Ham radio TV show

 

http://youtu.be/Ia5TeYPdwbY

Testing “generic” MOSFETS for RF PA use

Testing “generic” MOSFETS for RF PA use

Earl, 4Z4TJ / VA6TJ

Low cost plastic MOSFET transistors can be used to make effective low power HF PAs.  I have an amplifier I made with IRF510’s that effectively brings a Softrock transceiver output up to legal QRP (5 W out) with a 15 volt power supply.  With that experience in mind, I started looking for plastic MOSFETs that were actually designed as RF amplifiers, and not as components in a switching power supply.

A while ago I bought some supposed RF MOSFETS on eBay from a supplier in China.  I did not take sufficient care in checking out the history of the parts that are marked MS1307 from International Rectifier.  A bit of Googling around showed that IR never made a transistor designated MS1307.

I decided that the transistors needed to be tested under actual RF amplification conditions, and not just with a multi-meter.  Therefore I build up a simple test circuit,  based on a 40m CW xmtr by VA3IUL, where I could plug in a MOSFET and test it as a 40m amplifier.   The transistor socket was taken from the wiring harness of a discarded ATX computer power supply.  The source of Q2 (tied to the emitter of Q1) needs to be grounded to obtain output – this is where the CW key would be attached, or in my case I soldered in a micro switch.

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0.5 W out into 50 ohm load through LPF (5 v/division;  10 V P-P).  Supply voltage = ~12 V

 

Initial results can be seen from the photos on the previous page.  The transistors do amplify in this circuit and I can get a nice waveform if I adjust the gate bias (R5) voltage to give a maximum 1 W output into 50 ohms.  Adjusting the bias to exceed this power level causes the scope trace to turn ugly showing that bias has shifted the transistor off the linear portion of its load-line.   What needs to be done to determine the operating limits is to vary the input level to the MOSFET gate while maintaining the bias so the transistor is operating in its range and at different supply voltages.  This is a good reason to buy a nice signal generator  J

With the simple setup shown in the schematic at a supply voltage of 13.6V, PA voltage gain as measured with the scope probe, was determined to be approximately 15 db.  Vin = 4 V P-P and Vout into 50 ohms = ~25 V P-P.

After this test, I thought about improving the impedance match into the MOSFET gate and buffering the output of the crystal oscillator.  I adapted a section of a circuit from one of my Softrock transmitters and came up with this:

This circuit did not do much to improve the waveform going into the gate of the MOSFET but it did permit higher output power with a nice sine wave after the LPF.  I could easily obtain  1.5 W out with a 13.6 V supply and a MOSFET gate bias voltage of 4.0-4.1 V (measured with open source).

 

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I also tried reducing the bias on the oscillator transistor Q1 base by lowering the value of the base to ground resistor to about 2/3 the original value.  This did not have any noticeable effect.

 

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Breadboard with the added buffer amplifier and 9:1 input transformer to the MOSFET gate

 

I do not consider this circuit to be a useable transmitter.  It’s a test jig for performing  a rudimentary check on RF MOSFETs or picking a matched pair.   As a transmitter the circuit is not appropriate: the leads are too long; there is no thermal protection in the bias, etc.  For these reasons I am not going to invest effort in testing at a higher frequency.    However, I did listen to the 7.3 MHz output (into a dummy load) on the station transceiver and, in fact, the CW sounded just fine, no key clicks, shifting notes or other QSD.

After a suitable number of cups of coffee the next morning, I realized that L1, R6 and C2 are to zero beat (pull) the crystal frequency when operating CW and are not needed for a test jig.  If you remove them, it may be necessary to increase the value of C1 .

 

 

 

Planned improvements:

  1.  Add an ammeter to be able to determine DC efficiency.
  2. Regulate the bias voltage supply.
  3. Compare RF amp results using different switching power supply transistors
  4. Determine the effect of increasing the supply voltage to 24 V.

 

I recommend checking out VA3IUL’s website http://www.qsl.net/va3iul/ where there are many circuits and ideas for projects.  Thanks to Iulian for his assistance with this little project.

 

Earl, 4Z4TJ / VA6TJ

thingCharger

Cool thing

http://thch.us/5943138

New Canadian Band Available

RAC Notification:
RADIO AMATEURS OF/DU CANADA applauds 60 meter band frequency allocations!
RAC has been working on achieving this new band allocation since 2010.
Industry Canada has announced that a number of specific frequencies within the 60 meter high frequency band have been approved for amateur radio use as RAC advocated. This is now in effect.
A total of five specific frequencies within the 5 MHZ band have been allocated, 5332 kHz, 5348 kHz, 5358.5 kHz, 5373 kHz and 5405 kHz. Radio amateurs across Canada have new frequencies to explore as a result of a recent decision of Industry Canada.
“Canada has joined a number of countries in making channels available in the 60 metre band, near 5MHz for use by radio amateurs. This will provide increased ability for Canadian radio amateurs to help out in providing emergency communications when existing systems fail as has happened in ice storms and flooding. We applaud this decision of the Canadian government.” said Geoff Bawden, President of Radio Amateurs of Canada.
Unlike the commercial communications systems so important to modern society, amateur radio does not require an extensive infrastructure for communications. Radio amateurs take advantage of natural phenomena to send their signals across town and around the world. They delight in being able to set up in a remote location with their own power supplies and simple antennas, often home built, competing to see who can make the most contacts in a limited time. The Amateur Radio Emergency Service in Canada, sponsored by RAC, provides training and organizes exercises for radio amateurs to sharpen their skills to be able to respond to emergencies. As well these organizations and amateur radio clubs often provide communications to community public service activities and events such as ski races and marathons, bicycle races and car rallies. The skills radio amateurs develop through their hobby and these activities mean that in emergencies that shut down power grids, internet and wireless communications, amateur radio can continue to function. In major emergencies such as the earthquake and tsunami in Japan in 2011 and the Typhoon Haiyan in the Philippines last year amateur radio operators are often the first source of information from affected areas.
The key resource for amateur radio is access to the radio spectrum. Conditions in the atmosphere and high in the ionosphere determine the distances over which communications are possible. The new allocation at 60m between existing allocations at 80 m and 40m should make regional communications more reliable. Furthermore as Canada and the United States have allocated many of the same channels to their radio amateurs cross border communications are possible. Fortunately major emergencies are relatively rare. Radio amateurs will explore communications on the new frequencies as they do in all available bands, experimenting, learning and making new friends across the world.
TECH DETAILS
The five 60 metre channel allocations are the same as authorized in the USA, with the same power restriction of 100 watts ERP (relative to a dipole antenna). Transmissions, independent of emission mode, must be centered on the each of the following frequencies: 5.332, 5.348, 5.3585, 5.373, and 5.405 MHz with a maximum allowable channel bandwidth of 2.8 kHz. When operating SSB, upper sideband will be the convention to follow on the 60 metre band. Other modes that are permissible will be CW, Data (including PSK 31 and Pactor III), and RTTY. With this latest authorization on operation on the 5 MHz channels to Canadian Amateurs with HF privileges, there will no longer be a requirement to operate under a special Developmental license and VX9 call sign. Holders of such licences can now let them lapse. Canadian amateurs should refer to the posting of RBR-4, Issue 2, for all details before proceeding to operate on the new 60 metre channels: http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10650.html (copy the link to your browser)
Their curiosity and eagerness to develop and share this hobby will enrich the communities where they operate and provide needed resilience in communications when emergencies require it.
Technical details of this decision can be found here: http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10623.htm (copy the link to your browser)
Tech/Admin contributions, Norm Rashleigh VE3LC. Glenn MacDonell VE3XRA.

thingCharger Neat Idea

This is a cool device.

http://thch.us/5943138

Humpback whale foundation called Juniper Foundation

Post from Brian Davies from down under
20 m beacon
Last year I learned about the humpback whale foundation called Juniper Foundation in Hawaii. They have deployed hydrophones on “wave gliders” see link http://www.jupiterfoundation.org/projects.shtml
One of these is a beacon at 14.070
Happy New Year
Brian
 
Thanks
73 to all….+31 on xmas day we swam in the ocean morning and afternoon.

CAARC Christmas Pot Luck Supper

The CAARC Christmas Pot Luck Supper was enjoyed by approximately 35 guests on Sunday December 1. Thanks to everyone who attended and brought such good food. The following great pictures are provided by Karen VA6LDY, thanks Karen.IMG_3260IMG_3262IMG_3263IMG_3264IMG_3265IMG_3266IMG_3267IMG_3270IMG_3272

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IMG_3275IMG_3278IMG_3279IMG_3280IMG_3281IMG_3282IMG_3258IMG_3259IMG_3255IMG_3254IMG_3253IMG_3251

IMG_3250

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Free HandHeld winner

 

         The draw for the Free Hand Held at the Annual General meeting was won by a new ham to the Red Deer area.     Congratulations to Steve GW7GCD and we welcome him  and his wife Maria to the area.

End Fed Antenna by MOSHE INGER 4Z1PF HaGal Israel Amateur Radio Club Magazine

End Fed Antenna by MOSHE INGER 4Z1PF HaGal Israel Amateur Radio Club Magazine, issue 410, June 2013 translated by Earl VA6TJ
What more could we wish for? An easy to build antenna made from inexpensive materials, covering all
the HF bands! The simple end fed antenna described in this article meets these requirements.
A half wave end fed antenna exhibits a high impedance to the transmitter. This mis-match is too high
for most external or internal antenna tuners to deal with. However we can use a transformer to
overcome this mis-match.

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Click this following link to download the rest of the article in PDF format

end fed antenna 4z1pf translation