On 4.7.2011 7:31, clifford wright wrote:
Good day!
Can anyone point me towards a good design for a good RF stage for my home
brew HF receiver. I have no less than 6 others hams in my small town and
one within 400 metres, so I need good strong signal performance.
10 to 15 dB gain would be ample, but I would like to have 50 Ohm input and
output impeadances.
The receiver is an upconverter to 45MHz with a 15 kHz bandwidth xtal filter
followed by a downconverting mixer to either 9MHz or 10.7 MHz with separate
IF strips.
Tuning is by a PA0KLT synthesiser.
I have been a bit out of touch lately and am not very up to date with the
latest MOSFETS etc. The mixers use the 1992 Ulrich Rohde FET double
balanced mixer circuit.
The rest of the sytem was built back in the early 1990's but put to one
side until a better frequency sythesiser was available.
Now it looks like the time to get things moving again!
Regards Cliff Wright ZL1BDA ex G3NIA.

Hello

Some late thoughts about amplifier candidate...
One simple but low cost one could be push-pull Jfet amplifier using
two J309 in parallel, gate grounded. Input can matched to 50 ohm using
1:0.7 input transformer ( fets do have lower input impedance than 50 ohm
) and output at drains can be 4:1 balanced transformer.
Spice analysis shows around 9dB gain and very good wide-band input
matching, probably noise figure is also not much greater than one fet
alone, actually it should be lower. One thing needed is quite equal
fets, Idss and Vp, four matched fets should be still easy to find.
Sorry don't have more exact figures to give, but this could be one
candidate to evaluate.

br Kari B
Oh6io