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This "Eden Project" is an Eden Valley Radio Society project to construct from scratch a 70MHz QRP SSB transceiver.
The SSB is generated using the "filter method" with an IF of 11.0592MHz.
Ron Taylor G4GXO of Cumbria Designs has produced the design for us all to try to replicate and get going.
The three-way header plug nearest to the camera is for the receiver volume control pot.
No PCB has been produced, the objective is to build it from scratch using just PCB laminate.
This is a variation on the "Manhattan" method - IC's and associated components are built on small PCB "pads", with the remainder in a "point-to-point" style.
Some "dead bug" (also known as "Ugly") methodology is no doubt going to creep in here too.
The stages nearly completed so far are the RX product detector (short of its crystal at the moment), the AF pre-amp and the AF output stage.
When these stages are finished, it will be time to put the ICs in their sockets, power up, test and de-bug.
This is the first time I have used this method of construction, and I'm learning as I go - you certainly get very close to the circuit with this method!
Previously projects have used either PCB (pre-manufactured in the case of kits, or occasionally home-made) or Veroboard. I'm not the neatest worker in the world, as you can see!
The empty space at the top is to accommodate the TX modulator (left) and the Mic preamp (right)
There is a photo of Ron presenting his creation at the 2009 G-QRP Club Convention at Rishworth - Rishworth
Please feel free to use this photo but be sure to credit ArmchairBuilder.com and provide this link...
armchairbuilder.com/resources/how-to-build-your-own-home
Thanks,
Michael
ArmchairBuilder.com
The transceiver uses a "classic" double-balanced or diode ring mixer.
I have used Schottky diodes here.
The transformers wound on the ferrite cores are trifilar wound and designed to drive the balanced diode network from the unbalanced source, and converslely to match the balanced diode network to the unbalanced load.
Switching between transmit and receive modes inverts the source and load - ie it is bi-directional.
I will be looking for an oscillator drive level of around +6 to +10 dBm for good performance.
The circuit board is approximately one inch (25mm) long.
Postscript :
After completing the "Phase Locked VFO" which covers 81-81.5MHz (approx) and which produced almost exactly +10dBm, I found I had to put a matching pad based on a "pi" network designed to produce 6dB of attenuation in a 50-ohm system, in series with the LO drive to this mixer.
I suspect the problem was due to the somewhat "iffy" impedance presented by the mixer to the slightly "touchy" amplifier in the PLVFO. The pad disguised the load from the source and all was then well.
The "deluxe" version, featuring homebrew TX/RX changeover board.
The case is plastic (neat but probably a mistake!) It was to hand and was about the right size.
The transmitter was designed by George Burt GM3OXX and was originally intended to fit on a one-inch-square PCB, hence the name.
One inch of PCB seems rather impractical to me, so I expanded the PCB to slot into this project box , and I then added the TX/RX changeover board to make the transmitter integrate with an outboard receiver.
I have had LOTS of fun operating this little radio!
Both sets of vanes (moving and fixed) are "hot" with RF, and as the case is plastic it suffers a little from "hand capacity" effects.
A metal case and a different arrangement to isolate the tuning control would have been better with hindsight, still one of the benefits of home-brewing is that you always learn quite a lot in the process ...
In this economy, some are doing better than others (and me!). A huge new home being built on the golf course, three houses down from where I am working.
Eden9 project moves on a bit more.
Unit has been powered and appears to work, so far so good.
(as it later turned out the two MOSFETs which switch the 8V rails appropriately to RX and TX sections were actually connected incorrectly. No harm was done and the mistake rectified, but the resulting correction isn't exactly pretty!)
The loop of wire on the right hand side of the board (in contract bridge parlance "east"!) forces the unit into "receive" mode. When the unit is finished the "fixed 12V" "receive 12V" and "transmit 12V" will be wired to the three solder "lands" you can see in this area of the board.
The cascode IF amplifier stage has appeared at the bottom left, but is not quite completed.
Next step: Finish of the IF amp, build the IF ladder filter and a full functional test of all stages completed so far.
The Eden9 board has acquired a few more parts, and is pictured from the other side with respect to the first photograph.
Mic preamp and modulator stages are now fairly complete and ready for a final scrutiny (looking for wiring errors and other faults) before the ICs are inserted into their sockets and power applied.
The component density is somewhat higher than I had envisaged, and I am finding the component placement and soldering somewhat "challenging" to say the least!
... a little before my time, but magazines from this era are quite fascinating to "technology archaeologists".
Technical advances made during the conflict years of 1939-45 are starting to find their way into the civilian world, along with ex-military and military surplus equipment.
You can pick up similar magazines cheaply on the likes of EBay (I have had this one stashed away in my loft for more years than I care to remember!), and make interesting reading.
Why not scan them and put electronic copies onto the web for everyone to enjoy?
I expect that one shilling (the cover price) was quite a lot of money in 1952!
Mixer and Preselector Filter stages have now been added (but not yet tested), the filter interstage coupling wires are missing.
The stages from the bilateral amplifier through to either loudspeaker or microphone input have been tested, and appear to work.
Please feel free to use this photo but be sure to credit ArmchairBuilder.com and provide this link...
armchairbuilder.com/resources/how-to-build-your-own-home
Thanks,
Michael
ArmchairBuilder.com
Shot this on a rainy day in Georgia. The home to be is just off of Northside Drive in the Buckhead neighborhood. Used my LG 2's 8 megapixel camera to snap a few shots. This image is considerably cropped, straightened and clarified in Phototoaster.
Feel free to use this photo but please credit ArmchairBuilder.com and provide this link...
armchairbuilder.com/resources/how-to-build-your-own-home
Thanks,
Michael
ArmchairBuilder.com
p.s. - let us know about it....we love seeing our photos in action!
Stock photo of the wood frames of the second floor of a new urban housing development under construction.
"Northmore" Construction, ca. 1937. Photographer Unknown, Rossetti Collection. Reference number: 82-834-7534. Beaton Institute, Cape Breton University.
The ABS enclosure (RS Components item) is ideally sized for this unit, if not exactly the ideal material from an "RF hardness" point of view.
There is still room for one or two modifications I have in mind (principally provision for a "passive bypass switch" arrangement.
Sexy blue internal mood lighting from a handheld miniature "White LED" torch (flashlight!)
Smartphone mounted on cheap eBay miniature table tripod - much better than being hand-held!
Mode Selection switched and AF output level pot fit nicely into the lid of this ABS project enclosure.
Spot the couple of soldering iron slips (Oops I've melted the plastic case again!)
Read the post about the master suite framing at akhouseproject.com
Note that the framing pictured here was demolished due to extensive and unfixable construction defects.
This photo is provided under a Creative Commons Attribution license. Please provide the following credit: "Photo courtesy Paxson Woelber, akhouseproject.com"
Please feel free to use this photo but be sure to credit ArmchairBuilder.com and provide this link...
armchairbuilder.com/resources/how-to-build-your-own-home
Thanks,
Michael
ArmchairBuilder.com
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