Wednesday, July 28, 2010

Summer and 1W at VHF

Summer is until at least end of August there will be few chances to spend some quality time in the shack (eg: doing soldering). Today at 22H00 there were still 36ºC inside the shack and it's isolated, I wonder if it wasn't.
Anyhow managed to make some more tests on the amplifier for the VHF FM transmitter I am building from my own schematic, since the ones I found were using un-existing components locally or were using dubious components for the function...namely frequency limit. For now I am getting already an impressive 100mW (more or less the test probe accuracy) from a 1.6mW input .... funny is that in the first tests I made (sightly different design) I managed at least 1W output first time (didn't measured exactly but the 1W dummy load was getting pretty warm), unfortunately it was not stable. The 100mW I am getting are "made" at the expense of 2.4W DC power so there's a long way to improve.
I Started from a design including 2n2219A, 2n3866 and a 2n3553 transistors but since the 2n3553 is 3 Eur cheaper than the 3866 (go and figure this one out...) I am now in the second stage of the 3 stage 2n3553 amplifier. Hope to get 1W when the third stage is complete. As always the schematic will be placed here when is fully tested and stable enough... not like many designs found in the internet.
One thing is for sure, you can easily get 1W at HF but to get 1W at VHF is a different story. After the 1W is accomplished the final 5W I want will be using an amplifier module, cheaper than the transistors needed for getting the 5W power mark.
Will continue this story, hopefully in short time...

Meanwhile have a nice summer.. or winter if your live in the southern hemisfere...

This time a photo from last weekend, and hopefully the next one, beach:

p.s. not mine the photo but will take and post some in the future.

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