[UNTRIED IDEA] Bitx40 conversion for 6 & 2 metres #bitx40 #6meters

Peter Parker

Many would have the old Bitx40 (especially the free running VFO version) and have little use for it now they have a uBitx. 

A possible idea could be to convert it to 6 metres and potentially 2 metres as well. That would make it a great field day portable rig. 

Even a few hundred milliwatts to a small yagi should cover several hundred km under a good path. 

*** These are ideas only - I have only done a small amount of work towards this. ***

1. The first thing is that you will need to add a DDS-based VFO. I used the CDV from OzQRP.  

Video at https://www.youtube.com/watch?v=K5Vtih9Nxhc

More about the CDV including manual at http://www.ozqrp.com/CDVindex.html 

Most notable is that it goes up to 100 MHz (which could be significant - see later).  

2. Next you will need USB rather than LSB. This can be done without fiddling with the carrier oscillator by flipping the local oscillator to the other side of the 12 MHz crystal filter. 

Eg instead of the LO for 7 MHz being 5 MHz it needs to be 19 MHz.  That will give USB on 7 MHz.  I needed to make menu setting adjustments in the CDV to do this.  This includes getting the dial frequency right. 

3. With a USB receiver set up (Eg FT817) move up to other bands - eg 10, 14, MHz and up and transmit. You will hear yourself though it will be weak since the band pass filters and pi network won't be right. 

And the receiver will be insensitive.  Keep moving up to 50 MHz. 

4. For testing purposes you can remove the 7 MHz band pass filter. This will dramatically improve receiver sensitivity. But you might get breakthrough from other signals. On transmit you will get a bit more output
(your RF power meter needle will wriggle slightly) but it will still be low due to the 7 MHz pi network in the output and the likely low gain of the IRF510 on 50 MHz. But at least it should sound good on the FT817 giving  you something to go on. 

5. (haven't got this far yet) Add a 50 MHz band pass filter where the 7 MHz filter was.  That should make the receiver OK though I wouldn't be surprised if it's deaf - you will likely need to add a FET RF preamp. 

6. As for the transmitter you will probably need to remove the IRF510 and try another configuration (possibly 2 transistors).  You might only get 500mW to 1w output. But that might still be OK with a good antenna. 

7. What about 2m? You will need a transverter. The CDV VFO has a second fixed output that can go up to 100 MHz.  50 MHz + 94 MHz = 144 MHz.  So it might be possible to use this in combination with transmit and receive mixers to get 2m.  This could be built in the same box as the Bitx to make a portable QRP VHF package for field days etc. RF transistor are hard to get but even 500mW to 1w on 2m can do well eg video below. 



73, Peter VK3YE






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