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 Cliff,

try to find "Experimental Methods in RF Design" published by ARRL,
authors : W7ZOI, KK7B, W7PUA.

It is a gold mine of infos and circuits !

For excellent intermod quality, consider also H-mode converters.

This link is very informative :

http://martein.home.xs4all.nl/pa3ake/hmode/

73, Piero i5spo.


"clifford wright" ha scritto nel messaggio
...
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.

On Jul 3, 9:31*pm, 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.

Ah, one of my favorite subjects...

You don't mention any specific numbers you're trying to reach...

I've been working on something where I need a modest-gain HF amplifier
with good intermod performance. I have a couple of Spectrum Microwave
amplifiers that have about 20dB gain, nice noise figure around 3dB,
and about +55dBm TOI. But...they cost close to $1000 each, and need
400mA at 24V--about ten watts! That's fine for testing, but not to
actually use in the circuit, both the cost and the power dissipation.

For about a watt dissipation, I can get similar gain and almost as
good TOI--but poorer NF--using a couple op amp packages, the first op
amp to get the gain and the second to buffer the output and drive 50
ohms. The NF in the mid-teens is still good enough for HF work,
especially when faced with huge signals. If you look at differential
op amps designed to drive high speed ADCs, you'll find some pretty
nice third order distortion numbers. Parts from Analog Devices,
Linear Technology and Texas Instruments all come to mind.

As Piero suggests, you need to pay attention to the mixers to get
similarly excellent performance there -- and even to the crystal
filters, to be sure that they are up to the task of keeping distortion
low.

Also, I've built quite a few preselection filters for HF, and after
trying lots of different types of inductors (ferrite and powdered iron
toroid core, and magnetic-cored solenoid coils), decided that the only
coils I could use and guarantee adequately low distortion were ones
with non-magnetic cores...nominally "air" core coils. Unfortunately,
they are not as nice about rejecting external fields as the toroids,
so I've had to be careful about shielding.

I also spent quite a bit of time looking for switches with adequately
low distortion. I needed to switch filters quickly and potentially
millions of times, so I looked at every electronic switch I could
find. None of them was particularly good at HF. I found some tiny
reed relays, and they are OK, but even they contribute significant
distortion--barely good enough for what I was doing. Thankfully, they
last pretty much forever when switching RF at less than perhaps
+10dBm. RF armature relays that I've tested are all pretty darned
good--but have finite life.

Summary: if you want to be serious about low distortion, you need to
look at pretty much every part of the circuit. That includes asking
questions like, "Do I really need that RF amplifier, or is the NF
going straight into the mixer good enough?" and, "Can I rearrange the
circuit blocks to get even better performance?"

Cheers,
Tom

On Jul 4, 6:31*am, 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
Hi Cliff,

Piero and Tom gave you good comments.

If you need a strong front end your problem is not in the rf
amplifier. You need a strong 1st and 2nd mixer and for this there is
no better solution than the H-Mode Mixer. Having a una upconversion
1st IF, your critical point will be the 2nd mixer that will receive
strong signal amplified by this stage..

If you look at PA3AKE web page you con find info regarding my
simplified version I7SWX 2T H-Mode Mixer (http://
martein.home.xs4all.nl/pa3ake/hmode/2t-hmode.html). This has only 2
transformers and homebrewed, not purchased. You will see the info on
transformers winding, the one with 5 windings may seem difficult but
is not. In low bands you may avoid to have a preamp. Look at the G3XJP
project Pic-A-Star (RSGB RadCom and also reported in the Handbook).

73

Gian
I7SWX

www.hurricaneproject.altervista.org

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.

Why do yo need more amplification in front of your receiver. It's
making more sense to use a tunable preselector.And putting the
amplification in the IF's.

Regards,
Jan PE1SBG

When the band is open with lots of strong signals you don't want a
preamp, in fact you might want to switch in an attenuator to reduce the
signal strength into the first mixer. The K3 gives the user the option
of using a preamp or an attenuator (or BOTH(!) since the preamp has more
gain than the attenuator has attenuation so using both just gives less
gain). You also have the option of an IF preamp and two gain settings
for it.

In the Picstar there is a preamp using 4 parallel jfets that can be
switched as an RF preamp or an IF preamp. Since the Picastar's first
mixer is used on transmit and receive the preamp is used as an IF preamp
(actually postamp) on transmit. The use of the preamp in the receiver
for RF gives the best NF, while in the IF stage it gives the best IP.
The K3 uses a bipolar transistor for the preamp stage and there can be
some debate as to which type of preamp is actually better (probably the
bipolar gives the best IP and the parallel fet gives the best NF). I
think the fet preamp is preferred on the east side of the 'pond' and the
bipolar is favored on the west side.

Other than saving some parts (but costing something for switches) using
the same mixer bilaterally is probably not the greatest idea.
Personally, I would use the H-Mode mixer for the receiver and provide
the option to switch in a preamp and/or attenuator before the mixer, and
an IF preamp after. The RF preamp would use a 2n3886 or 2n5109 bipolar
transistor running with as high a collector current as possible for the
best IP. The IF preamp might use the parallel fets.
For the transmit mixer I'd use one of the MCL canned diode mixers with a
bipolar preamp. The transmit mixer doesn't need to be a high IP type
mixer, we can control the signal levels here to get the best results and
distribute the power gain in previous and prior stages as required.


On 07/06/2011 07:07 AM, Gian, I7SWX wrote:
On Jul 4, 6:31 am, clifford 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
Hi Cliff,

Piero and Tom gave you good comments.

If you need a strong front end your problem is not in the rf
amplifier. You need a strong 1st and 2nd mixer and for this there is
no better solution than the H-Mode Mixer. Having a una upconversion
1st IF, your critical point will be the 2nd mixer that will receive
strong signal amplified by this stage..

If you look at PA3AKE web page you con find info regarding my
simplified version I7SWX 2T H-Mode Mixer (http://
martein.home.xs4all.nl/pa3ake/hmode/2t-hmode.html). This has only 2
transformers and homebrewed, not purchased. You will see the info on
transformers winding, the one with 5 windings may seem difficult but
is not. In low bands you may avoid to have a preamp. Look at the G3XJP
project Pic-A-Star (RSGB RadCom and also reported in the Handbook).

73

Gian
I7SWX

www.hurricaneproject.altervista.org

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

KBa wrote in :

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




Just a quick follow up on the RF amplifier question. Yes I do need a bit
of gain (say 12 dB) before the mixer. One reason is that for many years I
have experimented with low angle radiation on 14 MHz cw. Signals are
often quite weak from the antipodes of NZ (the western mediterranean
area) and I often work them when the band appears dead around local noon.
Fortunately my neighbouring ham is not very active these days.
Anyway for now I am using a cascode JFET amplifier with a relatively high
supply current and this seems adequate. However applying AGC is a bit of
a problem.
Cliff Wright ZL1BDA