Saturday, October 23, 2010

VHF trx on the shelf

Here it is....
On top of it, the 88-108Mhz FM receiver and the APT weather satelite receiver. On the right the Si570 VFO and the a TS-50.

Now, there's a little issue with the transmitter... I already knew it but kind of forgot... repeaters have a country wide 12.5Khz spacing but the PLL has 10Khz so I am going to miss some access to repeaters, for now I offseted a litle bit the reference cristal do get the 145.012,5Mhz needed for local access. Since this is not an elegant solution I am now looking for another PLL design probably leaving this one for a separate receiver (it's just a matter of programing the PIC).

Regarding the PA...I allready measured 2W on a 50 Ohm load (specs for the 2n3553 say 2.5W at 175Mhz and 28V, I have 13V and 145Mhz), with my uncalibrated test probe...anyhow it hit's the repeater nicely. I sorted the lack of TO-39 heat dissipator for the PA transistors making my hown model, here's the look of it:

Just roll a peace of thin piece of metal sheet around a 8mm drill and tighten a little to fit the transistor (around 7-8m according to 2n3553 specs).
I first tryed with aluminum kitchen foil but it get's to flimsy:

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