I'm still beavering away on my new TX and now have stopped blowing
up the
PA devices (fingers crossed).
I've incorporated some of the suggestions gratefully received:-
- Higher voltage FETs - IRF630's
- gate resistors to prevent vhf oscillation
I have also changed from transformer drive to using a 4426 driver
IC.
I'm generating 100 watts into my 50 ohm dummy load but
only getting an efficiency of about 50%.
The output transformer toroidal core is getting quite hot and I
suspect that it's permeability is too low as the capacitance
required
to bring it to resonance is far higher than those of published
designs
in the LF Experimenter's handbook, using the same number of turns.
These capacitors are running very hot too (as mentioned by PA0SE in
his LFEH article).
Has anyone a spare 3C85 toroid suitable for a PA stage which they
would sell to me ?
Alternatively I've looked in the RS catalogue but am not sure what
is a suitable type.
They quote a parameter 'AL' ( example 3225 nH)
From my old college days I remember uo and ur but what is 'AL' ?
73 Chris G3XIZ
This email is for the intended addressee only.
If you have received it in error then you must not use, retain, disseminate or
otherwise deal with it.
Please notify the sender by return email.
The views of the author may not necessarily constitute the views of EADS
Astrium Limited.
Nothing in this email shall bind EADS Astrium Limited in any contract or
obligation.
EADS Astrium Limited, Registered in England and Wales No. 2449259
Registered Office: Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2AS, England
| 