"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

Ralph wrote:

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.


Not really. What you say is the general "wisdom".
I want low noise, high (adjustable) gain preselector. Something with below 0.1
uV. There are situations when that is needed (small loops receiving antennas,
Beverages on low bands, etc.) The gain should be adjusable so it is (band
noise) just above the noise threshold of the mixer for particular antenna/band
situation.

At the same time have high dynamic range to handle strong signals S9+60dB
without overload.

Way back I modified Drake R4B by putting 6EH7 as preselector with separate RF
gain control. It worked very well and it is still hard to beat.

Yuri, www.K3BU.us

Ralph wrote:

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.


Not really. What you say is the general "wisdom".
I want low noise, high (adjustable) gain preselector. Something with below 0.1
uV. There are situations when that is needed (small loops receiving antennas,
Beverages on low bands, etc.) The gain should be adjusable so it is (band
noise) just above the noise threshold of the mixer for particular antenna/band
situation.

At the same time have high dynamic range to handle strong signals S9+60dB
without overload.

Way back I modified Drake R4B by putting 6EH7 as preselector with separate RF
gain control. It worked very well and it is still hard to beat.

Yuri, www.K3BU.us

On 04 Apr 2004 01:16:22 GMT, oUsama (Yuri Blanarovich)
wrote:


Not really. What you say is the general "wisdom".
I want low noise, high (adjustable) gain preselector. Something with below 0.1
uV. There are situations when that is needed (small loops receiving antennas,
Beverages on low bands, etc.) The gain should be adjusable so it is (band
noise) just above the noise threshold of the mixer for particular antenna/band
situation.

While you definitely need the lowest noise figure and a high gain when
using small magnetic loops, I very much doubt that you are going to
need the strong signal handling capabilities for these antennas. Why
not use a dedicated preamplifier constantly attached to these
antennas, possibly with some protection circuitry to avoid damage when
transmitting through your nearby transmitter antenna ?

With modern transistors you can get quite noise figures, however, some
transistors may obtain those low noise figures only at UHF and above,
since the 1/f may start already in the MF or HF range.

One other thing to watch when using devices with gain up to the
microwave bands is the direct pick-up of local FM and TV signals,
unless the circuitry is well shielded and the input filters contains
capacitors with low parasitic inductance.

Just switch the receiver input between the magnetic loop preamplifier
output and the full sized antenna and avoid the hassle with variable
gain stages.

At the same time have high dynamic range to handle strong signals S9+60dB
without overload.

You are going to encounter such signals from a full sized antenna, but
even at 14 MHz, the band noise is still quite high, so the ultimate
noise figure is not so important.

By the way, did you check the "A High-Dynamic-Range MF/HF Receiver
front end " by Jacob Makhinson N6NWP (QST February 1993 p. 23-28, with
corrections in June 1993 p. 73) ?

It contains push-pull preamplifier designs with feedback with nearly
+33 dBm input IP3 and gain compression starting around S9+80 dB.

Paul OH3LWR

On 04 Apr 2004 01:16:22 GMT, oUsama (Yuri Blanarovich)
wrote:


Not really. What you say is the general "wisdom".
I want low noise, high (adjustable) gain preselector. Something with below 0.1
uV. There are situations when that is needed (small loops receiving antennas,
Beverages on low bands, etc.) The gain should be adjusable so it is (band
noise) just above the noise threshold of the mixer for particular antenna/band
situation.

While you definitely need the lowest noise figure and a high gain when
using small magnetic loops, I very much doubt that you are going to
need the strong signal handling capabilities for these antennas. Why
not use a dedicated preamplifier constantly attached to these
antennas, possibly with some protection circuitry to avoid damage when
transmitting through your nearby transmitter antenna ?

With modern transistors you can get quite noise figures, however, some
transistors may obtain those low noise figures only at UHF and above,
since the 1/f may start already in the MF or HF range.

One other thing to watch when using devices with gain up to the
microwave bands is the direct pick-up of local FM and TV signals,
unless the circuitry is well shielded and the input filters contains
capacitors with low parasitic inductance.

Just switch the receiver input between the magnetic loop preamplifier
output and the full sized antenna and avoid the hassle with variable
gain stages.

At the same time have high dynamic range to handle strong signals S9+60dB
without overload.

You are going to encounter such signals from a full sized antenna, but
even at 14 MHz, the band noise is still quite high, so the ultimate
noise figure is not so important.

By the way, did you check the "A High-Dynamic-Range MF/HF Receiver
front end " by Jacob Makhinson N6NWP (QST February 1993 p. 23-28, with
corrections in June 1993 p. 73) ?

It contains push-pull preamplifier designs with feedback with nearly
+33 dBm input IP3 and gain compression starting around S9+80 dB.

Paul OH3LWR

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

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

By the way, did you check the "A High-Dynamic-Range MF/HF Receiver
front end " by Jacob Makhinson N6NWP (QST February 1993 p. 23-28, with
corrections in June 1993 p. 73) ?

It contains push-pull preamplifier designs with feedback with nearly
+33 dBm input IP3 and gain compression starting around S9+80 dB.

Paul OH3LWR


The mixer section is what is REALLY impressive about that front end.
There was another article (also in the handbook) about a similar mixer
that used a siliconix quad dmos fet that was even better.

By the way, did you check the "A High-Dynamic-Range MF/HF Receiver
front end " by Jacob Makhinson N6NWP (QST February 1993 p. 23-28, with
corrections in June 1993 p. 73) ?

It contains push-pull preamplifier designs with feedback with nearly
+33 dBm input IP3 and gain compression starting around S9+80 dB.

Paul OH3LWR


The mixer section is what is REALLY impressive about that front end.
There was another article (also in the handbook) about a similar mixer
that used a siliconix quad dmos fet that was even better.

Paul OH3LWR:

While you definitely need the lowest noise figure and a high gain when
using small magnetic loops, I very much doubt that you are going to
need the strong signal handling capabilities for these antennas. Why
not use a dedicated preamplifier constantly attached to these
antennas, possibly with some protection circuitry to avoid damage when
transmitting through your nearby transmitter antenna ?


The idea is to have one preamp or RF stage for whole range of antennas 160 -10
or 6 m. No outboard boxes, preamps, but one good "in house" adjustable gain
amp. No step or switchable attenuators either. Normal city mortals have high
band noise levels, but when you go to the ocean front, use RX antennas or beam
north on high bands, you need sensitivity and of course high dynamic range for
the other end of the signals spectrum, like operating in Multi/multi
environment.

Thanks for N6NWP article info, I will look it up.

Yuri, K3BU.us