?I had the day off today and have been playing around with the BITX40v3 on the work bench this morning . I wanted to see how easy it would be to modify it to other bands. After some?discussion on here , I decided 20 m was probably the easiest , so in true ham radio form , I put soldering iron in hand and hacked away . I started with the VFO . To test rx on 20 m I used a 2.010 Xtal I had laying around. By replacing the VFO coil with the 2.010 xtal and bypassing the receive BPF I am able to receive BOTH 14 Mhz signal and 10 mhz source signal (of course with no filtering ¡) from the RF generator . After some more discussion and suggestions on here , I went back at it after lunch .
Ashhar had suggested replacing the 40m 100pf caps to 22pf for 20m, and Ken VA3ABN reminded me of that this morning , so?I went and replaced the BPF caps as follows - C2 , C4 and C6 with 20 pf as that was all I had in the junk box . But I found had better receive results when I changed C6 to 18 pf . I left the others at 20 pf . I then changed out the Xtal I had installed earlier in the day and reworked the VFO . Changed C95 to 680 pf and increased the inductance of L4 to 13.5 uh ( from the junk box ) . This put me in the ballpark with a VFO freq range of about 2.2 MHZ .
The receive results were instant , copying 20 m SSB sigs on a dipole with open wire and a tuner . Do not know about the sensitivity yet , but it does receive on 14.2 MHZ ! ?The extra capacitance at C95 has decreased the band coverage of the varactor . Maybe with some more inductance at L4 and reducing C95 to 50 pf or so the coverage should be quite good with a 10k 10 turn pot. Will save that for another day.?
