Education

Here you will find information to supplement the on-air educational training that we have during our weekly net.  Please feel free to request topics (or volunteer to teach one!) during the net, by dropping Charles an email, or by abusing using the Round Table Topic suggestion form.


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Decibels / Station Upgrades

posted May 11, 2018, 11:23 AM by Charles Boling

Signals strength/loss is very often expressed in decibels.

Riiiight! What's a decibel?


Mathematically, a bel is just the common logarithm of a number, and a decibel is 1/10th of a bel, 2 bels = 20 decibels.  A decibel represents a ratio;  it always compares two things -- like if I exclaim "This radio has twice the power!" and you wonder "Twice the power of WHAT?"

A short table of commonly-used values:
3dB = 2x (roughly)
10dB = 10x
20dB = 100x
30dB = 1000x

Gains/losses add (or subtract) together w/ decibels; for example, if you cut your radio's output power in half, you lose 3dB.  If you run it through a long coax cable that also loses half your power, you lose another 3dB; thus your total loss is 6dB (i.e. 4x weaker) -- your signal is 75% weaker (or 25% of its original power) at the receiving end. Incidentally, 6dB is the standard amount for one "S-unit" on a radio's received signal strength meter, or "S-meter".  So, if you manage to increase your power output by, say, 16x -- 16 is 4 x 4, or 3dB + 3dB -- you'll be 1 s-unit stronger at the other end (assuming that the receiving radio had a properly calibrated S-meter. Often they're very sloppy).

So how much stronger is an S-9 signal than an S-0 signal? If each of those 9 S-units represents 6dB or 4x increase, then the total gain is 6 x 9 = 54dB, or 4^9 = 262,144x.

Sometimes you'll see power expressed in terms of dBmW (decibels compared to 1 milliWatt; 1 Watt=30dBmW) or dBmV (power of received signal compared to one that produces 1 millivolt in a 50-ohm circuit; 1W = 77dBmV), but that's all I'm going to say about that, since I'm not addressing electrical engineers.

Practical examples

Everyone wants to get more effective power out of their radio so that they can talk further, but what can we do that's cost-effective?  Keep in mind that it doesn't help to yell louder if you can't hear the reply! You can shout across a large field using a megaphone, but if you want an answer back, then either the other person has to use a megaphone too, or you need a listening device (ear horn, anyone?) to hear them.  How many decibels do we get from some common things?

 FROM
 TO/after/with dB
 Low Power (0.5W) High Power (5W) HT
 +10
 5W HT
 50W Mobile
 +10
 50W mobile rig 200W VHF Amp
 +6
 100W HF rig
 1500W legal limit
 +12
 70cm rig
 100ft LMR-400 coax
 -3
 70cm rig
 100ft RG-58/U coax
 -11
 "Isotropic Radiator"
 1/2-wave Dipole antenna
 +2
 1/2-wave dipole   
 1/4-wave ground plane
 0
 1/2-wave dipole     Nice omni base antenna
 +6
 1/2-wave dipole
 14-element Yagi
 +13
 1/2-wave dipole
 Typical Rubber duckie
 -6
 Rubber duckie
 worn on belt at waist
or inside vehicle
 -15
 Good weather, best conditions
 Angry propagation gods, trees/antennas moving, etc.
 -30

Not listed in the above table is cost. a 150-300W VHF amp might run you $500 for a one-way 6dB; $150 invested in a better antenna/mount might get you the same 6dB gain both directions. Considering cheap coax? Consider again if you're working VHF/UHF -- losses are a lot worse than at HF, so extra money spent may be well worth it.  This is especially true when you consider that the higher the frequency and the higher the power you're at, the more expensive an amplifier is needed for any particular gain.  Legal-limit VHF amps are out of sight (in more ways than one). Even a 1kW amp can set you back $4k for "only" a 13dB gain for your 50W radio -- the same gain you could get by spending, say, $500 on a 14-element beam and a rotator.  (You may also be more able to make your own antenna than you are your own amplifier.)  Oh, with that amplifier, you might want a good low-noise receive pre-amp, and maybe a switching system to protect it from that 1000 Watts -- better figure another $1k just to be sure.

That's not to say amplifiers don't have their place. I live in an RF-quiet rural area, and talk to many people that are in cities with noise levels easily 6 s-units (36dB) above mine. They can't hear anything!   A linear amplifier that I can switch into the circuit when I want is an easy way for me to send them more power (while the amp adds noise and reduces my own receive sensitivity by at least 6 dB) and evens things out just enough to hold a conversation when conditions otherwise didn't quite permit it.  Many other times, it doesn't do me a lick of good.

Something else to point out is that conditions are extremely variable. Signals to my base station often fluctuate 30dB (5 s-units) and more, as trees our blowing near my antenna, the tower that a repeater's on is moving slightly, causing alternating constructive/destructive multi-path interference, rain is absorbing signals, etc.  So depending on where you're starting from, even an expensive equipment upgrade to the very best you can get, probably isn't going to change a signal from "can't hear them a bit!" to "consistent armchair copy" -- at best, it'll make them usable, and it'll take those marginal signals and make them great.

Let's try a couple of example station upgrades:

5W HT w/ rubber duck (near body) in house
+10dB upgrade to 50W mobile rig
+15dB mag-mount antenna on a cookie sheet/fridge
=25dB gain, or roughly 300x the effective output power. Wow!

50W 2m radio in house w/ mag-mount antenna on cookie sheet
+6dB Better antenna
+10dB Moved antenna outside and higher
-3dB 50ft RG-58 coax @ 148MHz
=13dB, or 20x gain. This is equivalent to a 1kW amplifier -- except that you've also improved your receive gain by at least 20x!

Note: In the typical house with lots of RFI-generating devices, moving your antenna up and outside can make a HUGE difference on receiving.

Monitoring Repeater Inputs

posted Jun 11, 2017, 7:16 PM by Charles Boling   [ updated Jun 11, 2017, 9:53 PM ]

It's sometimes very handy to be able to monitor the input frequency for a repeater.  (Less frequent, but also handy on occasion, is the ability to transmit on the repeater's output frequency.)  It's something that hams operating on VHF/UHF ought to be able to do -- particularly those who desire to be of service during an emergency when the need to communicate iis greater and the ability sometimes lesser.

Why would you want to listen to the input frequency:
  • If the person is relatively close to you, you may be able to hear them better than the repeater can.  If someone isn't hitting the repeater well enough to be understood, having an army of people listening for their simplex signal is invaluable.
  • Extreme example of the above: Repeater can't hear them at all because they're not transmitting the [correct] PL tone.
  • Their approximate location can be determined by how well various people can receive them
  • You can determine whether noise/distortion is being generated by their transmitter, or if it's being added by the trip through the repeater.
  • You can learn what simplex radio paths are/aren't effective -- planning for times when the repeater's not available.
  • If you're listening to a repeater and don't know what PL tone it requires, you can scan someone else's transmission to determine what PL they're using.  (Some radios have the ability to scan CTCSS tones).  Note that some repeaters are kind enough to repeat the PL tone (i.e. they output the same tone used to work them) so you don't have to listen to the input.

Why you'd want to talk on the repeater's output frequency:

  • If the repeater is down, most people will still be listening to its normal output frequency, wondering what's happening and when the repeater's going to be back up.  If you are able to reverse your Tx/Rx frequencies, you can talk to them (at least those who are in simplex range). Note that other people may live in areas with high RF noise and keep their squelch set high, so even if you can hear a weak signal clearly, they may not hear you.
  • If you can't hit the repeater but are near someone (and either they don't know you're there at all, or they're not smart enough to listen to the input freq) you can talk to them and they can relay for you to the repeater.   Note that talking on an active repeater's output frequency is not normally considered to be good practice, and it can be confusing for other repeater users, but if the situation calls for it, then you do what you need to do.  You may find it helpful to quickly inform you user that they're hearing you simplex -- not through the repeater (hopefully they get what you're saying) -- and warn them that most other people can't hear you, so they need to say what's going on and relay for you.

How do you listen to the input freqency?

There are several ways to do it. Many radios have a dedicated function to make it easier.  Let's discuss the ways:

  • VFO - This is the obvious way.  Switch from memory to VFO mode and tune to the input frequency.  Don't know it? You should! Example: W7DG Longview is 147.260 output, w/ + shift. Standard 2m offset is 600 kHz; therefore, the input frequency is 147.860 MHz. Some radios will display this frequency when you talk on the repeater channel.
  • Memory - This one takes preparation ahead of time.  I find it convenient to program a memory adjacent to the "normal" repeater channel w/ the Tx/Rx frequencies reversed. Then it's only one click of the knob or press of a button to switch back and forth between them.
  • REV button - Some radios (e.g. Yeasu) have a button that temporarily reverses the input/output, making it effortless.  Caveat: Often this will activate tone squelch (using the frequency of the tone you're sending to the repeater) so if someone is failing to transmit the PL tone, you won't hear them any more than the repeater does!
  • MONI button Other brands have a monitor button that temporarily opens the squelch, and, if in duplex (repeater) mode, switches to your transmit frequency to listen.  Unlike the REV button, this doesn't allow you to transmit, only listen.  On some radios (e.g. Icom) this button is a toggle; on others (e.g. Baofeng) it's a momentary -- only active as long as you keep the button down.



WWV

posted Feb 12, 2017, 7:14 PM by Charles Boling   [ updated Feb 12, 2017, 7:25 PM ]

Not part of the Amateur Radio service, but of interest to amateurs and other users of the HF bands, as well as people looking to find the correct time, WWV is one of the most well-known shortwave stations.  Not everyone is familiar with it, however, and I thought a brief overview of the WWV family of stations might be useful.


Current Stations

WWV

Location: Fort Collins, CO

Voice: Male (after HI)

Frequencies / Power (ERP) / Directionality:
 2.5 MHz
2.5 kW
 Omni
 5 MHz
10 kW
 Omni
10 MHz
 10 kW
 Omni
 15 MHz
 10 kW
 Omni
 20 MHz
 2.5 kW
 Omni
 25 MHz
 2.5 kW
 Omni
Services:
  • Audio reference tones: 600Hz (odd minutes), 500Hz (even minutes), 440 Hz (hourly)
  • Time: 1-second tick, 1-minute voice time announcement, continuous BCD date/time codes on 100Hz PWM tone
  • Reports: hourly reports on satellite health and propagation conditions, storm warnings

WWVH

Location: Kekaha, Kauai, HI

Voice: Female (before CO)

Frequencies / Power (ERP) / Directionality:

 2.5 MHz
5 kW
 Omni
 5 MHz
10 kW
 Westward
10 MHz
 10 kW
 Westward
 15 MHz
 10 kW
 Westward
Services: Same as WWV, except no 440 Hz tone

WWVB

Location: Fort Collins, CO

Frequency (kHz): 60

Power (kW):

Directionality: Omnidirectional

Services:
  • Time: continuous BCD date/time codes w/ DST/Leap indicators using PSK/ASK

Historical Timelines

WWV

  • 1919 - WWV call letters assigned to NBS (forerunner to NIST)
  • 1920 - Broadcast Friday night concerts on 500m/600kHz (50W AM) from Washington DC
  • 1921 - Agriculture market news broadcast on 750kHz (2kW spark gap)
  • 1923 - Broadcast Radio Frequency standards from 125kHz - 2MHz
  • 1933 - Moved to Beltsville, MD; Higher precision 5, 10MHz (30kW)
  • 1935 - Added 10,15MHz (20kW)
  • 1937 - Added 440Hz musical pitch, 1-second pulses, ionosphere bulletins
  • 1945 - USNO-synchronization; time announcements (Morse code)
  • 1946 - 30 & 35 MHz added (dropped in 1953)
  • 1950 - Voice time announcements every 5 minutes
  • 1960 - Digital time codes enabled self-setting clocks
  • 1966 - Moved to Fort Collins, CO
  • 1967 - GMT instead of local time
  • 1971 - Current BCD digital time code; voice announcements every minute
  • 1972 - First leap second broadcast
  • 1974 - UTC instead of UTC
  • 1991 - Solid state memory used instead of drums for voice recordings; DST notification improved and year added

WWVH

  • 1948 - Began on 5, 10, 15 MHz (1kW) from Kihei, Maui, HI
  • 1956 - 2kW, more accurate
  • 1964 - Voice announcements
  • 1965 - 2.5MHz (1kW) added
  • 1971 - Moved to Kekaha, Kauai, HI, current power levels, female voice, new digital time code  (telegraphic code turned off)
  • 1991 - Solid state memory

WWVB

  • 1956 - KK2XEI broadcast experimental carrier on 60 kHz @ 40W (then reduced to 1.4W) from Boulder, CO
  • 1957 - LF proved to provide more stable time reference than WWV/WWVH
  • 1960 - WWVL began operation in Sunset, CO on 20 kHz
  • 1963 - WWVB broadcast from Ft. Collins, CO on 60 kHz @ 5kW, enjoying better propagation due to good soil conductivity and not being right next to mountains
  • 1965 - BCD time code enabled self-setting clocks
  • 1972 - WWVL (now 2kW) went away
  • 1999 - Power increased to 50 kW ERP; consumer WWVB-synchronized clocks became commonplace

What good is WWV* to amateurs?

Time Reference

Yes, you can also get the time of day from the Internet using NTP, or over the telephone, rather than via RF.  Isn't choice great?

A precise short-term time reference can also be handy for calibrating computer clock for synchronized protocols like Slow-Scan TV

Frequency Reference

Want to check / adjust the accuracy of your VFO?  Zero-beat to WWV; it's accurate to a few parts in 10^13 (Yes, that's better than one part in a trillion -- that's a millionth of a Hz for the 10MHz signal).  That's far more stability than you'll ever need for your puny transmitter!

Want to check your sound card? The audio tones from WWV are still the gold standard in terms of frequency stability.

Propagation Indicator

This is the #1 use for HF operators, whether amateur, commercial, or government/military.  Quick, how many HF beacons operating in the amateur bands do you know the details (frequency, location)?  They're out there, but can you name some?  Thought so.  How about WWV? After reading the material above, do you remember any of the frequencies or the locations?  It's hard to beat the utter memorizing convenience of "Colorado Man, Hawaii Girl" exactly every 5 MHz (plus 1/2 the bottom one).  Add to that a nice AM voice format (you don't need to know Morse code, or remember specific call signs or time slots) that's receivable by about anyone on anything, and you've got something useful.  By checking the signal strength from Colorado & Hawaii on various frequencies, you can make predictions for amateur bands above/below them, to places closer/farther than the time stations.  No, it won't tell you if 10m is open to Finland, but it can tell you a lot.

In spite of the ease of remembering the WWV frequencies, if your HF rig is new enough to support memories, you might find it handy put program them; that way you can quickly switch between them for comparison with a single keypress, instead of having to type the frequency out every time.

Reliable signal source

It's always on, from a known location and power, and strong enough that you're all but guaranteed to pick it up on at least one frequency, and usually several (which you can usually guess roughly based on the time of day), making it a handy way to test/demonstrate a receiver system.  Calling CQ and not getting a response? The nice man in Colorado will always talk to you.

U.S. Call Sign History

posted Sep 11, 2016, 9:02 PM by Charles Boling   [ updated Sep 11, 2016, 9:48 PM ]

Ever wonder about "W" vs. "K" call signs in the Amateur service, or how someone got that particular "weird" callsign assigned to them?  Here's a good article from the 1994 QST magazine on the history of call signs (attached).

And a Wikipedia article on U.S. licensing:
https://en.wikipedia.org/wiki/Amateur_radio_licensing_in_the_United_States

Want to see what the current systematically-assigned calls are?  See the lower right corner of this page:
http://www.hamdata.com/fccinfo.html

Ham Radio for Home Schoolers 2016

posted Apr 22, 2016, 6:34 PM by Charles Boling

We just finished week 6 of our first series, with 20-25 active students.  I decided to post copies of the slides that I used during class, for convenient review by the students.  Anyone is welcome to look them over, though you may not get much out of them without the accompanying lectures!

They're available here in PDF format, through Google Drive.

I'll continue to add to the collection each week until the series is complete.


2014-2018 Technician Class Exam Question Pool

posted Mar 14, 2016, 11:46 AM by Charles Boling   [ updated Mar 14, 2016, 11:58 AM ]

This is the question pool for the Technician Class exam.

At the top is a hyperlinked table of contents showing the topics addressed by the various subelements.

The links don't work right on this page, but click here to open the original file, which will work correctly.




2m vs 70cm coverage

posted Feb 12, 2016, 10:43 AM by Charles Boling

Using a similar process as I did several years ago to generate some RF propagation plots such these, I compared coverage on both UHF and VHF from up on Rainier Hill.  I eliminated the geographical map background this time to make it easier to focus on the propagation rather than exact locations. Each pixel represents a 500m square, so the 600x600 plot covers a 150km radius, and you can pretty much figure out mountain placement, etc. from there.  The westward rays on the 2m plot are over the ocean.
440 MHz plot
146 MHz plot
146 + 440 MHz plot

Repeater Duplexers

posted Jan 18, 2016, 9:13 PM by Charles Boling

I was looking at some of those little mobile duplexers, and was amazed that they could do VHF, and get as close as 3.5 MHz for 70dB separation, while being so small.  I became curious as to how they were constructed -- and how tight the frequency adjustment was (i.e. could you use them for a range of frequencies without readjusting).  As it turns out: very tight -- they're 100% notch rejectors, not high/low filters or pass cavities, so both sides need to be pretty exact on the frequency of the other in order to attain a decent suppression of the unwanted signal.  I found a nice little easy-to-understand article on duplexers at EMR.  In fact, they have a collection of 8 articles on repeater filters and such; I'm looking forward to reading the rest of them.    And, of course, if you're looking for info to help you understand repeater construction better, there's always a wealth over at http://www.repeater-builder.com/.

VE Seminar Training Slides

posted Aug 16, 2015, 8:14 PM by Charles Boling

Yesterday was a training seminar for Volunteer Examiners.  The slides used in the presentation may be downloaded at
http://www.lakewashingtonhamclub.org/wp-content/uploads/2015/08/VE_Training_Seminar_Aug_15_2015_final.pdf

RDF Primer

posted Jun 25, 2015, 11:52 AM by Charles Boling

In conjunction w/ Field Day this weekend, I'm again hosting a bunny hunt (a/k/a fox hunt or T-hunt) at the CARS site in Colton.  I thought it was high time that I wrote down some of the information & tips that usually spew out of my mouth at the beginning of a hunt for newbies -- if for no other reason to keep my ramblings more organized.   Attached to this article is an outline containing some info on radio direction finding.

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