Thursday, November 21, 2013

14.318 Mhz. CW, 20 meter transmitter

14318kc transmitter:-

bitx version-1 (by vu2ese) linear
This is a 20 meter transmitter brewing up after long 10 years of absence in homebrew. So, the technique is of old faithful transistors ( he he ! in the age of digital the transistors are also old tech !)

Here cheaply available (rs.15) fundamental Xtal is used. 14.318 Mhz which falls on the one end of the ham band. But, generally hams does not go that much high up ! so, with this tx sked is needed. And one possible benefit will be there will be less QRM of QRO rigs. around 14.200kc band is crowded.

1. First board:- Xtal osc with buffer. This ckt is standard. Here 1k pot is used to control the RF going into the RF amp chain.

2. Second Board:- This is the single stage tuned amp. I have used the BF494 but any c series transistor can be used. If it does not work nice will change it to 2n2222 in metal pack. Here, old alladin former is used as tank of tuned amp. This is 10 years old legacy.

3. This board consist of driver amp based on 2n2218 and RF power amp based on IRF510. This is very straight and standard amplifier. Heat sink is must for IRF.  Output filter is not designed at present. Once it heats up dummy load filter will be made and connected to the dipole. I am expecting power of about 5w.


Only part tested is upto driver amp. I am thinking of making the RF power stage on the basis of VU2ESE, OM farhans bitx20 v1 (first version using the tap-washer !)  i.e air core transformer. But, vu2*** informs about different version of this output transformer . So, will try his suggestions also. And see which thing works for me. Only thing important is working ckt. I am ready to borrow from any idea, but it must work me.

NB:-At present (nov2013) this project is not complete. I want to power finale amp from 18vdc to increase power,so it will need few more changes.  ( I did power up with 24volt  got around 3-4watt, disliked using  two different voltages for single transmitter thus ended up using 12volt and 2watt ok.)

As of 28 Jan 2015 I did not drive the exciter with 18/24 on the final irf510 instead accepted whatever power it produced with 12vdc and drive it to external linear. This big linear produces around 20watt and punching whole indian continents.

Will upload the finished fotos. soon....

As of 14 feb 2015 made replica of this transmitter. It works. People are making the transmitters for this freq. It will become popular one day. de vu3inj, indrajitsinh.