted contacts on 445.925 between the hospitals within Fairfax County.

All-mode rigs which don't receive outside the 2-meter band are less susceptible to intermod than mobiles having wide out-of-band receive and pull out weak FM signals below the noise discerned by typical mobiles. Weak signal rigs are real plus for your primary NCS.

Dual-band rigs highly desirable, because UHF is more effective than VHF in built-up urban areas. We use cross-band repeat to conduct nets from deep within shelters or hospitals and may use parked mobiles as portable cross-band repeaters to reach into low lying areas with poor simplex coverage.

The 220 MHz band is quiet, less affected by intermod than 2 meters, gets out of buildings well and has good simplex propogation. If enough of your operators have 220 gear, it provides another asset for voice or packet or as a command talk-around for issues you don't want on your operations net.


The importance of increased antenna height cannot be stressed highly enough (pun intended!) A 4-element yagi up 15 ft. with 25w from an HT+brick amp out performs 100 watts into a typical mobile whip mounted down on the car trunk lid. If you don't use a portable mast, at least drive to a high spot away from power lines to operate! If you don't have a surplus MS-44 mast kit, use a plastic bucket filled with concrete to hold a support pipe and 3 to 4 five foot sections of TV mast or a telescoping painter's pole!

Using a portable mast mounted base antenna or yagi enables you to use less power to save your batteries. We encourage our operators to develop what they call "tactical mobile" capability (minimum 25 watts, 3 db gain, 15 ft. mast, 24 hours battery power) so that we can go anywhere to call a net and cover an area without worrying about access to fixed facilities on short notice.

Some of our operators use a radial adapter which enables a mobile antenna to be attached with hose clamps and elevated on a portable mast. The rest use a small dual-band base antenna of at least 3db. Cushcraft's AR-270 dual-bander is only 3.75 feet high, 5/8 wave on 2m and collinear on 440. It fits into a car trunk when assembled, its performance and VSWR are also acceptable on 220 and it's great for portable use or attic installation where there are restrictions on outside antennas.

While many mobile VHF operators use 5/8 wave 2-meter whips (which also work as a 1/4 wave on 6 meters) some mobile simplex operators prefer higher gain collinear mobile antennas such as the Diamond SG7900 or Hustler CG144. For bicycle or motorcycle mobiles, fiberglass van or camper shells, good choices are dual-banders which are half-wave on VHF (Diamond SG7200 or Comet CX-224) or mono-band half-waves which provide unity gain without the need for a ground plane.

For fringe area operation, 3 or 4 element yagis such as Cushcraft's A148-3S or 124WB are compact, have good gain and a wide useable pattern. They can be used effectively in a fixed position without frequent re-aiming required of a long-boom, contest Yagi. Color-code the elements. use wing nuts to ease field reassembly without tools and store in a capped PVC pipe in the trunk.


It is basic to emergency operation that stations have battery or other auxiliary power sufficient to operate for at least 24 hours. One amp-hour per PEP watt of battery capacity should always be available. Powering a mobile rig from the car battery works well for a few hours, but during an emergency gasoline is scarce and it is wasteful to run the engine for 10 minutes out of every hour to keep the battery charged.

The best technical solution is to equip a vehicle with dual batteries and isolation circuitry from a boating or RV supplier to separate the "starting" battery from the "comm" battery, then to add a solar panel and charge controller to keep both batteries charged when the vehicle is idle.

A lowest-cost option is to carry a boxed deep cycle battery and fully-automatic, low amperage charger such as the Schumacher Electric Mod. SE-1-12S (available at Wal-Mart, $25).

You should also pack some basic tools, AC extension cord, DC power cords for your mobile rig or HT brick amp with your "Go Kit," packet gear, portable mast, antenna and 50 ft. of extra coax.

A common mistake among inexperienced operators is failure to plan enough batteries to last all day! "Barefoot" HT operators need at least a pair of 12-volt, 2ah gel cell batteries, or an extra NiCd pack, AA battery case and two sets of spares.

For portable operations requiring movement in support of SAR or wildfire suppression, a BCI Group U1 33ah gel cell or AGM battery weighs 25 pounds, fits in a GI .50 cal. ammunition can, and is adequate to run an HT brick amp all day.

A pair of Group U1 battteries powers a portable repeater or packet station for 48 hours if you limit PEP to 25w. For continuous operation alternate batteries, charging in 8 hr rotations.

If there isn't a means to recharge the batteries, the net control station needs a Group 27, 95 ah battery to run around the clock. AGM batteries are used in military vehicles and by the US Coast Guard for severe service. A Group 27 Concorde Life-Line series (65 lbs., $179) with aircraft-type cell construction is UPS shippable from West Marine, (1-800-BOATING) and fully adequate to power your HF-SSB or 150w VHF amp all day.

Despite their wide use by amateurs, gel cells are NOT "the answer" for emergency service. They are not deep cycle and depth of discharge greater than 25% significantly reduces their life. They cannot be used below -20oC, in engine compartments of vehicles or in uses subjecting them to temperatures above 50 degs. C. Gel cells larger than 5 amp/hours can be left on a fully- automatic, low amperage charger without harm, but should not be allowed to charge above 14V or float endlessly without an automatic shut-off.

The usual failure mode of dry NiCds used in hand held transceivers is not "memory" effect, but either deep discharge causing cell reversal or diminished capacity caused by excessive charge current or prolonged slow over charging. The general rule for charging dry NiCds is to increase the rated voltage by 15% to overcome internal resistance and charge at a current equal to 10% of the battery capacity, times ten hours.


We do not recommend for ARES the use of mag mounts constructed using RG-58 coax having a solid center conductor. This cable is suitable only for permanent vehicle installations where it will not be subjected to repeated flexing. We recommend that factory installed crimp-type UHF connectors on mag mounts be cut off, replaced with solder type and the cable reinforced behind the reducer with heat shrink or tape. Frequent flexing eventually causes failure of the shield at the connector, always at the worst possible time.

The best simplex performance always results from the most efficient antenna, at the greatest height above ground elevation and shortest run of low loss feed line, providing the highest ERP for the least battery consumption.

A unity gain, quarter wave mag mount thrown on top of the nearest metal object may work fine for local repeaters, but on simplex will be lacking, unless you have height and a "straight shot."

We recommend use RG8-X for HF runs less than 100 ft., jumpers and VHF less than 50 feet. Use RG-213 below 100Mhz for runs up to 200 ft. and 9913F above 100 MHZ. for runs over 50 feet and for all above uses 200 MHZ.


Before we can be of service to our communities, we must follow the primary rule, a rule so important that the Boy Scouts have made it their motto:   "BE PREPARED"!  When the time for action arrives, the time for preparation is over.  Often, this moment comes unexpectedly.  So please, do your part.  You never know when your assistance might make the difference between inconvenience and complete disaster.


This page is maintained as part of the
Massanutten Amateur Radio Association's
Web Page series.

David R. Fordham, KD9LA

This page last updated:  12/21/13