Re: WX & Other thoughts...


Jerry Haigwood <jerry@...>
 

Hi Dan,
    I have looked at Farhan's Minima transceiver.  As is, I doubt if the transceiver will put out more than a few microwatts.  If you look at the design, the transmitter has only 1/2 of a bidirectional amp using a 2N2222 as an output before going through the crystal filter.  Crystal filters cannot handle more than about -10 dbm before being overdriven and subject to failure.  I asked Farhan about the amount of drive going through the crystal filter and he stated it was about 200mV in and about 50 mV out.  He didn't state if that was RMS, Peak or Peak-to-Peak.  If we give him the benefit of the doubt and call it RMS, then coming out of the crystal filter is 50 microwatts (assumes a 50 ohm load).  After the crystal filter, the only active device is the mixer.  Something is amiss here.  I suspect Farhan meant to say that he can get 1 watt out of the JBOT amp with the Minima driving it.  To get up to 5 watts, another stage of amplification will be needed.  You will also need a low pass filter after the JBOT amp.
Jerry W5JH
"building something without experimenting is just solder practice"
 

 
 

On Wednesday, January 22, 2014, <on30ng@...> wrote:
 

Been cold in beautiful central IL. I just looked and we're having a heat wave - 13 F! We still have snow on the ground. Sure has been a weird winter. I don't remember this much snow since I was a kid. We have a lake in Decatur and as a kid I remember people used to drive on it in the winter. Recent years that wouldn't work so well.


Has anyone heard about Farhan's new transceiver design? (Farhan developed the marvelous BITX transceiver)
It uses an Arduino for some general functions, and to drive an Si570. He uses the KISS mixer and drives it straight from the bandpass filters with no RF amp. CW/SSB and all HF. Real unusual tuning control. Instead of a encoder he uses a 100K pot. From the 'center' you tun the pot left to go down in frequency and right to go up in frequency but like a jog/shuttle knob on a VCR the further you turn from center the faster the frequency moves. A little unusual but should work. 
As-is the XCVR puts out 1 watt but Farhan also has a nice amp called the JBOT (just a bunch of transistors) that can up it a bit. 
All open source like. 
After I get my G-59 going I plan to try to build one. Only expensive part is the Si570. I see Si no longer allows you samples! :-)

73
Dan - KB9JLO
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QRP....."more smiles per watt"

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