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U2 Final Voltage
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"Paul KE7HR"
My U2 was putting just over 12 volts peak to peak into 50 ohms on 80 meters using a 5 volt final drive (LM2596 switching regulator) with one final. I installed the other two finals and only got an increase of 1 volt peak to peak (about 60 mW increase). I put the full battery voltage to the finals (12.6 volts) and now get just over 30 volts peak to peak or about 2.25 watts. Since the BS170 is only rated at 350 mW I will next start cutting down the voltage to the finals with another regulator to get the power down to about 1 watt.
What are others with the three finals running for voltages? I have run a couple of nights with the 12 volts final voltage on WSPR with the devices touching a nice big piece of aluminum. A better, field portable, type of heat sink will be worked out... For other modes with 100% transmit, I would really not recommend pushing the devices this hard. Screen shots from the oscilloscope of the voltages into 50 ohms in the photos section. KE7HR |
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"Dave"
Paul
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I was running a matched set of 3 Fairchild transistors and they are rated for 830 ma max and can take quite a bit of heat max 150c which should put over 2 watts out. I am using a small wattmeter and with 9 volts to the pa I can get 1.2 watts out on 30m Dave --- In QRPLabs@..., "Paul KE7HR" <ke7hr@...> wrote:
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"Dave"
Sorry that should be 830 mw max dissipation on the bs180 to-92
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Dave --- In QRPLabs@..., "Paul KE7HR" <ke7hr@...> wrote:
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"Paul KE7HR"
Thanks, Dave. I have a bag of BS170 and don't see marks to identify the maker... I put a heatsink on for good measure and also a variable PA supply separate from the supply that feeds the board. Now everything runs quite cool, even at the full 12 volts. I have reduced the output to 1 watt (20 vpp into 50 ohms) and it should now run ice cold even with high duty cycle.
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I ran a test from 5 volts up to almost 12 volts (the variable supply needs 1.5 volts or so for regulation) and built a chart. The result is in the Files section, if anyone wants to look at the output vs. supply voltage for 80 meters. The output was sent to a dummy load and the voltage across the load was measured with an oscilloscope. I also put several photos in the KE7HR folder that show the U2 in a box with a homebuilt heatsink. It is just about ready for the backpack... KE7HR Paul in Phoenix, AZ --- In QRPLabs@..., "Dave" <airdry@...> wrote:
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"Yannick"
Hi,
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I have not checked the topology chosen by Hans for the PA and this is just for comparison. With the KD1JV ATS/MTR series of transceivers, we achieved 5W from 3 Bs170 at 12V on 20 meters CW. Power drops to around 3W at 9V. They are happy at 12V not getting hot if run to a 50 ohm load. However the are getting touchy if the impedance goes too low and keeping them at 10V makes the PA sturdier. The highest frequency achieved with the ATS/MTR is 15 meters, but I am not sure this limit comes from a restriction in the PA. Overall this is more a design choice and the main limit being the power consumption of the DDS in receive mode. These are rigs to bring in SOTA expedition and must be small and use as little as possible power from batteries. I repeat this if is for CW and I guess for continuous transmission I would not go above 1W. Last thing, the ATS/MTR series use a MSP430 micro-controller. I have started to modify KD1JV code to turn the MTR into a QRSS beacon. However it is such a good transceiver and buying one is so hard that I finally built my own QRSS/WSPR DDS beacon design... 73, Yan. --- Yannick DEVOS - XV4Y --- In QRPLabs@..., "andyfoad@..." <andyfoad@...> wrote:
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