Events

SARC Events
Fall 2020
2019 FoxHunt
Video
2020 Courses
Next Basic Course
Field Day
Video

Friday, January 1, 2021

The January-February 2021 Communicator


110 Pages Of Projects, News, Views and Reviews... 

Happy New Year! The first issue of The Communicator magazine for 2021 is now available for viewing or download at bit.ly/SARC21JanFeb

Read in over 120 countries now, we bring you 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:  

bit.ly/SARC21JanFeb


As always, thank you to our contributors, and your feedback is always welcome. 

The deadline for the next edition is February 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


Sunday, December 27, 2020

My Return To Ham Radio

 One Ham's View...

Like many hams, I got licensed at a young age and was active through my later school and early adulthood years, but amateur radio then faded into the background as the responsibilities of life, family and career took precedence.  I was licensed as VE7CPT in 1977, at the age of 17, and over the next five to ten years “dove in”: I got my “Advanced” license, designed and built equipment, became a DXer and half-serious contester, explored packet and satellite communications, and even got onto 2m EME – still the “coolest” thing I have done in amateur radio! 

During this period of time, I also graduated university, got my first “real job”, got married, started an interesting career in the Vancouver Police Department, got divorced, eventually re-married, and began assuming significant supervisory and managerial responsibilities at work.  I also went to graduate school, completed three years of research and a thesis, and contributed to an advanced 56 Kbps wireless networking project.

I became VE7ZD in the late 1980s after meeting the ten-year advanced license requirement and spending three years on the “two letter suffix” waiting list.  Such were the regulations in those days!

Field Day… Kevin built a ‘lemon’ battery
and made some natural power contacts


For me, like many others, amateur radio operation had to “take a back seat” to the responsibilities of life, and twenty years flew by before I realized it.  During this period, while I maintained my station, towers, and qualifications, I operated rarely, maybe once a year.  Probably ten years went by without me making a contact on HF.

My interest in radio and communications technology, and my love of amateur radio never died, though, and I always knew that one day I would return to the fold and become active again. 

I finished my policing career in 2011, and after about seven years of being involved in other professional pursuits, I made the decision to return to the ham world earlier this year.

Kevin’s ‘other’ career… commercial airline pilot

This story is about my observations after returning to the hobby after a long absence. 

How has amateur radio changed?  In summary, the “ham radio” I see today is closely aligned with the hobby I left.  The people and enthusiasm are the same, and the debates are similar, but the context has changed significantly due to the immense impact that new technology, both analog and digital, has made upon radio and communication systems.

One difference I have observed is the wide variety of complex gear that is now available to the average ham at an affordable price.  Devices like handheld antenna analyzers can now be bought for a couple of hundred dollars.  The capabilities and performance of these devices far exceeds that of devices that were unheard of in the amateur community, and that cost in excess of $100,000. 

The development of new digital modes such as PSK31 in the 1990s, and most recently FT8 and its related weak-signal modes have greatly improved the effectiveness of ham communication.  While there are detractors, more communication ability is always better than less, and it is notable that FT8 has come along just at the right time: at the bottom of one of the worst solar cycles in recent memory.  Oh, for the summer of 1979 – global communication with 5 watts SSB on 10 metres, almost 24/7!

Incidentally, new modes in amateur radio are always accompanied by negativity from the established amateur community.  This will pass, as did negativity about SSB from the “AM” crowd in the 1950s.  In fact, this skepticism is one of the aspects of amateur radio which has not changed in my absence.

The advent of DSP and software-defined radios is also a major development over the past 20 years.  Like most other new technologies, initial skepticism gave way to utility, and the SDR has found its way into just about every ham shack.  The thought that you would be able to buy a receiver for under $10 that runs on 5 volts and covers 10 MHz through 2 or 3 GHz would have been laughable in the 1980s.

Innovation within amateur radio has persisted, and I see many projects that build on (especially) SDR and other new technologies to produce great new modes and communication capabilities. 

One thing I do note, however, is that the percentage of electronic experimenters within ham ranks seems to have dropped.  There are fewer amateurs building their own gear, and more “buyers” who simply acquire products and deploy them.  Innovators are fewer than they were before.

This may be understandable, as these new technologies are quite complex compared to the earlier amateur era, and more technical background is necessary for an individual to innovate, i.e. to invent new modes or techniques. 

I think that one reason for this is that amateur licensing standards have failed to keep pace with the development of new technologies.  This is the case in Canada, the US, and in other nations as well.  The licensing standards have taken modest strides towards inclusion of material covering DSP and SDR, for example, but not in enough depth to provide individual amateurs with enough technical background to invent or innovate, as they were able to in the past.

It is a difficult problem, and I am not advocating an increase in complexity or difficulty of amateur licensing!  Amateur radio plays many roles: emergency communications; public service; a reserve of technical talent; - finding the right balance is what is important. 

Hams are not, nor should they be expected to be, electrical engineers, but licensing standards should always reflect the technologies in use.  Compared to twenty years ago, I think that some aspects of the standards should be revised to better reflect use of current technologies within the hobby.


Kevin presents a SARC-SEPAR workshop on GnuRadio

I think that the average ham today is much more aware of the important role amateur radio can play in public service and

emergency response than was the case a couple of decades ago.  Public service and emergency communications has been part of amateur radio’s focus going back to the 1930s at least, but I have noted much more emphasis on this role since my return to the fold.  Public service and emergency communications plays a more prominent role in clubs, and even in popular magazines like QST.

Society’s dependence on telecommunications for day to day life is much greater than in previous decades, and hence the impact of a disaster, for example, could be much greater.  Amateur radio’s stronger focus on public service is good, because (as we all know), commercial infrastructure usually fails in a disaster despite the “best laid plans” of the major telecom providers.  Amateur radio will be able to help as it does not depend (as much) on this infrastructure.

Back to more specific observations.

Use of repeaters seems, for some reason, to have declined.  I hear a few VHF/UHF nets during the day and in the evening, but the idea of a repeater as a “watering hole” is no more.  One used to be able to find other hams 24/7 on local repeaters.  The repeaters still exist, but it just seems that hardly anyone is using them.  Perhaps the rise of smartphones, or the ban on use of handhelds while driving is responsible, but I think that the sense of “community” that was enabled through heavy usage of local repeaters has been eroded.

Fewer hams are active on HF, it seems, and those who are newly licensed are less inclined to want to upgrade themselves and their stations to utilize HF.  This is a shame, in my opinion, as the challenge and fun of HF communications, and in making contacts (and possibly friends) across the world is something that is personally satisfying. 

I understand the counter-argument – “what’s the point of putting together an expensive HF station for unreliable communications when I can just email or group chat internationally over the Internet at no cost?” – but this argument is weak in the context of amateur radio’s role in emergency communications and disaster response.  I think we need to emphasize amateur radio as “unmediated direct communication without reliance on commercial infrastructure”, and that this aspect might elicit more interest in HF amongst new (and younger) hams.

Younger hams: this is an important observation.  I believe that amateur radio has largely lost its innovative “spark” to the “maker movement”.  In the 21st century, young “makers” exploit technology to undertake all manner of interesting tinkering and research, and the movement has been the source of many technological innovations. 

When you read QST from the 1920s and 1930s, this innovative spirit was the purview of young hams.  Radio was fairly new and represented the bleeding edge of a lot of industry and government research.  Radios and antennas were (relatively) affordable to build and maintain.  Young people got involved and their tinkering led, in many cases, in the discovery and development of new technologies.

Computing hardware and software has become the area of current industrial innovation, and naturally many young people today have been drawn to this interesting field.  They are experimenting and creating, just as young hams in the 1930s did.  The proliferation of cheap computing devices such as the Arduino and the Raspberry Pi, global networking, and open source software support affordable experimentation, and one can see the appeal of “making” to young people.

What I find ironic is that many in the “maker” community are now interested in wireless devices and applications but have no experience with or understanding of radio science or technology.  There are almost endless discussions on “maker” forums and mailing lists about antennas, radio propagation, and the like, and most of the information being spread is totally incorrect. 

Makers are fumbling about and trying to re-invent the wheel in regard to wireless communications.  Most of these technical questions on “maker” groups were answered about a century ago by experimenters within the amateur radio community. 

I think that our amateur radio organizations, both in Canada and the US, missed (or are missing) a great opportunity to contribute to innovation and to technological literacy in general.  Our partnership (or even leadership) in the “maker” community would support amateur radio and help spread our skills to a younger generation.  In return, we would learn much ourselves.

Why the missed opportunity?  Every organization (and even radio clubs and individuals) tends psychologically, and unconsciously, towards a parochial position and can feel threatened, or at least uncomfortable, when others want to use “technology invented here”.  We have to maintain self-awareness and see the bigger picture.  “Makers” would make great amateur radio operators.

I’ll stop here for now, but summarize my observations by saying that I’m enthused to be back, the amateur community is alive and well, and the hobby still presents great opportunity for fun, learning and public service to all those who get involved.  In that sense, amateur radio is unchanged from twenty years ago.  See you at the club and on the air!

~ Kevin VE7ZD


 

Monday, December 14, 2020

HamShack Hotline

 

Yet another emergency communications option

Started in 1998, Hamshack Hotline (HH) is a FREE dedicated Voice over IP (VoIP) telecom service for the Ham Radio community. It is incorporated and not for profit.


You may ask: “Why do we need this?” In an emergency, it is proven time and again that any communications are an asset, and as Amateurs, that’s what we do best.

The next SARC Communicator will have a complete story on this service, and suggestions on how to get started. I did a presentation via Zoom about HH at our December meeting and since then 3 members have joined with more indicating an interest in joining.

It was pretty lonely on HH here in Surrey but the map is getting fuller...

HamShack Hotline as of 20-12-13 - https://www.google.com/maps/d/viewer?mid=1Awk65-qRwUWTGWaN3TjOO63GSoJJyu_3&usp=sharing 

I'm not feeling as lonely anymore.  Watch for story in next Communicator https://ve7sar.blogspot.ca

Watch this video for an overview: https://youtu.be/dMr9a_6CuNE

Lots of additional information on the HH FaceBook page as well: https://www.facebook.com/groups/hamshack

~ John VE7TI

Thursday, December 3, 2020

More On SDR Dongles

 

A Closer Look

We had an earlier article about SDR and SDR dongles. I recently played with a nano version. It is probably a knock-off of the NooElec.

I can tell you my findings:

  • It has to be connected on the USB computer port with an extender, otherwise the electric noise generated by the computer makes it unusable and completely deaf.

  • It has not much shielding it; acceptable if it is not case to case to the electric noise generator, but at several centimeters apart, it is fine. I tried to shield it in metal, and it did not make any difference, in various test situations. I suspect it is already shielded somehow inside, or partly shielded inside.

  • In the commercial FM band it is a cheap stereo and more important, an RDS receiver. It knows to display the name of the station, the songs that are played in that moment and whatever digital info the station sends in addition to the analog signal. The sensitivity in FM is way worse than 2 microvolts. Any dedicated commercial receiver amplifier, including my roommate’s Yamaha 2 micro V (and every single FM radio in the apartment we have, including clock radios, MP3 portables (the radio part) are more sensitive than the SDR dongle. Also, I am using a proper dipole antenna on the balcony, connected with coax cable to the SDR dongle, while all other 7 receivers have just a small piece of wire. I estimate somewhere at 30 – 50 microvolts sensitivity in the 88 – 108 MHz band.

  • The characteristics differ very much on the Rx bands and require adjustment from the RTL dongle settings. That means RF Gain; RTL AGC; Tuner AGC. It seems it does not like the 50 MHz band and the sensitivity is not great in this band. I confirmed the bad findings of everybody writing about this issue on the Internet.
  • In the 144 MHz band, with a good dipole, it receives everything the Kenwood 7950 and the Chinese walkie-talkie receives. It likes this band and it has good sensitivity. All repeaters from Victoria, Port Angeles, Nanaimo, Cowichan are 59.
  • It also likes the marine band, air traffic band and the weather band. They are all around 150 MHz and once the settings are done for one station, they can be kept in the weather, marine, 2 meter bands.
  • It is stable. I did not feel the need for a more stable oscillator. It did require adjustment in the software, -200 ppt for my dongle. This is considered a huge adjustment. I verified with encapsulated quartz oscillators (32 MHz, 125 MHz, 150 MHz, the 28.197 CW beacon), and indeed it needs that huge adjustment.

  • The CB band and the beacon on 28.197 MHz (VE7MTY, Pitt Meadows, continuous, CW) are in a band where the RTL dongle is not so sensitive. The beacon (nearby me) booms in my SONY ICF7600G portable radio, with its telescopic antenna. The SDR dongle with a CB whip on the balcony receives it almost OK, but only because I was hunting for the beacon and I knew where it is. The beacon’s signal barely produces a trace in the display spectrum, and I am nearby it (exactly 13.89 km away).

  • There are images everywhere. The FM band (88 – 108 MHz) can also be received on 30-50 MHz. The worse thing to do is to use an upconverter, as I saw so many on the Internet, with an NE612, and wide non-tuned input. I tried, and the images kill any useful signal. In the end I did 2 converters, in order to cover 3.5 MHz to 30 MHz, one for the lower part and one for the upper part. I used NE612, attacked by an amplifier with a BF998 in front. I have a tuning circuit just at the antenna, and 2.4 K resistor + coil in the output of the BF998 drain. The source terminal is connected directly at the ground and the BF998 is power supplied with 9 V (12 V is max in datasheet, and it does burn-up beyond 12 V). The oscillator is an encapsulated 3.3 V powered oscillator, in a socket, to easily changed. The best it worked for me is at 150 MHz, so stay away from FM commercial band and upconvert the shortwaves into a sensitive band that the SDR dongle likes. I can adjust the signal from the oscillator to the value from the NE612 datasheet, but actually it does not make any difference even if it is provided with 3 V (NE612 has a buffer in it before the mixer).

  • The only program that totally works in Windows is SDR Sharp. It has plugin to decode CTCSS tones and display their value. All other programs partly work (not all modulation types; there are workarounds for stereo; workarounds for drivers and so on). SDR Sharp simply works, all options, everything that the hardware is capable of.

  • The noise of the first element in the SDR dongle must be better than the BFR91A. I tried a wide range untuned amplifier with 1 BFR91A, and it did not bring in anything, just noise. The situation changed when I put a SAW 88 – 108 MHz (3 pin filter) in front of the BFR91A, and it helped.

  • It does not run hot. Whatever other users noticed with old SDR dongles is no longer an issue with my SDR small dongle.


[Right] This is my upconverter for the SDR dongle, inspired from many articles, but not a copy. I always put the dual gate MOSFET BF998 with the S at the ground and the D in a series 2.2 KΩ plus 1 mH molded shock. The BF998 has a different behaviour than a BF981, and very much different than a 40673.



The values are for the 10 MHz - 30 MHz upconverter. With this upconverter in front the combination SDR dongle + converter is more sensitive than the SONY 7600G - probably somewhere close to 1 micro V. But it has to be adjusted every 500 KHz or so, otherwise the 28.197 MHz beacon is lost .

Final conclusions:

  • The SDR dongle is the cheapest 2 meter receiver a ham radio can buy, and works as a receiver on par with dedicated equipment, which is generally limited by the line of sight, not by sensitivity. A beginner can listen to the weekly nets for some $8–11 CAD, shipping and taxes included.

  • The SDR dongle is the cheapest FM commercial RDS receiver one can have, capable of displaying the digital data continuously transmitted by almost all stations in Vancouver.

  • The SDR dongle was not meant as a general coverage receiver. It was designed as a DVB-T television European standard receiver, and probably it is best for that purpose.

~ Daniel VE7LCG

19/01


Saturday, November 28, 2020

Tech Topics: Review Of An SDR Dongle

The SDR Dongle 

SDR = software defined radio

Having already a conversation with VE7TI (John) about an older generation of SDR dongles I felt compelled to buy a new one, in 2018, a much smaller one, also from China. Most probably what I bought is a knockoff of a NooElec micro dongle. It was in sale at the time, for $7.87 CAD, shipping and taxes included, from aliexpress.com. It came with a remote control, an antenna and a CD with drivers. I discarded all those accessories, which are totally unusable if somebody wants to use the SDR dongle as a general receiver, and not as a DVB-T PC adapter, as intended.

I would like to start my review by underlining exactly that, the SDR dongle I am reviewing was not designed to be a general receiver, as I use it.

My first action was to install it on the computer, on a USB port, and to install drivers and software for it. I followed the instructions from www.rtl-sdr.com. It is tricky to have the drivers work in Windows 10, but if the instructions are followed exactly as in the given website, it works.

Some conclusions

  • The only software that completely works in Windows 10 is SDR sharp. It has various useful plugins, like a plugin for detecting the CTSS tones. Many plugins do not work with the last version of SDR sharp. It is free. A close competitor is HDSDR, which does not know how to decode stereo FM. All other programs I tried partially worked (they do not know all modulations types, have unclear settings, and so on).

  • It has to be connected on the USB computer port with an extender, otherwise the electric noise generated by the computer makes it unusable, completely deaf for useful radio signals. I used my own accessories, in order to adapt the MCX antenna connector from the dongle to my antennas: 

  • Caging the SDR dongle does not help much; if it is not case to case to the electric noise generator, but several centimeters apart, it is fine. I tried to cage it in metal and it did not make any difference in various test situations. I suspect it is already somehow shielded or partly shielded inside.

  • In the commercial FM band it is a cheap stereo and more important, a RDS (radio data system) receiver. It knows how to display the name of the station, the songs that are played at that moment and whatever digital info the station sends in addition to the analog signal. The sensitivity in FM is way worse than 2 microvolts. Any dedicated commercial receiver-amplifier, including my roommate’s Yamaha 2 microV, every single FM radio in the apartment we have, including clock radios, and MP3 portables (the radio part) are more sensitive than the SDR dongle. I am using a proper horizontal dipole antenna on the balcony measuring 71 cm each leg, connected with coax cable to the SDR dongle, while all other 7 receivers have just a small piece of wire as antenna. I estimate the sensitivity in the 88 – 108 MHz band somewhere at 30 microvolts . It is expected the SDR dongle would be less sensitive in the FM band, due to the wide frequency bandwidth. I limited the bandwidth from 250 KHz to 180 KHz and there was a slight improvement.

  • The sound in the FM band is not great. Even at 250 KHz, wide band FM (maximum in SDR sharp program), has audio quality that is just bearable. This is not exactly acceptable. I will not replace any of the radios with this SDR dongle, even though it displays data.

  • The characteristics differ very much on the Rx bands and require adjustment at the RTL dongle settings. That means RF Gain; RTL AGC; Tuner AGC. 

  • It is stable. I did not feel the need for a more stable oscillator. It did require adjustment in the software, 218 ppm as in the above picture for my dongle. This is considered a huge adjustment. I verified this with encapsulated quartz oscillators (32 MHz, 125 MHz, 150 MHz, the 28.197 CW beacon), and indeed it needs that huge adjustment.

  • It seems it does not like the 50 MHz band, and the sensitivity is not great in this band. I confirmed the poor reports as everybody writing about this issue on the Internet experienced the same result, although I hear some local ham radios almost every evening. They never say their callsigns, so I just presume they are ham radios since they are in a ham band.

  • On the 144 MHz band, with a good dipole, it receives everything the Kenwood 7950 and the Chinese walkie-talkie receives. It likes this band and it has a good sensitivity. All repeaters from Victoria, Port Angeles, Nanaimo, and Cowichan are 59. Probably the path is more important than the sensitivity in this case, too. I am at 103 meters above sea level. There are some images for strong local repeaters.
  • It also likes the marine band, air traffic band and the weather band. They are all around 150 MHz and once the settings are done for one station, they can be kept for the weather, marine, 2 meter bands.

  • The CB band and the beacon on 28.197 MHz (VE7MTY, Pitt Meadows, continuous, CW) are in a band where the RTL dongle is not so sensitive. The beacon (nearby me) booms in on my SONY ICF7600G portable radio, with its telescopic antenna. The SDR dongle with a CB whip on the balcony receives it almost OK, but only because I was hunting for the beacon and I knew where it was. The beacon’s signal barely produces a trace in the display spectrum, and I am nearby it (exactly 13.89 km).

  • There are images everywhere. The FM band (88 – 108 MHz) can also be received on 30-50 MHz. The worse thing to do is to use an upconverter, as I saw so many do on the Internet, with a NE612 integrated circuit, and wide non-tuned input. I tried, and the images kill any useful signal. In the end I did 2 converters, in order to cover 3.5 MHz to 30 MHz, one for the lower part and one for the upper part. I used an NE612, attached to an amplifier with a BF998 in front. I have a tuning circuit just at the antenna, and a 2.2K resistor + coil in the output of the BF998’s drain. The source terminal is connected directly at the ground and the BF998 is supplied with 9 Volts (12 V is max in the datasheet, and it does burn after 12 V). The oscillator is an encapsulated 3.3 V powered oscillator, in a socket, to easily change it. The best the dongle worked for me is in the 150 MHz band, to stay away from the FM commercial band and to upconvert the shortwave into a sensitive band that the SDR dongle likes. I can adjust the signal from the oscillator to the value from the NE612 datasheet, but it actually does not make any difference, even if it is attached with 2 Volts (NE612 has a buffer in it before the mixer).


  • The noise of the first element in the SDR dongle must be better than that in the  BFR91A. I tried a wide range untuned amplifier with one BFR91A, and it did not bring anything new, just noise. 

  • The situation changed when I put a SAW 88 – 108 MHz (3 pin filter) in front of the BFR91A, and it helped.

  • It does not run hot. Whatever other users noticed with old SDR dongles is no longer an issue with my 2018 SDR small dongle.

Final conclusions

  • The SDR dongle is the cheapest 2 meter receiver a Ham can buy, and works as receiver on par with dedicated equipment, which is generally limited by line of sight, not by sensitivity. A beginner can listen to the weekly nets for some $8–11 CAD, shipping and taxes included.

  • The SDR dongle is the cheapest FM commercial RDS receiver one can have, capable of displaying the digital data continuously and transmitted by almost all stations in Vancouver. 

  • The SDR dongle was not meant as a general coverage receiver. It was designed as a DVB-T television European standard receiver, and it is probably better for that purpose.



A Postscript…

In the NI Multisim schematic you see a LED with a big resistor in series. It is not a mistake.

All LEDs I use are from China. The 3 mm ones I bought extremely cheap (I think they were 200 or 500 in the bag). The white ones are the most sensitive, and light at several microamps. I need to use resistors between 150 K (for BLUE) and 300 K (for WHITE) in series with the LEDs for 12 Volts power supply.

Now I understand what kind of LEDs they use in the portable lit antennas for walkie-talkies they sell for Baofeng. They light OK. Smaller resistances means burned LEDs. I tried the old values from various published schematics, and NO, they are not OK for the bags of LEDs I have.

~ Daniel VE7LCG

18/12


Saturday, October 31, 2020

The November-December 2020 Communicator

 

Over 110 Pages Of Projects, News, Views and Reviews... 

Read in over 120 countries now, we bring you 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:  


https://bit.ly/SARC20NovDec



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



Wednesday, October 28, 2020

Not All Triplexers Are Equal: A Review of the Dunestar HF Triplexer

 

...Buyer Beware!

I had an opportunity to troubleshoot and repair SARC’s Dunestar triplexers. A couple of surface mount capacitors failed and had to be replaced. The triplexers are now in working order again. But...

These triplexers were very cheaply made. They contain only resonant circuits instead of filters. Better diplexers have low pass filters, band pass filters and high pass filters. So why are filters better than resonant circuit? Let’s see:


Here is a schematic diagram of our triplexer . There are 3 resonant circuits, one for 160, one for 80m and one for 40m. 

The frequency response curve of resonant circuits is narrow and may not cover a whole amateur radio band. In the case of our triplexer, the 80m bandpass is so narrow that does not cover both the CW and SSB portion of the bands. There is a jumper JP that adds more capacitance (C3) for the CW band by lowering the resonant frequency. Without the jumper the circuit is tuned to the SSB band. However, the jumper is located inside of the enclosure and it is very inconvenient to change.


Below are the 80m band graphs showing insertion loss (G) and VSWR of our Dunestar triplexer, with the jumper in the SSB position. As you can see it is useable only from 3.685 to 3.882 MHz if the practical VSWR limit is 2.  It would be slightly wider if the allowable SWR is 3, but it still covers only the centre of the band.


Triplexers which use filters (low, high, band pass) are much better. Below is a schematic diagram of a more sophisticated triplexer using filters rather than resonant circuits.




Let’s examine the characteristics of this 80 MHz bandpass filter. The graphs [above] show the scans taken the same way as for the Dunestar units. You can see that the band pass filter is flat and covers the entire 80m band (from 3.42 to 4.10 MHz) CW and SSB without need of a jumper. The low pass and high pass filters have similar characteristics; they are flat and cover the entire 160m and 40m bands.

So what have we learned here?

First, you get what you pay for.

Second, you have to be careful using this triplexer because outside the narrow pass bands you will run into high VSWR. It is worthwhile to check the specifications before you purchase any triplexer. 

As with any triplexer, you need to use extra band pass filters (one per band) because the isolation between the inputs is not sufficient (for example some RF power from the 80m transmitter could get into 40m receiver and damage the receiver’s front end).


~ Les Tocko VA7OM


18/12





CQ CQ CQ

The January-February 2021 Communicator

110 Pages Of Projects, News, Views and Reviews...  Happy New Year! The first issue of The Communicator magazine for 2021 is now available fo...

The Most Viewed...