Squelch

Squelch is a funny word that is familiar to many of us without understanding what it really means.  Hard to improve on the definition beyond that in the Technician license exam question:

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Most useful when using voice modes (phone), squelch makes radio operation more bearable by turning off the audio when there is no valid signal.  Without squelch our radios would be cranking out a lot of unwanted background noise.

The reality of both AM and FM radio (which we covered recently) is that there is electrical noise in the bands from many sources, natural and man-made.  This noise is often randomized so that it appears as hiss or fuzz (white noise) from radio receivers.  A squelch circuit mutes receiver audio to block the noise when there is no real signal.  Squelch acts as a noise gate which closes for random noise and opens when a real signal (such as modulated voice) appears on frequency.  How the squelch circuit determines what is a valid signal and what is noise varies; there are a few common techniques (refer to algorithm link in references below).

Squelch is built into more expensive broadcast receivers.  It may also be found on AM transceivers (particularly CB radios) and is a feature of nearly every FM amateur rig.

While less prone to electrical noise, FM technology is susceptible to a lack of true signal.  Traditional FM receivers use an LC tuning circuit that generates ‘hiss’ with no signal present.  You may have noticed this while tuning between stations  on your broadcast FM radio.  Since hams commonly use VHF/UHF FM transceivers for local chat and EmComm work, the squelch feature of our rigs is of particular interest.

Squelch setting is important because if you make it too tight you may not hear a weak signal; too loose and you get constant noise.  General good practice (at least a starting point) is to turn down the squelch until you hear background noise (hiss), then increase the threshold until the noise goes away, then just a little more.

Squelch threshold is always settable on your FM transceiver.  There may be a knob to turn as in the example below, or it may be through keypad menu.

Squelch Adj FT7900

Squelch tail is a common term that is related to all this.  The tail is the brief “pfffft” sound heard when another station stops transmitting.  Audio example on YouTube here.  It is the natural presence of noise during the delay between the time a signal drops and the squelch kicks in.  On a repeater it will often followed by an audible beep or similar courtesy tone.

So far we have discussed the basic squelch feature of common ham radio transceivers. There are other squelch techniques in common use with repeaters such as CTCSS, DCS, and PL.  These fall into a separate category called Tone Squelch, mainly because they have a different purpose and functionality.  We may discuss this in a future post.


Some Useful Links

Squelch setting – W3ATB blog

Squelch algorithms – PA3FWM site

Squelch Tail – DAP-COM reference

 

Generator Use & Safety

Spring is [hopefully] coming soon with expected turbulent weather.  A new hurricane season is also upon us.  Both are liable to cause disruptions to utility electrical power.  Annual ARRL Field Day is also approaching.  Time to think about auxiliary power generators.

Small gasoline-powered generators are relatively common and widely available for emergency or portable electrical power.  It’s a good idea for the prepared homeowner to have one, mainly to keep the fridge/freezer cold during times of sustained power outage.  The savvy radio amateur also recognizes the importance of communications capability in a blackout scenario as well.  Power is needed to make our radios work beyond what limited battery capacity we have, particularly in emergency situations.  Most EmComm groups include generators in their plan and have them on hand.  Not every ham does.

Honda Generator

Consider having a small generator for essential power when the lights are out for hours.  Having a generator is good; knowing how to use it safely is the focus of this topic.  We will look at four related safety considerations:

  1. Carbon Monoxide hazards— CO
  2. Fuel handling and storage (fire)
  3. Generator grounding
  4. Shock hazard

Carbon Monoxide (CO) is the primary hazard with generators, since  CO is produced in the exhaust of all gasoline and natural gas combustion engines. 

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NEVER, ever run a generator inside a dwelling or garage where exhaust can seep into the occupied space.  CO is a colorless and odorless gas which can kill or injure humans and animals.   It can be detected only with chemical or electronic CO detectors; it’s wise to have detectors in every home.

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Always operate a power generator outdoors in a well-ventilated area. Continue reading

Family Comms Plan

One of the more useful applications of ham radio (beyond the obvious enjoyment of the hobby) is for emergency communications (EmComm).  In times of man-made or natural disaster, mobile phones and internet may be inoperative or unreliable.  In such times ham radio may be the only way to communicate.

WhenAllElseFails

Extend this idea to your loved ones with a family communications plan.  This would involve you, a spouse and/or children. For it to be practical all would need to be hams with at least a Technician class license.

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A family communications plan would be established and written down for all family members to have near their radios.  This would include primary, secondary, and tertiary repeaters in your area.  Also include a simplex frequency and the national call (simplex) frequency in case the repeaters aren’t working or are tied up.

Make sure to test all frequencies between expected locations (home, work, school) with a dry run to discover any interference or lack of coverage.

To help visualize how this might work, let’s say there is a major tornado outbreak that wipes out a large chunk of a mid-sized city one weekday afternoon.  Dad is at work, Mom is at home, and daughter is at school.  Cell phones (voice & text) and internet are not working so none of these people can let each other know where and how they are.  All three members know that the situation is bad so all get on their radios.  Primary and secondary repeaters are busy with dozens of other local hams reporting in damage and trying to reach their families.  Tertiary repeater is open so all three move there.  From his mobile rig Dad reports that he is fine and will make his way home ASAP.  With the base radio Mom reports minor damage with a fence section down.  With her HT Daughter reports that the college is unaffected but has to wait for clearance to leave campus.  All can share updates as needed, and may have to wait their turn on the repeater.

Great idea, but you may have objections.  Let’s address a couple of these:

  1. Getting everybody licensed.  The necessary Tech license is actually pretty easy to obtain.  Five year olds can do it with a little study and coaching.  Not a good excuse.
  2. Cost.  License exam fee is $15 or less.  Many hams already have at least one VHF/UHF FM radio.  Cheap HTs (minimal requirement) can be had for less than $50 each.  Money should not be an excuse.

The licensed family member can train/coach the others to get a license and work on getting more radios.  It may be that they already have multiple radios (base at home, mobile in car, one or two HTs) so all that is needed is establishing the plan and testing it.

Local comms using VHF/UHF is most important in disaster situations but you could extend this beyond line of sight to more regional or national distances using HF equipment.  It gets more complex in this case and practically speaking a General class license would be needed.  Here also non-voice messaging using WinLink may be useful.

An interesting article on a surge in US licensees for EmComm purposes including family members is found here.

Repeater Reverse

If you aren’t familiar with VHF/UHF repeater operation, now is a good time to review it here.  Repeaters are frequently used for chatting with local hams, regular nets, and EmComm use.

An occasional problem with repeater operation is when a weak transmitter doesn’t have enough power to keep the repeater’s squelch open.  That is, you can tell someone is there but hear little or no signal.  Could be that the transmitter is in a sheltered location, doesn’t have a good antenna, or using too little power.

For whatever reason, they can’t break through with a strong enough signal to be heard.  If you suspect this is happening, you can try listening to them directly instead of through the repeater.  It’s possible that you are closer to the weak transmitter than the repeater is.

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Many hand-held radios (HTs) and mobile VHF/UHF transceivers support this with a repeater reverse function, typically by pushing a button on the radio.

Kenwood Reverse

Recall that a repeater re-transmits what it hears on a different frequency.  The difference in transmit and receive frequencies is called repeater offset and this minimal difference is needed to allow for sharp filtering between them so that the strong transmit signal doesn’t damage sensitive receiver circuitry.

By selecting reverse on a transceiver you then listen to the repeater input frequency instead of its output.  In this manner you can get the weak transmitter’s true signal strength and quality, not what the repeater re-transmits.  This assumes that you are receiving better than the repeater, which is a possibility but not a certainty.

Useful when you want to see if a weak signal Continue reading

Distress Call

It’s unlikely that you will hear a radio distress call but hams should know how to respond to one.  Hopefully you will never need to send a distress call yourself but it’s best to know how to call for help in an emergency.

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While some situations may be questionable, if life/health/property are genuinely threatened, it merits a distress call.  Basically, if you would want police, fire, or ambulance response, it’s a distress scenario.

Obviously if one is in town with a telephone nearby, the proper response is to call local emergency services (in USA, dial 911).  But if the phones are down or someone is very remote, radio may be the only way to communicate.

Distress calls are formally done by voice mode using the term Mayday-Mayday!  SOS is the CW mode or Morse visual equivalent of Mayday; you are even less likely to encounter it.

If you hear a distress call:

First of all, stop whatever you are doing (QSO, or whatever) and cease all transmissions to avoid interfering with the distress call or a response.

Second (very important!), write down everything you hear related to the distress call.  Under duress, people tend to forget things and stress will be high at both ends of the radio.  Details about the incident are crucial for sending help.  Include the date, time, frequency and mode.

Third, see if anybody else responds. Perhaps there is another station in a better position to react (location, facilities, etc.)  If nobody else does, briefly ID and ask what is the nature of the incident.  The distress station may not have a call sign or know proper radio procedure; be prepared to work with a non-ham at the other end.  If time permits, confirm the details you wrote down with the distress caller.

Fourth, determine how to help the distress station.  You need to get them help, but that depends on the location and nature of the trouble.  If unclear or uncertain, contact local emergency services and let them help you sort it out, even if the distress is far away.  In any case you must relay important detail such as the type of emergency, how many people are involved, and the distressed party’s location.  The Mayday caller may also provide specific guidance if they are trained and knowledgeable.

Lastly, maintain contact with the distress station and emergency responders until help has arrived and the danger is passed.

Know also that in a genuine emergency/distress situation, you can violate normal protocol and rules to assist another station, at least in the USA (probably most other countries as well).  If it requires using a mode, frequency, or power level for which you are not authorized, do it!

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To send a distress call should you ever need to:

If the phones are down, use your VHF/UHF radio on a local repeater or national simplex frequency where other hams are likely  to copy you (choose the most active local repeater).

If you are very remote and there is no chance any line-of-sight radios can pick you up, Continue reading

Traffic

New hams listening in on a local net are likely to hear the net control station begin the session by asking for stations with traffic.  Seems like there never is traffic, so what’s that all about?

Traffic is ham-speak for passing messages, usually via regular radio nets.

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Messages are almost always formal, written on a form with bureaucratic detail.

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Even friendly, casual messages (“happy birthday, Aunt Edna”) are typically passed this way.

ARRL Radiogram

Such messages (traffic) resemble the old telegram format.  They go back to the very early days of amateur radio when passing messages was a primary function.  In fact, this is from where the US Amateur Radio Relay League (ARRL) derives its name.

Nowadays traffic is mainly an emergency communications (EmComm) function, although the occasional casual message is passed on.  Purpose-specific traffic nets meet regularly to pass messages to stay in practice for when they are really needed, like when there is a local or regional communication outage.  Likewise, local nets support traffic to maintain readiness.

The general traffic flow is from an originating station to a local net where the message is Continue reading

Clutter

New hams, don’t hesitate to make that first radio contact.

Experienced hams, don’t hesitate to try a new band or operating mode.

Technician and General Class hams, don’t hesitate to upgrade your license class.

All hams, don’t hesitate… on the air.  With your mic keyed to transmit, don’t fill up time and space with “um…”, “well…”, “er…”, “aah…” and other such sounds of hesitation.

It’s not only annoying to hear but hesitation really clutters up the airwaves.  In certain cases it impedes more important communication.  For example, during a special event operation or true emergency communication (Emcomm) situation or drill, the Net Control Station (NCS) is constantly talking to various stations.  If you’re using up valuable time on the air, other stations cannot be relaying their info.

A good rule of thumb or general practice is to know exactly what you will say before you key the mic.  Think first, then talk.

If Net Control asks you a question that you cannot immediately answer, don’t take 20 seconds to stall or explain away your delay, just reply that you will get back to them.  This frees up the net for others and lets the NCS know to expect a reply shortly.

The opposite of hesitation in radio work is brevity .  Keep your transmissions short, few, and far between in a special event or Emcomm scenario.

Don’t call in periodically just to let the net know you’re still there.  Net Control and the rest of the net assume you are there unless you have to drop off for a valid reason but you must inform them in such case.

Don’t use 50 words where ten would do. Unfortunately, some hams are long-winded on a special event net.  It takes forethought and practice to keep a report short and simple.   Use the minimum number of words to communicate effectively.

Don’t talk to sound important or just to hear your own voice.  This is heard occasionally on a special event net; others can usually tell when this happens and it’s aggravating.

Study up on Emcomm radio practices, guidelines, procedures and etiquette and then practice these.  Drills and special events are perfect exercise.  Refer to our “EmComm Toolbox” topic for such info.

Another form of clutter to avoid during a special event or Emcomm operation is speculation.  Rumor, guessing, second-hand info, and supposition often lead to confusion and unnecessary concern.  Just the facts, ma’am.  Seriously, only give solid facts.