Ken Scharf ) writes:
xpyttl wrote:
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

..
There are two ways of looking at cascade, the devices are in series for
dc and ac, or only ac. The above link shows the latter. I had an idea
for a hybrid cascade amp of the first kind. The input would be a jfet
which sorta becomes the emitter resistor for a bipolar transistor as the
second stage of the cascade amp. The bipolar is run in grounded base
(for ac, normal bias network and base bypassed to ground with a cap).
Would give the advantages of high input impedance of the fet and high
gain from the bipolar.

It's been done. There was an article in Ham Radio magazine in 1970 or
1971 about a six meter converter. Just as you described, a common source
JFET with a bipolar transistor as the upper element. Used a Vackar oscillator
to make it tuneable. It might be this one:
Six-meter converter, improved K1BQT 50 Aug 70
The date is about when I remember it, though I don't remember K1BQT being
the author.

Michael VE2BVW

Michael Black wrote:
Ken Scharf ) writes:

xpyttl wrote:

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

..

There are two ways of looking at cascade, the devices are in series for
dc and ac, or only ac. The above link shows the latter. I had an idea
for a hybrid cascade amp of the first kind. The input would be a jfet
which sorta becomes the emitter resistor for a bipolar transistor as the
second stage of the cascade amp. The bipolar is run in grounded base
(for ac, normal bias network and base bypassed to ground with a cap).
Would give the advantages of high input impedance of the fet and high
gain from the bipolar.


It's been done. There was an article in Ham Radio magazine in 1970 or
1971 about a six meter converter. Just as you described, a common source
JFET with a bipolar transistor as the upper element. Used a Vackar oscillator
to make it tuneable. It might be this one:
Six-meter converter, improved K1BQT 50 Aug 70
The date is about when I remember it, though I don't remember K1BQT being
the author.

Michael VE2BVW

Nothing new under the sun!
Guess I need to get the HamRadio collection on CRrom.

Michael Black wrote:
Ken Scharf ) writes:

xpyttl wrote:

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

..

There are two ways of looking at cascade, the devices are in series for
dc and ac, or only ac. The above link shows the latter. I had an idea
for a hybrid cascade amp of the first kind. The input would be a jfet
which sorta becomes the emitter resistor for a bipolar transistor as the
second stage of the cascade amp. The bipolar is run in grounded base
(for ac, normal bias network and base bypassed to ground with a cap).
Would give the advantages of high input impedance of the fet and high
gain from the bipolar.


It's been done. There was an article in Ham Radio magazine in 1970 or
1971 about a six meter converter. Just as you described, a common source
JFET with a bipolar transistor as the upper element. Used a Vackar oscillator
to make it tuneable. It might be this one:
Six-meter converter, improved K1BQT 50 Aug 70
The date is about when I remember it, though I don't remember K1BQT being
the author.

Michael VE2BVW

Nothing new under the sun!
Guess I need to get the HamRadio collection on CRrom.

Sure, there are _op-amps_ that have cascode input stages. There are
bootstrapped cascode input stages used in feedback amplifiers that
have extremely low input capacitance and very low distortion when
driven from high source impedances. One of the FM tuner manufacturers
long ago used a cascode input stage. With transistor amps, you can
run the input transistor at low voltage and therefore low dissipation,
and have the output transistor capable of large swings, and thus get
good dynamic range. I don't know that there's any particular noise
advantage, per se. But it does let you pick the best transistor for
each part. Another variation with transistors is a "folded cascode"
where the input transistor is one polarity (e.g. NPN) and the output
one is the opposite polarity (PNP).

Cheers,
Tom

oUsama (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

Sure, there are _op-amps_ that have cascode input stages. There are
bootstrapped cascode input stages used in feedback amplifiers that
have extremely low input capacitance and very low distortion when
driven from high source impedances. One of the FM tuner manufacturers
long ago used a cascode input stage. With transistor amps, you can
run the input transistor at low voltage and therefore low dissipation,
and have the output transistor capable of large swings, and thus get
good dynamic range. I don't know that there's any particular noise
advantage, per se. But it does let you pick the best transistor for
each part. Another variation with transistors is a "folded cascode"
where the input transistor is one polarity (e.g. NPN) and the output
one is the opposite polarity (PNP).

Cheers,
Tom

oUsama (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

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

"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

You are working at it wht wrong way. The three things you mentioned do not
go together. What you want is somthting with strong signal handling and low
noise. You use just enough gain to override the mixer noise. Then make up
the gain at the IF stages after the filters.

"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

You are working at it wht wrong way. The three things you mentioned do not
go together. What you want is somthting with strong signal handling and low
noise. You use just enough gain to override the mixer noise. Then make up
the gain at the IF stages after the filters.

"Ralph Mowery" ) writes:
"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

You are working at it wht wrong way. The three things you mentioned do not
go together. What you want is somthting with strong signal handling and low
noise. You use just enough gain to override the mixer noise. Then make up
the gain at the IF stages after the filters.


Or, no rf stage at all.

I can't remember what frequency this if for, if it was mentioned.
An RF stage is only needed if there is need, like one needs front
end selectivity to eliminate images or to keep the mixer from overloading,
and the amplification is there to overcome the losses of the filter.
Another need would be that a good low noise stage is needed because
what comes later is too noisy.

Michael VE2BVW