SWR

AF5NP Analyzer, Antenna, Impedance, Standing Waves, SWR (Standing Wave Ratio)

The standing wave ratio (SWR) is an important topic to hams regardless if they are working HF, VHF, UHF or any other frequency range allocated to radio amateurs.  Unfortunately it is technically involved and somewhat complex so is not intuitive or easy for non-technical folks to understand.  We’ll give a simplified explanation of SWR here and give you a basic idea of its significance and how hams relate to it.

The simplest way to think of SWR is as a measure of impedance matching.  Most commonly it is looking at the impedance differences between transceiver, transmission line (more often coaxial cable), and antenna.

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Assuming that all modern radios and cable have 50Ω impedance, the real SWR of interest boils down to the match between the transmission line and antenna.

As we mentioned in a previous post, when impedance of a source equals load impedance the best possible signal coupling occurs. Conversely, when impedances are not the same, signals couple poorly.  This is true of all electronics circuitry involving AC waveforms.

In amateur radio SWR focus is on transceiver to antenna coupling where we want to maximize RF power transfer in both transmit and receive modes.  When impedances do not match, received signals will be weak or non-existent; when transmitting, power will not radiate well from the antenna.  The ideal or “perfect” SWR for best possible transmit/receive coupling is 1:1, meaning a 50Ω radio/transmission line to a 50Ω antenna.

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SWR is simply the ratio of two impedances being measured.  It is commonly expressed in the X:X format and the larger value is always given first, regardless of which side is higher.

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With a 50Ω radio and 50Ω coax cable, a 4:1 SWR could indicate either a 12.5Ω or a 200Ω load (antenna).  Similar examples for 50Ω cable are contained in the General class exam pool:

G9A09-2015G9A10-2015A ham’s main concern with high SWR is significant power reflected back from the load, which stresses the transmitter power amplifier.  While a 1:1 SWR is ideal, practically speaking, 1.5:1 or less is good.  Many modern transceivers automatically reduce transmit power with a SWR greater than 2:1.

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SWR can be measured Continue reading →

Call Sign Order (Calling Protocol)

AF5NP Identify/Identification, Protocol

Ground Control to Major Tom
Ground Control to Major Tom
Take your protein pills
And put your helmet on

With all due respect to David Bowie and his classic song Space Oddity (which most of us probably know well), the lyrics are arranged for rhyming, not for good radio practice.

“This is AF5NP calling K5ZFA”.  If you heard this on a repeater, would it be OK?  The answer is that it is legal but the call sign order is backwards and contrary to protocol.

You may hear a new ham (or a very distracted old timer) on the air identifying first, followed by their target station.  That’s not right.

Well-established radio procedure is calling or identifying in a To-From sequence (call sign order).  Whether answering a CQ, calling a station on a repeater, or simply identifying the two parties in a contact, the other station call sign is given first, followed by your own.

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Using our example above, the proper protocol would be, “Calling K5ZFA, this is AF5NP”, or in its most minimal form, “K5ZFA, AF5NP”.

Note that the basic To-From protocol using just the two call signs satisfies requirements and is well understood on the air.  K5ZFA would hear AF5NP calling and may return the call in the same manner (“AF5NP, K5ZFA”).

This to-from sequence is so ingrained that when the order is reversed other stations are likely to get confused; there is a risk of mistaking one station for the other.

Another reason for using this sequence is that it is normal and natural for a ham to alert on their own call sign.  When it is given in the to-from way, they will tend to pay attention to what comes next, which should be the calling station’s call sign.  Reversing this order means the called station is likely to miss the calling station’s ID because it was given first and they weren’t paying attention until they heard their own ID.

New hams should make this their practice and before long it will become second nature.

So don’t model your call sign order after Space Oddity, no matter how cool the song.  It should have been, “Major Tom from ground control” but that would have changed the flow of things.

Why Hams Care About Solar Activity

AF5NP DX, HF (High Frequency), Ionosphere, Propagation, Solar, Sun

As we learned in an earlier post on the ionosphere, the real magic in ham radio is skywave propagation where HF  band (and sometimes VHF) signals can travel well beyond line of sight (over the horizon), even to the other side of the planet if conditions are right and radio waves may bend back to earth in the ionosphere.

The sun is largely responsible for energizing the ionosphere and affecting its quality (height, density, thickness, disturbance).  Unfortunately for hams, solar activity is highly variable, not constant.  There are periods of excellent skywave propagation when the sun is busy and then times of poor propagation when the sun is quiet.

Solar_Cycle_Montage
Montage of Sun’s activity over 10 years (solar cycle 23)

This topic is very complex and not completely understood.  Study is ongoing and radio amateurs have contributed greatly to the science; much has been learned in the last 100 years or so since radio became a real thing.   Great detail is found below in some excellent web links.  A brief summary of how solar activity influences the ionosphere is presented here:

  • Our sun tends to be active in 11 year cycles, on average
  • Sunspot counts are a general indicator of solar activity
  • Propagation on higher frequencies is more influenced by solar activity than the lower frequency bands.
  • Ionospheric condition is influenced by the Earth’s magnetic flux lines.
  • Earth’s magnetic field is strongly influenced by solar wind (largely a day/night phenomenon but solar wind can spike with disturbances).
  • Solar flares, coronal mass ejections (CME), and coronal holes cause geomagnetic storms which affect or disrupt radio communication and create noise.

Solar/Space weather is a study of how solar events affect the earth’s magnetosphere.  A/K (long/short-term) indexes measure the stability of Earth’s magnetic field.

Hams worldwide who are active on HF and VHF bands pay a lot of attention to solar activity because of how it affects propagation and noise levels.  QRZ features N0NBH’s graphic summary of important solar and geomagnetic conditions on their main page as shown below.  Some hams and ham websites include this data on their own pages as well, so you may see this sort of info a lot.

S-T Data QRZ

Presently (2018-2019) we have days on end with no sunspot numbers, resulting in awful HF propagation (note sunspot number SN=0 above).

Solar Activity Level

Despite these poor conditions that limit decent phone (voice) and even CW (Morse) QSOs, hams can still make contact with domestic and international stations using some of the newer digital modes which can decode extremely weak (inaudible) signals.

We are hopefully approaching the end of the current solar minimum with dreams of increasing solar activity in the coming several years.

Solar activity is so important to hams that there are 16 related questions in the General class license exam question pool (only two with the limited privilege Tech pool).  Some Continue reading →

Other Resources for New Hams

AF5NP Amateur Radio, ARRL, New Ham, Podcast, Website

Here at NewHams.info we don’t pretend to be the ultimate authority or only game in town.  While we may have a lock on this website domain name, there are other truly useful and interesting sources with good information for new or prospective ham radio operators and we want to share some of these with you here.

The ARRL produces an audio podcast entitled So Now What?  It is a “bi-weekly podcast geared to those who are just getting started on their Amateur Radio adventure. Whether you’re new to the hobby or looking to get back on the air after an absence, we know that you’ve got lots of questions.”

You can access and/or subscribe on Apple and Android to listen in with mobile phones or you can link to a web stream via Blubrry here.

A page on N0JI’s website is entitled, For New Hams.  It has quite a bit of detail; topics include:

  • First steps
  • Equipment
  • Making contact
  • Service and groups
  • Preparedness
  • Activities
  • Just curious
  • Above and beyond
  • Assistance

eHam.net has an informational page:  Guide to Amateur Radio for New Hams.

St Louis radio club web page:  New Ham Radio User Portal.

Great website with tons of educational material, Ham Radio School: Basics

HRS also has a topic, I Got My License, Now What?

As other related new ham resources come to our attention we will update this post to add links.

Transmit Power

AF5NP Amplifier, Linear, Power, QRO, QRP, RF, Transmitter

Q. How much RF power can a ham legally transmit with?

A. It varies with frequency/band, license class and licensing authority.  Maximum transmitter power levels are regulated by country; we will discuss the rules in the USA here.  It is one of the important regulatory subjects covered by the question pool for amateur radio license exams.

The average VHF/UHF handheld transceiver (HT) puts out 5 to 10W maximum.  A typical VHF mobile rig is capable of 50 to 75W.  Most modern HF transceivers peak at 100W.

Before we get to maximum levels, in the USA the general guidance is to use the least amount of power needed.

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Of course, that’s easier said than done so many hams just go with the radio’s max power setting unless they know that a lower power setting works well or are operating a weak-signal mode.

In general, US hams are limited to 1500W (1.5kW) peak envelope power (PEP).  That doesn’t mean you should, just that you legally can.  This applies to General and Extra Class licensees for most bands and Technicians at VHF and higher.

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There are specific power limitations on 2200m, 630m, 60m, and 30m bands:

band_chart_image_for_arrl_web

As you can see from the band plan (based on FCC regulations), Technician class licensees have 200W power limits on the HF bands, with HF privileges rather limited already.

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So why a would a ham want to use more power than their stock radios can transmit, and how would they increase their default power level?

To answer the why question, it is simply that more transmit power gives more signal energy at the receiving end.  Increased wattage improves the chance of making contacts under poor conditions by overpowering signal attenuation and background noise.

To answer the how question, hams use RF amplifiers (linear power amps) to increase the power of their basic transmitter.

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This RF power amplifier must operate linearly so that it does not distort the waveform.

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RF amps can be for single or multiple bands.  More commonly you will find multi-band HF (or HF+6m) amplifiers which tend to be large boxes:

HF Amp

You will also find broadband or single-band VHF and/or UHF amplifiers:

Mirage 2m Amp

Besides all these commercially available amplifiers some hams build their own.  This is partly a nod to tradition—hams being DIY types—and partly because commercial amps may not be readily available for very low or high frequencies.

Ham-speak note:  When a ham says that s/he is running barefoot it means raw transmitter output power, unamplified beyond the stock radio capabilities.  Typically 100W or less.

Power amps are not just for handheld VHF/UHF FM transceivers; they can amplify most any amateur radio RF signal.  They are mainly useful for voice (AM, SSB, FM) and video Continue reading →

Why Hams Care About the Ionosphere

AF5NP Distance, DX, HF (High Frequency), Ionosphere, LUF, MUF, NVIS, Propagation, Skip, Solar, Sun, VHF/UHF

There are many questions concerning the ionosphere and its layers in US license exams.

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Experienced hams talk about the ionosphere a lot these days and we see plenty written on the topic in amateur radio websites and magazines.  So what’s the importance of the ionosphere?

The real magic in ham radio is skywave propagation where signals can travel well beyond line of sight, even to the other side of the planet if conditions are right.  We can have two-way radio communication between Iceland and Australia and places in between because voice, video and data signals may be bent back to earth by the ionosphere.

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The ionosphere is shell of electrons and electrically charged atoms and molecules (ions) that surrounds the Earth, stretching from a height of about 50 km (31 mi) to more than 1,000 km (620 mi).  Because this band is electrically active the ionosphere is able to reflect or refract electromagnetic radiation at certain frequencies, the HF bands in particular.  For most hams communicating beyond line of sight is a big deal and the ionosphere is what makes long distance (DX) contacts commonplace.

Ionosphere bending

There are two defined ionospheric layers at night and four in daytime, the difference being exposure to the sun which provides most of the energy to the ionosphere.

Ionosphere_Layers

In daylight the F layer separates into F1 and F2 regions.  Because F2 is farthest from the earth’s surface it can bend radio waves the greatest distance.

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Long-distance propagation changes with day/night cycles and seasonal variance away from the equator.  There are numerous anomalies and disturbances that can affect the ionosphere.  Between all these factors the ionosphere is not a uniform shell; it has varying height, thickness, and density.  This continually changing area makes HF propagation highly variable.

Also known as skip, ionospheric propagation of shortwave (HF) radio signals travel a specific radius or skip distance from the transmitting antenna.  This makes received signals particularly strong at the skip distance.

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In addition to single skip distance, the earth itself can reflect/refract signals from the ionosphere back up, resulting in a secondary skip or hop and perhaps Continue reading →

Ham Radio Bands

AF5NP Band(s), HF (High Frequency), RF, VHF/UHF, Wavelength

The term band is thrown around constantly in ham radio discussion and it is included in  many questions in US license exam pools.  So what exactly is a radio band?

Parts of the radio frequency spectrum allocated for a common purpose are called a band.  Besides amateur radio, the reader may be familiar with USA commercial broadcast ranges known as AM band and the FM band, or another personal communication chunk of frequencies called the citizens band (CB).

With amateur radio, bands are generally associated with a number (2m or 40m, for example).  This number is approximately equal to the wavelength of that span of frequencies

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We say approximately because a specific wavelength is only valid at one exact frequency and that may be outside the actual range of the band.

Shown below is a chart of the current US amateur bands (dated 2017):

band_chart_image_for_arrl_web

These 18 bands are are named by their approximate wavelength.  For those who care about such details, the named wavelength (λ) may not actually be inside the designated frequency range.  A table of these is given below:

band wavelengths

Some do, but why don’t all the meter bands line up with wavelengths inside the band?

Lots of discussion on this issue can be found on the internet and two particularly good links are given in the first two references below.  It’s a real combination of history, simplicity, misuse, and existing broadcast band names.

0.7m is the same as 700mm or 70cm; the 70cm name is more commonly used Continue reading →