Friday, March 30, 2012

2m FM TX

Here's a duplication of LY3H design with my usual variation...eg...replacement of some components by lack of them in the local electronics shop.

The original schematic:



Here's the outcome:


I didn't had BFR93 transistors so replaced by BFR91 and the BFG591 was replaced by an 2N3535. RC4558 is basically a double LM741, so I used the LM741. The tunable coil was replaced by a red core toroid with around 30 turns and frequency is set by mean of a 25pf trim capacitor.
The critical part are the first tuned circuits at 72.5Mhz, nothing a good dip meter doesn't handle, I had to remove one turn on L2 and L4 to put on frequency. Also with the direct replacement for the 2N3553 I am only getting around 0.6W, probably with some tuning 1 W could easily possible.

Since the frequency control crystal has a glass envelope why not put a LED behind to make it glow....looks like a magic eye tube. I used a double color LED, so green color when in rx and green mixed with red on tx...



The box came from an old CD-ROM drive.

I am now in the process of adding a tone encoder (top right board on the box) and a different mic (dynamic) so those results will be posted as soon as I finish it.

I'm very happy with the design and probably will be the shack main rig for repeater access.

Thank you LY3H for the design an help.

Have fun!

Thursday, March 22, 2012

Next project

No it's not a copy of HAL9000....(but i've had a Linux machine named that way!)

During build process...More details when's fully operational....

Now... what shall I do with 4 modules like the one bellow...
They reached the end of life in a nearby garden but still operational....

Monday, March 12, 2012

FM for the Bitx ? II

More ideas on easy and cheap FM add on (RX) for the BITX transceiver...

With an TA7303 and a 10Mhz crystal between pin 6 and 7 ?...
The original idea uses an ceramic element...

The cheapest TA7303 I could find costs 1.03 Eur...

And a circuit similar to one I've tested on another post:


The above one is a little bit more tunable and probably uses more easy to find components...without a limiter in front you probably "get" AM as a bonus!

I have to test...

Have a nice week... this was my weekend:

Wednesday, March 07, 2012

Low budget radio

Here for the low budget lovers....

Just having fun with the VFO on a "pound-shop" radio....

The new 500Khz band:


NOAA sat maybe?

It can go to 144Mhz... an a small transmission in the airband was heard...