zaterdag 7 september 2013

Multiband Bitx: The MK1 Exciter

After not posting for two months now,it`s time to post a new blog about my Multiband Bitx.A few months ago I purchased the Multiband Bitx kit by Sunil and a ordered the G6LBQ linear PCB by DXKits.In the meantime I spent some time to build the bitx20 V3 in dead bug style,waiting for my parts for the multiband.Now the exciter is finished and tested.The manual which you can download from the G6LBQ Yahoo group is quite good,so I`m not gonna bore you with pictures where the different stages of the build are displayed.I choose to build the MK1 version of the multiband in stead of the MK2 version which is now availible,because I had all the parts already in stock.


On the picture overhead you see the exciter with the little ad-on crystal filter.Just like my Bitx20,I paired 6 crystals with the use of my BFO and a frequency counter.(Picture bellow)You need four crystals for the filter and one for the BFO.I paired six,because I want to put the USB/LSB mod on in the future and that requiers another crystal.For the IF I used the 10MHz crystals.Remember always to put the crystal with the lowest frequency in the BFO section.For T1 in the BFO I used a coil from Sunils Bitx20 bandfilter with a 82pf padding capacitor.Special attention when you solder Q4 (2N3904) on the PCB.Earlier versions of the PCB had an error in the pad positions for the transistor.On my PCB,this error was corrected.


During the build,you have to test the individual completed stages.I constructed two toggle switches on a PCB so I could switch from TX to RX and 12V on/off.


After putting all the parts on the PCB it was time to test the circuit.I connected a speaker,antenna and a volume pot.Because I didn`t build the bandfilter yet,I bridged the bandfilter connection with a piece of wire.After switching on the power,I could hear two Dutch radio stations.Not bad.Time to connect the VFO.For the VFO I used the IK3OIL.The difference between a VFO or without a VFO was big.An increase of audio output and several stations and CW all togheter.Next week I will start with the bandpass filter.





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