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August 9th, 2024. Initial work on the CW Transmitter portion of the CW Transceiver

I am having great fun looking at some transmitter topologies that indeed have some added twists. Several years ago, I purchased some Russian PNP HF Germanium Transistors. I got one hundred pieces for about $2o. They look funny and the pinout is a bit strange, but they work. 


I have working a 20M Crystal oscillator on 14.060 MHz and it produces about 0.8 Volts PTP into a 50 Ohm load (1.6 Milliwatts). I also built a Driver stage using a 2N2907 that by design should produce 60 milliwatts output from the 1.6 Milliwatt input. A second stage with an IRF510 should push us close to 1 watt output. Might even try the P type MOSFET equivalent of the IRF510. See the April 16, 2024, Blog posting on the LT Spice simulation and the Part Number.


800 mv PTP = 1.6 milliwatt



Russian PNP Germanium Top Hat Transistor at 14.060MHz

Small steps here. I want to use the crystal oscillator initially as the RF Source and get that nailed down and working as a full transmitter. Then I will switch to the Si5351. Note only one transistor is used in the oscillator and the second one floating there is just a spare device. 

Below you can see the pads for the BPF ready to be populated. The output with the Driver stage looks like this in hardware and a plot of the output.


2N2907 PNP Driver Stage = 58 Milliwatts

4.8 Volts PTP = 58 Milliwatts



The plan is to use a keying transistor to key the 2N2907 Driver/Buffer stage. The 2N2907 is producing about 15.6 dB of gain and the LT Spice predicts about 16+ dB of gain. Kind of like Mary Jo in the backseat of the 57 VW Beetle --- everyone has a wicked smile on their face!

The math says 10*log (58/1.6) = 15.59 dB which is close to the 2N2907 design. Now for the sanity check on the IRF510 we have 10*log (1000/58) =12.4 dB which is in the range of gain figures for the IRF510.

There is no reason why PNP transistors can't be used for the transmitter and that is the plan. BTW the 2N2907 has a device dissipation of 600 milliwatts and an Ft of 200 MHz. It is loafing along!

This just showed up on my phone a new R Pi4 variant, the Model B. The 2GB version available from Digi Key is only $45. My remote operating HL2 radio uses the R Pi 4 (plain) and works FB.


TYGNYBNT

73's
Pete N6QW

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