The tuner I mentioned did the cascode specifically to achieve low
noise and the ability to handle big signals with low distortion.
Somewhere in my disorganized archives I think I have more info on it,
but don't ask me to look! ;-) As I recall, they used a transistor
billed for CATV service with low noise and good linearity on the
input, and an RF power mosfet on the output--one of the old Siliconix
VMOS ones?? Haven't looked at it in 30 years, so I hope you'll excuse
my lapses of memory. In general to get low distortion, expect to have
to use fairly high current levels.

Do you have specific requirements? You may well be able to do fine
with a different, simpler design. I'd submit your requirement is not
for a cascode, but for specific TOI and perhaps harmonic performance
and noise level and input and output impedances.

Cheers,
Tom

oUsama (Yuri Blanarovich) wrote in message ...
Thanks for pointers, I will have look at references mentioned.
Another requirement would be good handling strong signals, like using 807 :-)

I am trying to build the converter with strong signal handling capabilities,
low noise and high gain.

Next step is looking at the mixers and low noise synthesizers.

Thanks a bunch!

Yuri, K3BU

Do you have specific requirements? You may well be able to do fine
with a different, simpler design. I'd submit your requirement is not
for a cascode, but for specific TOI and perhaps harmonic performance
and noise level and input and output impedances.

Cheers,
Tom


Low noise, high dynamic range, strong signal handling.
Again, useable for low signal RX antennas and handling strong in-band signals
like in multi/multi situations, when you want to tune/scan the same band while
transmitting on that band.
Filtering and protection is another story.

Low noise mixer is to follow, with low phase noise synthesizer.

Trying to beat K2 and Orion front ends.

Yuri, K3BU

On 4 Apr 2004 12:07:18 -0700, (Tom Bruhns) wrote:



Do you have specific requirements? You may well be able to do fine
with a different, simpler design. I'd submit your requirement is not
for a cascode, but for specific TOI and perhaps harmonic performance
and noise level and input and output impedances.

Cheers,
Tom


I really suspect that it is outlined an amplifier which it is not
expereinced whether it is needed or not, I believe it is no need for
extra amplification below 15 or 20MHz, and since the frame antenna is
relatively narrow banded it is no need for particularly good IP3
characteristics on any frequencies

Somebody once mentioned that a transistor with 50mA collector current
equalled a valve amplifier with 5mA anode current in respect of IP3,
wonder such is likely to be true? Suggested valve is 6761 with
gm=50mmho

73
Jan-Martin
LA8AK
http://home.online.no/~la8ak/e.htm
----
Jan-Martin, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/

Do you have specific requirements? You may well be able to do fine
with a different, simpler design. I'd submit your requirement is not
for a cascode, but for specific TOI and perhaps harmonic performance
and noise level and input and output impedances.

Cheers,
Tom


Low noise, high dynamic range, strong signal handling.
Again, useable for low signal RX antennas and handling strong in-band signals
like in multi/multi situations, when you want to tune/scan the same band while
transmitting on that band.
Filtering and protection is another story.

Low noise mixer is to follow, with low phase noise synthesizer.

Trying to beat K2 and Orion front ends.

Yuri, K3BU

On 4 Apr 2004 12:07:18 -0700, (Tom Bruhns) wrote:



Do you have specific requirements? You may well be able to do fine
with a different, simpler design. I'd submit your requirement is not
for a cascode, but for specific TOI and perhaps harmonic performance
and noise level and input and output impedances.

Cheers,
Tom


I really suspect that it is outlined an amplifier which it is not
expereinced whether it is needed or not, I believe it is no need for
extra amplification below 15 or 20MHz, and since the frame antenna is
relatively narrow banded it is no need for particularly good IP3
characteristics on any frequencies

Somebody once mentioned that a transistor with 50mA collector current
equalled a valve amplifier with 5mA anode current in respect of IP3,
wonder such is likely to be true? Suggested valve is 6761 with
gm=50mmho

73
Jan-Martin
LA8AK
http://home.online.no/~la8ak/e.htm
----
Jan-Martin, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/

The tuner I mentioned did the cascode specifically to achieve low
noise and the ability to handle big signals with low distortion.
Somewhere in my disorganized archives I think I have more info on it,
but don't ask me to look! ;-) As I recall, they used a transistor
billed for CATV service with low noise and good linearity on the
input, and an RF power mosfet on the output--one of the old Siliconix
VMOS ones?? Haven't looked at it in 30 years, so I hope you'll excuse
my lapses of memory. In general to get low distortion, expect to have
to use fairly high current levels.

Do you have specific requirements? You may well be able to do fine
with a different, simpler design. I'd submit your requirement is not
for a cascode, but for specific TOI and perhaps harmonic performance
and noise level and input and output impedances.

Cheers,
Tom

oUsama (Yuri Blanarovich) wrote in message ...
Thanks for pointers, I will have look at references mentioned.
Another requirement would be good handling strong signals, like using 807 :-)

I am trying to build the converter with strong signal handling capabilities,
low noise and high gain.

Next step is looking at the mixers and low noise synthesizers.

Thanks a bunch!

Yuri, K3BU

Thanks for pointers, I will have look at references mentioned.
Another requirement would be good handling strong signals, like using 807 :-)

I am trying to build the converter with strong signal handling capabilities,
low noise and high gain.

Next step is looking at the mixers and low noise synthesizers.

Thanks a bunch!

Yuri, K3BU

Jim Kortge, K8IQY, uses a cascode amp in his famous 2N2/40. He actually
uses it in the transmitter ... even with a passive mixer you don't need a
lot of gain on 40!

See http://www.qsl.net/k8iqy

...

"Yuri Blanarovich" wrote in message
...
Back from good old tube days, cascoded triode RF preamps were good for
high
gain, stability and low noise.

Anything out there in transistorised version, or there is there better
stuff
available? Looking mainly for preamps on HF to be used with low gain
antennas,
like small loops or beverages.

Yuri, K3BU.us

"Yuri Blanarovich" wrote in message
...
Back from good old tube days, cascoded triode RF preamps were good for
high
gain, stability and low noise.

Anything out there in transistorised version, or there is there better
stuff
available? Looking mainly for preamps on HF to be used with low gain
antennas,
like small loops or beverages.

Yuri, K3BU.us

Back in the 'good old tube days' it was difficult to get below a NF of 3 db
on 2 meters. Now it is easy to get way below that with a good FET. For HF
almost any RF device now will take you very low in NF with good gain.

There are versions of the cascode that use FETs for HF and above.

Yuri Blanarovich ) writes:
Back from good old tube days, cascoded triode RF preamps were good for high
gain, stability and low noise.

Anything out there in transistorised version, or there is there better stuff
available? Looking mainly for preamps on HF to be used with low gain antennas,
like small loops or beverages.

Yuri, K3BU.us

You definitely saw them in the early days. The one that comes immediately to
mind was a cheap preamp described in Ham Radio in the early seventies,
and was available as a cheap kit from Hamtronics.

I think there were some shown with bipolars, but I can't dredge up
any specific memories at the moment.

It was obviously a transitional thing, since you're right, one doesn't
see solid state cascodes very often. I have no idea if they were
used decades ago because it worked around limitations of early solid
state devices, or if it just seemed to be the thing to do since they
had been common in tube circuits.

The author of that Ham Radio article (actually, there were two, and he
used cascode FET amplifiers in various projects described later), I think
his name was Jerry Voigt, had grumlbed about the then relatively new
dual-gate MOSFETs, but in a followup letter he admitted than a dual-gate
MOSFET was basically a cascode device.

If there was an advantage to be using cascode circuits today, then
you'd be seeing them.

A lot has changed. Bipolars came in, and they couldn't handle strong
signals well. The JFET came along, and it was seen as the device
to use for best performance. The MOSFET came along, and again there
was a switch. Sort of simultaneously with MOSFETs, but not really adopted
till later, bipolars started being capable of low noise and strong signal
handling. MOSFETs are now rare for receiving applications. Gasfets came
along and they seem to be be the thing for low noise RF amplification.

Michael VE2BVW