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public:radio:topics:arduino:qrss_tx [12/07/26 07:55 BST] – johnpublic:radio:topics:arduino:qrss_tx [12/07/26 16:39 BST] (current) – [Test Amp] john
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-====== QRSS TX ======+====== QRSS MEPT ======
  
-I started work on my small QRSS TX idea with a simple Arduino / SI5351 / 16x2 LCD arrangement.+I started work on my small QRSS MEPT idea with a simple Arduino / SI5351 / 16x2 LCD arrangement. The LCD is only there because I found this breadboard setup already with Seeeduino Nano, SI5351 and LCD in my box of "Arduino Project bits" - from a previous experiment - and I thought I'd keep it for the time being as a display to help in debugging (?). Once the MEPT is functional and ready for operation I'll remove the LCD (and its code from the sketch)
  
 {{:public:radio:topics:arduino:qrss_1.jpg?direct&600|}} {{:public:radio:topics:arduino:qrss_1.jpg?direct&600|}}
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 {{:public:radio:topics:arduino:gm4slv_test_tx1.jpg?direct&600|}} {{:public:radio:topics:arduino:gm4slv_test_tx1.jpg?direct&600|}}
  
-The sketch+==== The sketch ==== 
 + 
 +++++ Click to read / hide | 
  
 <code c> <code c>
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 volatile long freq = 10139780;  //       volatile long freq = 10139780;  //      
-volatile long oldfreq = 0; 
-volatile long currentfreq = 0; 
  
 int digit0 = 0; int digit0 = 0;
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 </code> </code>
  
 +++++
  
 +===== Step Two =====
  
 +The next step will be to build a small TX PA to boost the SI5351 output up to around 1W and a LPF. I'll add a PTT line to key the PA, driven from the Arduino so that the sketch can have periods of carrier off between cycles if necessary. 1W should be enough power and should be simple enough to generate. I might have a go at a Class-E MOSFET amplifier.
  
 +FIXME
  
  
 +==== Test Amp ====
 +
 +I found a 30m PA strip from a previous project that produces about 6W from < 10mV drive, with 3 class-A bipolar driver stages feeding an IRF510 MOSFET - originally intended as a linear amplifier.
 +
 +I've played with the supply volts and the MOSFET bias and can comfortably get up to 3W carrier with 8V supply. It's not terribly efficient but at QRP levels that's hardly relevant.
 +
 +I've got it connected to the Ardiuno/Si5351 and it's on the air running 1W. 
 +
 +{{:public:radio:topics:arduino:mept_1.jpg?direct&600|}}
 +
 +{{:public:radio:topics:arduino:mept_2.jpg?direct&600|}}
 +
 +{{:public:radio:topics:arduino:mept_3.jpg?direct&600|}}
 +
 +I'll use this amp as a blueprint for a new PA for the MEPT, perhaps with fewer stages as I don't need so much gain or linearity.
 +
 +I've seen it on grabbers around Europe 
 +
 +=== Grabber results at 1W ===
 +
 +
 +{{:public:radio:topics:arduino:m0mqw.jpg?direct&600| M0MQW}}
 +
 +{{:public:radio:topics:arduino:sa6bss.jpg?direct&600|SA6BSS}}
 +
 +{{:public:radio:topics:arduino:so5cw.png?direct&600|SO5CW}}
 +
 +At 1533z I reduced power to around 200mW 
 +
 +=== Grabber Results at 200mW ===
 +
 +FIXME
 +
 +
 +===== Stretch Goals =====
 +
 +  * Add a function to generate "Slow FSK Hell" to make waterfall-readable text - see the image of **GM4GHK** below
 +  * Add DFCW
 +  * Add a "normal-speed CW ident" for cases where it might make sense (?)
 +
 +{{:public:radio:topics:arduino:gm4gkh_hell.jpg?direct&600|}}
 ===== Further Information ===== ===== Further Information =====
  
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 Page updated : ~~LASTMOD~~ Page updated : ~~LASTMOD~~
  
-{{tag>}} +{{tag>radio qrss arduino mept}}
  
 +~~DISCUSSION~~