First Prototype Transmitter Board

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NZ0I

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Mar 1, 2019, 8:36:40 PM3/1/19
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The first complete prototype transmitter board has been built and tested along with the first prototype power supply board. Some modifications were required to make it work correctly, and the effort revealed numerous improvements that will go into the next prototype version. Here's what the first prototype boards were ultimately able to do:

80m Transmitter
o 10mW to 1.5 watts of output power
o The signal meets FCC spectral purity requirements
o Parts count was minimized to just 3 active components: SI5351 clock generator, FET driver, and a power FET.
o Transmitter can operate in continuous transmit (at room temp) without any components getting more than slightly warm.

2m Transmitter
o 10mW to 170mW of output power
o The signal meets FCC spectral purity requirements
o Transmitter can operate in continuous transmit (at room temp) without any components getting more than slightly warm.

Power 
o Total battery current can be dropped below 300uA when the transmitter is shut down and the processor is in sleep mode

Changes to the 2m transmitter design are in the works that should bring the total output power above 250 mW.

A picture of the complete transmitter, minus box, has been added to the web site. 


Gerald Boyd

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Mar 4, 2019, 8:24:24 AM3/4/19
to NZ0I, Receiver Development Platform
Charles,
Nice work 
Jerry 

Sent from my iPhone
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NZ0I

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Mar 4, 2019, 5:19:15 PM3/4/19
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I looked into several approaches for increasing the 2m transmit power. What I wanted was a VHF/UHF power amplifier component with internally-matched 50-ohm input and output, requiring a single power supply voltage and only a few additional parts. I actually found a few parts meeting all requirements, but the price tag was upward of $150 per part! Forget that. Then I came across the following:


It isn't cheap at $15 each, but it is in the ballpark. It requires a negative power supply, but at low current, so that requirement only adds a few more dollars and cm^2 of board space. It doesn't require any impedance matching when operating at 146MHz, and it can deliver up to 1 Watt of power. So that's what the next design will use. The new schematic, BOM, and boards can be found at the bottom of the project web page: https://openardf.org/index.php/ardf-open-equipment-project/open-dual-band-ardf-transmitter/

-Charles 


On Monday, March 4, 2019 at 8:24:24 AM UTC-5, Gerald Boyd wrote:
Charles,
Nice work 
Jerry 

Sent from my iPhone

On Mar 1, 2019, at 6:36 PM, NZ0I wrote:

The first complete prototype transmitter board has been built and tested along with the first prototype power supply board. Some modifications were required to make it work correctly, and the effort revealed numerous improvements that will go into the next prototype version. Here's what the first prototype boards were ultimately able to do:

80m Transmitter
o 10mW to 1.5 watts of output power
o The signal meets FCC spectral purity requirements
o Parts count was minimized to just 3 active components: SI5351 clock generator, FET driver, and a power FET.
o Transmitter can operate in continuous transmit (at room temp) without any components getting more than slightly warm.

2m Transmitter
o 10mW to 170mW of output power
o The signal meets FCC spectral purity requirements
o Transmitter can operate in continuous transmit (at room temp) without any components getting more than slightly warm.

Power 
o Total battery current can be dropped below 300uA when the transmitter is shut down and the processor is in sleep mode

Changes to the 2m transmitter design are in the works that should bring the total output power above 250 mW.

A picture of the complete transmitter, minus box, has been added to the web site. 


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