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Thursday, October 22, 2020

A Look At Modulation



A Back to Basics Column from November 2018

From the Canadian Basic Amateur Radio Question Bank

Back To Basics is a regular column in the SARC Communicator Newsletter, available at:  The Communicator Digital Edition: Amateur Radio Newsletter (ve7sar.blogspot.com)

It is a subject that is important because of the interference overmodulation can cause...

This month we’ll look at percentage of modulation and overmodulation. In all the exams I have administered, this topic is always covered. It’s important because it has the ability to cause significant issues on the air. The impact of this is highlighted by the fact that it is repeated a half-dozen times in the Canadian Basic Question Bank with slightly different wording, for example:.

B-001-019-004

The maximum percentage of modulation permitted in the use of radiotelephony by an amateur station is:

A. 100 percent

B. 50 percent

C. 75 percent

D. 90 percent

When you transmit a signal, you do so over what’s called a carrier frequency. This is a relatively constant oscillation, usually in the radio frequency band, that gets modulated (altered) by the signal. In terms of radio use, the modulation is generally (but not always) a waveform produced by the human voice, music or other audible means.

For example, either the amplitude or the frequency of the carrier gets modified (or “modulated”) by the signal, hence “AM” – (Amplitude Modulation) and “FM” – (Frequency Modulation).

When this modulation is so large that the carrier signal clips (distorts, in the case of AM) or the frequency changes to such a degree that it goes beyond the range that the receiver can pick it up or overlaps other carrier frequencies (in the case of FM), the signal is said to be overmodulated.

Likewise, if the signal is of such small amplitude or frequency variation that it cannot be picked up or adequately amplified by the receiver (because of background noise and/or the strength of the carrier frequency), it is said to be undermodulated.

Overmodulation is the condition that prevails in telecommunication when the instantaneous level of the modulating signal exceeds the value necessary to produce 100% modulation of the carrier. In the sense of this definition, it is almost always considered a fault condition. In layman's terms, the signal is going "off the scale". Overmodulation results in spurious emissions by the modulated carrier, and distortion of the recovered modulating signal. This means that the envelope of the output waveform is distorted.

In the image, an amplitude modulated sine wave:



  • At 0% unmodulated [top left], the sine envelope is not visible at all;
  • Less than 100% modulation [top right] depth is normal AM use;
  • At 100% modulation depth [bottom left], the sine envelope touch at y=0. Maximum modulation that can be retrieved with an envelope detector without distortion;
  • At greater than 100% modulation depth [bottom right], "overmodulation" occurs and  the original sine wave can no longer be detected with an envelope detector.

Therefore, the answer to our sample question at the top of this article is A. 100 percent.


~ John VE7TI

18/11



Sunday, October 18, 2020

Tech Topics: Filters, Diplexer and Triplexer Fundamentals


A Popular Communicator Article from 2018 

Several stimulating discussions around the Saturday morning club breakfast table have taken place recently in connection with our use of bandpass filters, diplexers and triplexers.  This article is designed to remove some of the mystery surrounding these devices, which we use both at the OTC and at Field Day.  Although the discussion relates to HF devices, the same general principles apply to VHF and UHF.

Introduction

As propagation conditions change throughout the day, week and year-to-year, HF stations need to have the flexibility to change to those bands which are open. Typically 20 m is open during the daytime hours with 160, 80 and 40 m opening up in the evening and nighttime hours.  In years when sunspot activity is greater, 15 and 10 m also open up during the day.  Currently we are near the sunspot low with the result that DX contacts are a challenge at any time of the day with only the low bands consistently productive for DX.

 

Ideally, a transceiver will utilize an independent antenna for each band on which it operates.  However this is not always possible, where space does not permit or when several transmitters are operating simultaneously (at Field Day, for example).  So we may deploy a multi-band antenna in conjunction with electronic devices that will allow more than one transmitter to use this single antenna, so long as each transmitter is operating on a different band.

SARC’s first exposure to these electronic devices was ca 2015 when we acquired a set of bandpass filters and triplexer for use with our 10-15-20 m TH7 beam antenna.  This was successful and allowed us to have the one antenna on a high tower serve multiple transmitters without significant mutual interference.   


Then a couple of years ago at Field Day, we began using an off-centre fed long wire for 40 and 80 m.  During the late evening hours these two bands were the only game in town, so the antenna was in demand by two stations simultaneously.  Again, a triplexer and bandpass filters allowed this to happen.  Alas, one of the devices failed at the critical time. 

In 2017, we acquired an identical set of the devices described above for use at the OTC, where we have a tri-band beam for 10-15-20 m plus an OCF dipole for 40 and 80 m.  Once again, the 160-80-40 triplexer failed during use.  

This could not continue as failures in these devices place expensive radios in danger of serious front-end damage (i.e. smoke) due to strong other-band signals not being adequately blocked.  It was time for serious reflection about our physical setup.  

A Review of Some Basics 

Inductors tend to pass lower frequencies and capacitors high frequencies.  In other words inductors have a low impedance to low frequencies and capacitors the reverse, the resultant reactance or impedance depending on the value of the inductance, capacitance and frequency.  

An inductor connected to a capacitor will have a unique frequency at which the pair resonates, called the resonant frequency.   At exact resonance, the inductive reactance equals the capacitive reactance expressed as XL = XC and the impedance will either be very low or very high depending on their parallel or series configuration.  The effect of resistance in any practical circuit does not change the resonant frequency but it does affect the sharpness (or Q) of the tuning.

In other words, an inductor in series with a capacitance has a low impedance at its resonant frequency, but the same pair connected in parallel exhibits a high impedance to the flow of current.  These properties are the basis of many types of radio circuits, used most notably for tuning purposes.  They can also be deployed in various combinations as RF filters and in power supply filters to change pulsating DC to “pure” DC.

A low pass filter will pass low frequencies and block high frequencies.  A high pass filter does the opposite.  Bandpass and bandstop filters allow a band of frequencies to pass or be blocked, respectively. The figures above show the generalized frequency response of the 4 basic filter types. 

Below are some simple examples of L-C circuits used in practice for the various kinds of filter devices.  The presence of R in the circuits represents loads but otherwise does not affect the general type of filter and can be ignored for the sake of this discussion.



Intuitively, it is not difficult to determine which type of filter it is by examination of the circuit, if you think of the way L and C respond to low and high frequencies, whether in isolation, in series or in parallel when presented with a range of different frequencies.  

More complicated circuits have been devised that improve the performance of these basic circuits and make them more useful.  A study of such devices will bring forth variations named for the engineers who studied their properties, such as Butterworth, Chebyshev, Cauer and Bessel.  More complicated circuits are not within the scope of this introductory article, but a comprehensive discussion can be found in any ARRL Handbook.

The complexity of a filter circuit is described in terms of its “order”, a measure of the number of L and C elements.  Here, for example, is a 4th order high pass filter:


Practical Devices

A diplexer allows two transmitters to feed one antenna or, conversely, two antennas to serve one transmitter (don’t confuse a diplexer with a duplexer, which is a different animal).  A diplexer simply consists of a low pass filter and a high pass filter operating in parallel, with the cutoff of each somewhere between the two operating frequencies.  With an HF unit used to separate 40 m (~7.0-7.3 MHz) from 80 m (~3.5-4.0 MHz), the cutoff frequency typically would be 5 MHz.   

A diplexer may be able to discriminate 80m from 40m signals by 20-40 dB.  While 20 dB represents a power suppression of the unwanted signal by a factor of 102  it is insufficient to protect the radio.  

That is why an HF diplexer is seldom used by itself.  A bandpass filter in series with the diplexer might suppress the unwanted frequency an additional 40-60 dB depending on its design.   So the diplexer and bandpass filter, operating together, would typically suppress the adjacent band signal by a total of 60-100 dB or a factor of 106-1010.  

If a triplexer rather than a diplexer, is desired to facilitate a third band, the problem becomes more complex.  The “middle” frequency would necessarily have to be a bandpass filter.

One problem is that the size of components for diplexers and triplexers for 160, 80 and 40m bands will be large.  This size factor and associated high cost generally make high power diplexers, triplexers and bandpass filters quite costly.  

Our Devices

Our Dunestar triplexers appear to be rather simple filter circuitry.  Why do these units fail repeatedly, even with the radios operating at 100 watts?  It can only be inadequate current or voltage ratings on the components or excessive SWR, or both.  This would suggest that the antennas connected to the triplexer should be close to resonant at the desired frequencies.  Operating at extreme ends of the band, especially under Field Day conditions when time does not always permit “tweaking” of their length, height or configuration may produce unacceptably high SWR.  

Here is the lesson we have learned: carefully research the characteristics of the diplexer or triplexer you are considering for purchase.  Not only are the band isolation and insertion loss important, but the need to have conservative voltage and current ratings on components is critical.  Then do not deploy these devices on antennas where a near resonant condition cannot be achieved.  



Conclusion

We will probably replace both our Dunestar 160-80-40 triplexers with more robust devices to ensure another failure does not happen.  Units available from VE6AM (www.va6am.com) and DX Engineering (dxengineering.com) and 4O3A (www.4o3a.com/products/high-power-filters/combiner/) are under consideration to meet this need. [In the end we went with VE6AM's product, which has given excellent service]

More good reading can also be found at: 

https://static.dxengineering.com/global/images/technicalarticles/lbs-pb-tp500_sn.pdf.

~ John VA7XB

18/09



Thursday, October 15, 2020

Back to Basics: Transformers

The Communicator Revisited - October 2018

From the Canadian Basic Question Bank

Back To Basics is a regular column in The Communicator Newsletter. Past issues are available at The Communicator Digital Edition: Amateur Radio Newsletter (ve7sar.blogspot.com)

B-005-11-1 If no load is attached to the secondary winding of a transformer, what is current in the primary winding called?

A.    Magnetizing current

B.    Direct current

C.    Excitation current

D.    Stabilizing current

A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. A varying current in one coil of the transformer produces a varying magnetic field, which in turn induces a varying electromotive force (emf) or "voltage" in a second coil. Power can be transferred between the two coils, without a metallic connection between the two circuits. Faraday's law of induction discovered in 1831 described this effect (See story Page 4). Transformers are used to increase or decrease the alternating voltages (AC) in electric power applications.


An ideal transformer is theoretical… lossless and perfectly coupled. There exists no lossless transformer though. Transformer energy losses are dominated by winding and core losses.  Magnetic permeability of the core results in the most loss, often felt as heat.

One of the main reasons that we use alternating AC voltages and currents in our homes and workplace’s is that AC supplies can be easily generated at a convenient voltage, transformed (hence the name transformer) into much higher voltages and then distributed around the country using a national grid of pylons and cables over very long distances.

A varying current in the transformer's primary winding creates a varying magnetic flux in the transformer core and a varying magnetic field impinging on the secondary winding. This varying magnetic field at the secondary winding induces a varying EMF or voltage in the secondary winding due to electromagnetic induction. The primary and secondary windings are wrapped around a core of high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With an AC voltage source connected to the primary winding and load connected to the secondary winding, the transformer currents flow in the direction indicated in the diagram below.


According to Faraday's law, since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of windings. This is determined by the equation:


The ratio of the transformers primary and secondary windings with respect to each other produces either a step-up voltage transformer or a step-down voltage transformer with the ratio between the number of primary turns to the number of secondary turns being called the “turns ratio” or “transformer ratio”. The transformer winding voltage ratio is thus shown to be directly proportional to the winding turns.

When connected to a source of AC power, current flows through the primary winding of a power transformer even when no loads are connected to the secondary winding. The primary winding remains an inductor and lets some AC current through despite its reactance. This minimal current is called "Magnetizing Current" Also known as the “Exciting Current”. This current establishes the magnetic field in the core and furnishes energy for the no-load power losses in the core. 


Therefore, the answer to our question is: 

A. Magnetizing Current.


~ 73, John VE7TI



Sunday, October 11, 2020

Google Home and Alexa In The Shack


An Assistant That Works for Free

Since 2017 I’ve become enamored with  personal assistants. No, not the kind that you have to pay regularly… the kind that connect to your home wifi system and make life easier.

There are three primary systems, depending on your operating system. Google Home and Amazon Alexa are probably the more common, while Mac users may prefer the currently less capable Siri, available on HomePod.

Google Home speakers, or the app enable users to play audio and speak voice commands to interact with services through Google's intelligent personal assistant called Google Assistant. A large number of services, both in-house and third-party, are integrated, allowing users to listen to music, control playback of videos or photos, or receive news updates entirely by voice. Google Home devices have integrated support for home automation, letting users control smart home appliances, plugs and lights with their voice. Multiple Google Home devices can be placed in different rooms in a home for synchronized playback of music. The device is able to distinguish between up to six people by voice. Google skills include hands-free phone calling in the United States and Canada; proactive updates ahead of scheduled events; visual responses on mobile devices or Chromecast-enabled televisions; Bluetooth audio streaming; and the ability to add reminders and calendar appointments. The wake-word is “Hey Google” or “OK Google”.

Amazon Alexa  is a virtual assistant developed by Amazon, first used in the Amazon Echo and the Amazon Echo Dot smart speakers. It is capable of voice interaction, music playback, making to-do lists, setting alarms, streaming podcasts, playing audiobooks, and providing weather, traffic, sports, and other real-time information, such as news. Alexa can also control several smart devices using itself as a home automation system. Users are able to extend the Alexa capabilities by installing "skills" (additional functionality developed by third-party vendors, in other settings more commonly called apps such as weather programs and audio features).

Most devices with Alexa allow users to activate the device using a wake-word (such as “Alexa”); other devices (such as the Amazon mobile app on iOS or Android) require the user to push a button to activate Alexa's listening mode.  It’s a burgeoning market, Amazon has more than 5,000 employees working on Alexa and related products. 

Microsoft and Amazon have a joint project to integrate Alexa into the Windows 10 operating system alongside Windows own personal assistant Cortana.

How does this relate to actual usefulness? In 2017, when these devices hit the market, I couldn’t decide which one to go with. Even now, Google and Alexa are in stiff competition to be the leader. Its like the old 8-track vs cassette or Beta vs VHS standards. Fortunately, many devices are both Google and Alexa compatible.

Aside from being able to turn on my smart TV by voice, listening to my music collection or a radio station on command throughout the house, and asking them for the weather report, the news or a joke, new skills for these devices arrive weekly, some more useful than others. Using a combination of Google Home and Alexa devices has given me a good insight into the capabilities (and weaknesses) of each. At this point, Google still seems to be the more useful of the two where my interests are concerned. A few examples. You can also get either a Google or Alexa device with a built-in screen.

I have installed a half dozen ’smart’ (meaning wi-fi enabled) lightbulbs and outlets. I have recycled all of my old mechanical timers. Often the power would go out and all of my timers required resetting. Now they pick-up where they left off and each goes on and off as required and on command through Google Home or Alexa—even from my smart phone or tablet when I am not at home. For an example, see https://youtu.be/Wq-dC61EH7Q.

There are now dozens of add-on 'skills' that you can instruct your assistant to provide you on demand. See Amazon.ca : amateur radio and Alexa Can Be Your Ham Shack Assistant! • AmateurRadio.com for examples. So now I can ask about band conditions, a space weather report or listen to a Ham podcast on demand.

One enterprising Ham, William VE4VR connected Google Assistant/Alexa up to his amateur radio (simplex or repeaters). His prototype is based on using a fresh IRLP hardware setup with a simplex VHF radio attached. He chose this as the starting point because he had a Linux machine with the radio and audio interface working. Once that was set up, he created a Google Assistant IFTTT (IF This, Then That) routine and integrated it with the IRLP platform. VERY cool!

When a radio user presses A[ssistant] or 0[perator] it calls the Assistant and then listens for voice commands. Google responds for custom questions/responses. Wake words might come later but need to be careful with sharing audio hardware. See the project video at https://youtu.be/jE_Ohi2nqIY.

In my eagerness to further explore, I found the low-cost Sonoff smart device. It is Google and Alexa compatible and it is an experimenter’s dream. I set up my garden sprinkler system with a 115VAC valve so that it will turn on at my voice command or though the software programmed timer. I already use it to turn on my workshop dust extractor… oh so many projects, so little time!

But back to Ham Radio… I wanted a low cost versatile way to turn station power on and off Using a Sonoff switch (I bought 6, making them about C$10 each). Now I walk into my shack and say: “OK Google (or Alexa), turn on my station” and everything lights up. The same happens in reverse when I power down. Sonoff also has low cost temperature sensors, water sensors and motion detectors, all of which work with the smart home controls.

~ John VE7TI

18/09



Sunday, October 4, 2020

New Fox Hunt (ARDF) Receivers Available Now

 

They work GREAT!

Second generation 80m ARDF foxhunt receivers designed by Les Tocko VA7OM and produced by Dave Miller VE7HR are now available.

The RX80M is ready to use, with no assembly required – comes complete with:

  • 9v battery
  • antenna
  • earbuds
  • internal 100 dB attenuator
  • tuning 3.51 MHz to 3.60 MHz 

Cost C$125.00 plus shipping by Canada Post/USPS or UPS Parcel.   

No volume or club discounts are available since the project is operated on a cost recovery basis by volunteers.  

To order, send email to JohnVA7XB@gmail.com and include:

  • Your name and callsign (optional)
  • Complete mailing address
  • Number of units required

Upon receipt of your order, further instructions regarding payment will be provided.

An instructional video describing how to use the RX80M is available at www.RX80M.com

Also… TX80M transmitters suitable for use with the RX80M will be available soon.

What is a foxhunt?  

Also called “radio direction finding”, It is a radio sport, a friendly competition to locate hidden transmitters using a handheld receiver which can determine direction of the transmitted signal.  It’s fun and it’s easy to learn the technique and you do not need an Amateur Radio license. 

There is an earlier post describing fox hunting at: 
The Communicator Digital Edition: Fox Hunting (ve7sar.blogspot.com)

 Check out the videos at: 

https://youtu.be/YK3gETNc2jU and https://youtu.be/DMEKWOyaAnc  


~ John VA7XB




Tuesday, September 29, 2020

A Windows 10 Tip For Hams

Keep those specific drivers from updating

Does this sound familiar? You install a new piece of hardware and finally get it working. Then Windows updates and it no longer works! Likely what has happened is that the device driver also updated and is no longer compatible. The solution for older Prolific PL-2303 HXA/X  clone chips used in serial to USB converters is to use a driver release older than vn3.4 Each time you turn your computer off, the latest driver is reloaded due to windows auto-update (or if you unplug and re-plug the device into a USB port). Note that this generally does not affect genuine Prolific devices.

To avoid that, a recent work-around exists and has been published by Microsoft. It's a tool named ‘wushowhide.diagcab’ (Show and Hide Update). It allow you to inhibit auto-update for a particular program or driver (Prolific in this case).

For more information and where to download this tool, take a look at this article: KB3073930 How to temporarily prevent a driver update from reinstalling in Windows 10.

I have tested it and it works fine. The only problem
with it is that it reloads the latest driver when you plug the device into a never before used USB port. So, if you change the place of connection, you should manually set the driver to vn3.3, but you have to do that only the first time you use this port. Next time, the driver remains at vn3.3 and never upgrades to vn3.6. 

More information: https://support.microsoft.com/en-ca/help/3073930/how-to-temporarily-prevent-a-driver-update-from-reinstalling-in-window

Download: http://download.microsoft.com/download/F/2/2/F22D5FDB-59CD-4275-8C95-1BE17BF70B21/wushowhide.diagcab 

18/09


Monday, August 31, 2020

The Communicator Magazine September-October 2020


Over 100 Pages Of Projects, News, Views and Reviews... 

Amateur Radio News from the South West corner of Canada and elsewhere. You will find Amateur Radio related articles, profiles, news, tips and how-to's. You can view or download it as a .PDF file from:  


http://bit.ly/SARC20SepOct




As always, thank you to our contributors, and your feedback is always welcome.
The deadline for the next edition is October 21st.


If you have news or events from your BC club or photos, stories, projects or other items of interest from elsewhere, please email them to communicator@ve7sar.net

Keep visiting our site for regular updates and news: https://ve7sar.blogspot.ca    

73,

John VE7TI
'The Communicator' Editor







CQ CQ CQ

A Look At Modulation

A Back to Basics Column from November 2018 From the Canadian Basic Amateur Radio Question Bank Back To Basics is a regular column in the SAR...

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