While I was away on my honeymoon, I noticed that the upcoming kit that I’ve been hinting about for months has finally been released. The Four State QRP Group announced availability of the VRX-1 direct conversion receiver. The VRX-1 is a simple 40 meter VXO-tuned receiver (crystal on 7.030 MHz), but it’s not your typical NE602/LM386 combo. The product detector consists of only a 2N7000 MOSFET, a capacitor, and an inductor. The audio amplifier is a TDA7052 from NXP. This little 8-pin DIP can output 1 watt of clean audio into low impedance headphones or a small speaker. Current consumption is only about 40 mA, which makes the VRX-1 easy on your batteries if you take it out for portable use. The construction of the receiver is done Manhattan-style, but don’t let that put you off if you’ve never built this way before. I provide a precise, detailed layout diagram to show you exactly where each part is placed and how it is oriented. There’s also some very detailed build documentation to walk you through the build, which you can preview at the VRX-1 web page. Even the novice builder can construct this radio!
The VRX-1 was designed to be a companion to the NS-40, or other similar rock-bound 40 meter QRP transmitters. I also include instructions on how to use some of your own parts to modify the VRX-1 for operation on any HF band, so don’t feel like you are stuck on 40 meters if you would like to try to experiment a little. In a future blog post, I’ll walk you through the process of integrating the VRX-1 with a standalone QRP transmitter to make a complete station.
Proceeds from the kit sales go to fund OzarkCon 2010; I don’t make a dime off of it (just the glory, LOL!). So please support the QRP community and try your hand at a new kind of kit. It’s only $25 postage paid in the States, $28 for DX.
Hi
I am thinking of building a vrx1 work a like from my junkbox. Is it ok to use standard jfet for the mixer. The only part I have is a bf245. What are the biasing requirements and LO power requirements for the vrx1?
Fernan, yes a JFET should work fine. I based my mixer off of the work of KK7B, who wrote a white paper on the subject for his class at Portland State University. In that paper he describes the mixer using a J310 JFET. The main thing is that you will have to negatively bias the gate, so he uses self-biasing on the source to accomplish it. Here’s the link:
http://web.cecs.pdx.edu/~campbell/mixnotes.pdf
LO power levels are not critical since the gate of the FET has a high impedance. I recommend a LO voltage of about 5 Vpp for best conversion gain, but you can get by with quite a bit less.
Good luck and let me know how it works!