vrijdag 20 september 2013

Multiband Bitx:The MK1 Bandpass Filter

This week I finished the build of the Multiband Bitx Bandpass filter.In the beginning of March 2013,I purchased the complete G4CFY bandfilter kitt by Spectrum Communications.In the meantime there was a re-development of the choice in components ,used in this bandfilter.So I needed to do another investment to buy those components used in the revised 29May kit.Spectrum Communications can supply you a kit with the changed capacitors and the 3 coils for the 30M band.I also purchased the switching parts.(BA243,33uH chockes and 100ohm resistors).So now I have the latest version of the bandpass filter.Just follow the manual in the building process.It`s no rocket science.Be carefull do when you install the ceramic capacitors.Several NPO capacitors have a 2,5mm pitch while the PCB has a pitch of 5mm.Don`t stick the capacitors to the bottom of the PCB.The risk of destroying your priceless NPO capacitors is very high.Just leave them a couple of mm`s above the PCB.After the build was done,I connected the bandfilter to the Multiband Exciter.I didn`t hear anything,only a little noise out of the speaker.Silly me,I forgot to give the bandfilter a supply power.Now I heard several stations immediately,but they seemed to be some KHz of frequency.That problem was soon discovered.As you can see on the picture on the MK1 Exciter blog,you see that I measure the BFO frequency.The reading say`s 9,999,26MHz.That`s way to high.I had to adjust the BFO frequency by means of the trim capacitor to 9,997,50MHz or so.With the 4,7uH chocke I used,I couldn`t come nowhere near this frequency.The range was to small.So i changed the chocke coil for a 10uH from an earlier Bitx 20 V3 build.Now I could adjust the frequency to 9,997,50 MHz.With the IK3OIL VFO connected to the Exciter,it was time to listen for any activity on the band.The first QSO I heard was a Italian station having a QSO with a station located in Florida USA.Not bad for a homebrew rig which hasn`t been alligned yet.Now what`s next.I will order a VFO.I think I go for the PA0KLT VFO.First I`m gonna build the PCB`s in a case.I still have a simular case in which my Bitx20 V3 is situated and that looks nice,so why not use it then for the Multiband Bitx.


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.