Monday, June 22, 2009

Read the datasheet

Why am I writing this... because my aviation band receiver was not receiving what I wanted, only some aircraft's passing by, nice music on 88-108, some packet on 144.800 but I couldn't get VOLMET (meteo info) on 126.400 but my TM-D700 could receive on the same place and with an inferior antenna (it's bad when your own homebrew receiver is inferior to a commercial unit that took years to develop....)

I allways say: "RFTM" (read the friendly manual)......but never do it myself :)

After testing numerous TA7358 schematic configurations I found on the internet, finally decided to look carefully at the IC datasheet and go some conclusions:

"Wide supply voltage range: Vcc = 1.6-6v": some schematics have a Vcc of 8 or 9V ??? IC max supply at 25ºC is 8V .I tested to 12v....it survived ,Inow set it to 6V

Look at the schematic in the datasheet and you will see a tuned circuit at pin 3 (rf amp out): Some shcematics don't have a "by the book" tuned circuit...have something else...my circuit now has one and the internal rf amp is "tuned" and tunable. Removed the external rf preamp since there is no need of a rf preamp connected to pin 1 (rf preamp in), just a bandpass filter. If you put a preamp before it will overload the poor IC expecialy in hurban environment

After some testing and configuration change on the TA7358 I now can receiver VOLMET, with some noise in the background but readable, now it's time to improve even further...

I found out that if you trow a TA7358 to a PCB it will work, limited but will work, but if you whant to get all the juice from it you have to push hard and test a lot... will post some more news later.

If you copied my receiver schematic you will have a limited performance.. I told you so...never trust an internet schematic...

....and the squelch design is also broken... also working on a new one (my own design).

No photo today! Read!

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