Happy Podcast Day! Caveat Emptor!

Today is Happy Podcast Day and a large Tip of the Cap to N2CQR who has had the SolderSmoke Podcast for over 2o years. Bravo Bill, and you can acclaim being on the leading edge with this media communication forum about our wonderful hobby. It has been a honor to ride along with you for a small portion of those 20 years!

This is a Pixie CW Transceiver and certainly can be had at low cost but not at Walmart.com. I was surprised to find out Walmart sells ham gear.

Pixie S but not at Walmart.com 

Having few parts and a PCB it should appeal to our demographic. It is low cost too! 

Basically, it is a kit comprised of two transistors and an IC plus a crystal for operation on 40M. A Crystal Oscillator runs all of the time to supply an LO on receive to a detector as you would have in a Direct Conversion Receiver. Upon keying the circuit, you get a substantial power Output from the second transistor. The downside is no QSY as such and you have but a single frequency radio. 

Worldwide expert homebrewer Peter Parker, VK3YE says the following about the Pixie.

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The biggest selling (but not necessarily most commonly heard!) QRP transceiver kit would be the Pixie and its variants. Costing less than a takeaway burger meal, it's the cheapest transceiver kit available. The transmitter puts out a few hundred milliwatts CW on a single crystal-controlled frequency (often 7.023 MHz). The receiver is direct conversion with little selectivity. Performance could charitably be described as 'basic' but the design is ingenious, with many parts shared between the transmitter and receiver.

The first question to ask is whether you can make contacts with such a simple affair. The answer is 'yes', with hard work. I class the Pixie as a novelty project, purchased more for the fun of construction than its operating capability. However, if you're persistent, have a resilient sending wrist (for all the calling you'll do) and connect it to a full-sized outdoor antenna then you will work stations hundreds of kilometers away.

So how does the Pixie work? One transistor is connected as a 7 MHz crystal oscillator. It is continuously on, to generate the carrier on transmit and to provide the local oscillator for the direct conversion receiver. The second transistor is the RF final amplifier on transmit. On receiver it operates as a crude detector for the direct conversion receiver. The audio signal at the output of the detector is very low which is why the LM386 audio stage is there to provide some amplification. This is the only stage that operates on receive only.

Other parts of the circuit include the pi-network low pass filter and the transmit/receive frequency offset. The latter is required in all direct conversion CW transceivers and ensures that the transmitter carrier and receiver local oscillator frequency are slightly different so that incoming signals produce an audible beat note in the receiver...

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If you click on the Pixie CW Transceiver link (earlier in the blog) you will see a you tube video that evaluates this kit. It doesn't do very well and with 5 Volts PTP output that amounts to 62.5 milliwatts. You should be able to see about 10 Volts PTP which now gives you 250 Milliwatts.

While the ham in the video has some really uptown test gear, I am not sure what he saw is accurately reported. I did not see if he had a dummy load connected when he put the scope on the output. I hope his scope is not the dummy load. The output looked pretty crappy. 

For those who have built Regen Receivers you likely are aware they can actually generate RF into the antenna on receive. In fact, the spy operators in WWII using a Paraset had to be cautious of this issue on receive as they could get tracked down.

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Radiation of RF from Regenerative Receivers

The radiation of RF from regenerative receivers is a significant aspect of their operation. Regenerative receivers utilize positive feedback to amplify the RF signal, which can lead to oscillation and subsequent radiation of RF energy. This radiation can occur when the feedback loop is not properly controlled, causing the receiver to oscillate and produce unwanted RF emissions. To prevent this, regenerative receivers are designed with various mechanisms to prevent free oscillation and ensure efficient operation. These mechanisms include the use of variable condensers, tickler coils, and other components that help maintain the receiver's stability and reduce the risk of radiation. 

njarc.org+5

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The receive RF signal at the antenna in the video may be a similar issue with the Pixie. 

A real value in the Pixie is to have fun with your "friends". Buy a Pixie for a friend and enjoy the angst they encounter as they try to make it work. I think the video presenter mentions that two other friends have built the kit and saw the same poor results.

The seven-word economic law is at work here:

Them has gets ain't no free lunches. Why do you think the real QRP CW transceivers cost more... because they work. Better yet roll your own DCR and buy a Tuna Tin Two kit from W1REX.

Them that know can make it go. Caveat Emptor!

73's

Pete N6QW