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CONFESSION TIME: this project has gone to the bottom of the pile at the moment (Nov 2011)
as I am busy with too many other ideas and projects. It will get finished one day, bit not soon.

Update on Progress

• Breadboarded TX AF amp, single balanced diode mixer, buffer and IRF510 FET PA. Power out currently about 1W pep. Will try a different PA device (2N3866) with the aim of reaching at least 2W pep although I think the IRF510 should be able to reach this target.
• In the end I went for a FT37-43 toroid for the balanced mixer rather than a 28MHz tuned circuit. Currently the rest of the TX line-up is quite broadband and I may be able to trade some gain and Pout for bandwidth with some optimisation.
• TX low pass filter
  

Introduction

A work in progress - check back over the next 6 weeks to see this design take shape

Yes, you read it correctly: a simple sideband (not single sideband) rig for 10m (28MHz). By simple I mean of course a double sideband supressed carrier design. This has been a project idea for too long, so now is the time to create this. What I have in mind is a simple, small rig to use from home or out portable to work local SSB stations and the occasional DX when conditions are favourable. As with many of my projects, this is a "work in progress", so come back regularly to see how this develops. Already I have breakdboarded many of the subsystems needed, so putting these ideas together should not be difficult.

Specification

These are the outline requirements currently:

• TX power ~2W pep (equivalent to 1W pep SSB). 5W pep would be better though, but higher power increases interference risk to others from the unused sideband.
  
• 0.5uV sensitivity direct conversion receiver
• 300mW AF ouput
  
• Tuning range 28.4-28.6MHz (possibly VXO controlled over a smaller 25kHz range in a simpler version)
  
• Possibly a CW option covering 28.0-28.1MHz
• Small, single PCB design using commonly available parts. Initial version will be built "dead bug" style.
  
• Simple, compact housing e.g. diecast box or aluminium box from Maplins.
• Target cost for ALL parts £20 ($32).
  
• Easy to reproduce.
  
• I'd like this design to become a classic and one that helps others get onto this great band.
  

Design Ideas

Nothing too unusual here at all: standard design elements found elsewhere will be used (where already designed and available) from sources like the GQRP SPRAT magazine and the internet. I will try to make the design simple without overdesign. This is a common mistake, I feel, in many published designs, especially for a single band rig. For example, why use wideband matching between TX stages when with narrowband designs a higher gain can be achieved with fewer stages?

For the receiver, simple approaches such as the NE602 integrated IC mixer is adequate for the intended use: most stations that will be worked will be using at least 10W, often 100W, so that sensitivity does not have to be fantastic, just adequate. Also, the IM2/IM3 performance of the NE602, although not fantastic, is fine for such a simple radio, especially if the input filtering is reasonable.

The advantage of the DSB approach is the design simplicity with no need for expensive SSB filtering. The downside is the waste of power in the unwanted sideband and the risk of some LSB interference to adjacent channel stations. In a later version, a phasing design may be considered to attenuate the unwanted sideband by around 20-30dB. Another problem is tha receiving another DSB signal can be difficult, although not impossible.

TX line-up

TX Audio

VFO

Direct Conversion Receiver

Design Idea Sources

Here I will add any links from where ideas have been found and used. This should encourage others to look at these sources for their own versions.

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