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Author Topic: $3 to Quintuple the Output Power of a 40 M Pixie Transceive  (Read 4254 times)

KD6RF

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$3 to Quintuple the Output Power of a 40 M Pixie Transceive
« on: January 16, 2017, 08:19:04 AM »

The Pixie is a fun and popular QRP transceiver kit. However, typical output power on 40 M is only about 300 to 500 milli-Watts – a bit too QRPp at times…

The article shows cheap and easy ways to pump up the output power to around 1.6 or over 2 Watts, depending upon the power supply type - One is to swap out the final amplifier transistor and adjust matching, and the other is to bypass the bridge rectifier on those units that use one ===> http://vtenn.com/Blog/?p=1348

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VTenn Antennas
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AC6AN

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RE: $3 to Quintuple the Output Power of a 40 M Pixie Transceive
« Reply #1 on: January 16, 2017, 02:39:18 PM »

That is a cute idea but to benefit from it you'll have to hear better first...
The Pixie receiver gain is just about the gain from the LM386 which is not much.
You know what they say, if you can't hear them you can't work them. :(
A 5532 dual opamp can replace the LM386.
First stage is a gain/bandpass filter and second stage a gain/lowpass that can drive headphones.
There are numerous examples of this circuit in a QRP kit.
The cost should be around $1 with a little "dead bug" assembly.
The Chinese outfits can probably implement all these mods for $5 shipped... ;
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KD6RF

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RE: $3 to Quintuple the Output Power of a 40 M Pixie Transceive
« Reply #2 on: January 18, 2017, 04:24:08 AM »

I'm finding exactly what you said by using the units in the real world :)  

Comparing it to the Icom home rig, It needs about 30 dB more gain to drive a speaker, perhaps 10 or 15 dB to be comfortably audible in headphones down to the typical noise floor.  

Even then, it's going to the crappiest of all possible receiver architectures - but still usable and fun to mess with.

It is the lowest current draw of the rigs I have at about 15 mA on RX...




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VK3YE

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RE: $3 to Quintuple the Output Power of a 40 M Pixie Transceive
« Reply #3 on: January 18, 2017, 04:34:12 AM »


It is the lowest current draw of the rigs I have at about 15 mA on RX...

15mA is pretty good but lower is possible.  A good earphone driving regen can draw under 3mA

https://www.youtube.com/watch?v=GJBRIf5Xkzw

Mods to Pixies are fun projects and I've done a few.  But it's also a bit like putting lipstick on a pig - if you want a good 'contact getter' I'd be inclined to start with scratch with something that has none of Pixie's vices. 
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Peter VK3YE/AK3YE    Youtube videos at VK3YE

Author of 'Minimum QRP', 'Hand-carried QRP Antennas', 'Ham Radio Get Started' and other popular books on ham radio.
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AC6AN

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RE: $3 to Quintuple the Output Power of a 40 M Pixie Transceive
« Reply #4 on: January 18, 2017, 12:02:46 PM »

Peter, that 3mA will not handle much dynamic range...
We're talking a contest Pixie... hi hi
It's sure cool though! ;D

Some Motorola HT shared current between two circuits in series, each running at half the supply voltage.
Maybe combining such features can net an even thriftier receiver...

There is also a lot of talk about energy harvesting.
One interesting circuit from the 60's was rectifying energy from a local AM station to be used as a supply for receiving another station. I don't remember if that was one or two transistor design... Zero power (not really, but close to it)!
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