Author Topic: 5W PLL  (Read 13546 times)

MDH

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5W PLL
« on: August 27, 2012, 04:00:16 pm »
Hi everyone. I've been following the pira site for a good few years so i thought i'd join the forum.

I'd like to know more about the 5w pll tx http://pira.cz/entx4.htm

I want to know more about TR1. Is this part of the matching between stages? is there an alternative? for example using a toroidal ferrite or even just a capacitor? also, what is R9 for on the base of Q3?

The oscillator looks like it operates 'on frequency', am i right?




DJ Adam Eve

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Re: 5W PLL
« Reply #1 on: October 03, 2012, 09:33:45 am »
Hi everyone. I've been following the pira site for a good few years so i thought i'd join the forum.

I'd like to know more about the 5w pll tx http://pira.cz/entx4.htm

I want to know more about TR1. Is this part of the matching between stages? is there an alternative? for example using a toroidal ferrite or even just a capacitor? also, what is R9 for on the base of Q3?

The oscillator looks like it operates 'on frequency', am i right?





TR1 is an impedance transformer, stepping down the impedance from the BFG135 to the base of the 2n3553/2sc1971, hence they have different windings for each. From memory i think the ratio is 3:1 or 2:1, that's the turns ratio, which is the square root of the impedance ratio (so impedance ratio is either 4:1 or 9:1), so for the 2:1 ratio you could use a bifilar 4:1 torroidal transformer (Google) but why bother? There's alternative ways to build it with ferrite beads.

The oscillator is 'at frequency' and puts out a fair bit of power.
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RIGMO

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Re: 5W PLL
« Reply #2 on: April 14, 2023, 05:03:04 pm »
Quote
the Jan Kolar "Pira" effort works reasonably well, though its performance is almost entirely determined by the construction of the inter-stage coupling transformer and the careful alignment of the output stage trimmer capacitor.  It also has the (minor) inconvenience of using an obsolete PLL IC (which will be difficult to find in future) and the firmware forces a "re-tune" every half-hour, which can put small noise bursts on the carrier. 

 Is this caused by not connecting pin 4 (MCLR, RA5, Vpp) to 5V through the 10k resistor?


Jan

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Re: 5W PLL
« Reply #3 on: April 17, 2023, 09:00:29 pm »
The periodic retune is really present in the firmware. It prevents permanent PLL lock-out, for example due to transient effects on power line.