EMRFD Message Archive 1241
Message Date From Subject 1241 2007-12-17 20:35:25 anguria2004 Hybrid Cascode IF Amp
Anyone else building the W7ZOI/WA7MLH HYCAS amp kitlet?
I have a couple of more hours to go, but that's only because I am slow
and measure everything before installing. Totally smooth so far. A
lot of fun for $25.
I am building it as described for 9 MHz, but then will put it down on 4
Mhz. I'll change the input L network, but should I also scale the
collector inductances of L2, L3, T1 and L4?
I'll probably just change the inductors back to 120 uH on 43 material
and see how it goes.
Mark, KE7MSU
Lake Oswego, Oregon1242 2007-12-18 02:03:41 Omar Shabsigh Re: Hybrid Cascode IF Amp
Good morning. Could you please tell me where I can find information about W7ZOI/WA7MLH HYCAS amp kitlet??
Best 73
Omar YK1AO
----- Original Message -----
1243 2007-12-18 06:16:30 Robert Cerreto Re: Hybrid Cascode IF Amp
I built the amp from the schematic and found that other than the input network, it was very wide banded. I don't recall a definitive measurement at 4Mhz. But I do remeber that it had good gain in that area.I used FT-37-43 cores for the interstage inductors. and the inductance was originally quite high when I made the quick measurement, allowing good lower freqeucy response. About the same time Wes noted possible stabilityproblems on his site, I had to change the inductance from 150uh to about 50uh for stability reasons. My amp was showing a tendency to oscillate aroun 5-6Mhz.Lowering the overall gain solved that. All those DB's aren't much good if the thing decides to oscillate! If you don't have an answer by the end of the day, I will look at it more closely when I get home from the company store tonight.
73, Bob
WA!FXT
anguria2004 <mark.mccarthy@comcast.net> wrote:
Hello,
Anyone else building the W7ZOI/WA7MLH HYCAS amp kitlet?
I have a couple of more hours to go, but that's only because I am slow
and measure everything before installing. Totally smooth so far. A
lot of fun for $25.
I am building it as described for 9 MHz, but then will put it down on 4
Mhz. I'll change the input L network, but should I also scale the
collector inductances of L2, L3, T1 and L4?
I'll probably just change the inductors back to 120 uH on 43 material
and see how it goes.
Mark, KE7MSU
Lake Oswego, Oregon
---------------------------------
Never miss a thing. Make Yahoo your homepage.
[Non-text portions of this message have been removed]1244 2007-12-18 13:08:20 Ed - K9EW Re: Hybrid Cascode IF Amp
In case no one has given you the information, take a look at
http://www.ka7exm.net/.
73,
ed - k9ew
www.k9ew.us1245 2007-12-18 13:08:30 john lawson Re: Hybrid Cascode IF Amp
Below is Wes's website with the Kitlet lnformation. I
have built it and it works very nicely. Mine is used
with a 9 Mhz filter...John, K5IRK
http://w7zoi.net/hycas-pcb.html
1246 2007-12-19 09:32:47 Roger Hayward Hybrid Cascode IF Amp / Article reprint available
Information on the IF amplifier can be found in 3 locations:
December 2007 QST: The IF amplifier is described in QST.
w7zoi.net : Wes has some comments, including some changes to the
circuit which will improve the stability of the circuit.
ka7exm.net : Roger (whoops, that's me!) is offering components and PC
boards to assist you with your construction efforts.
IN ADDITION, The ARRL has graciously provided an article re-print of
the original IF amplifier article. This is posted1248 2007-12-19 15:06:25 Wes Hayward Re: Hybrid Cascode IF Amp
There should be no need to change the components other than the input
network when building the hybrid cascode amplifier from the QST
article. There is plenty of gain down at 4 MHz. That is probably
closer to a frequency of highest gain than is 9 MHz with the
inductors that are in the "kitlets" that Roger is distributing. Be
sure to back off on overall gain with the modifications mentioned on
the web, especially if any instabilities are observed.
Let me extend a Happy Holiday Seas1249 2007-12-20 11:32:05 Juanjo Pastor Re: Hybrid Cascode IF Amp
I have been trying to contact Roger at his gmail.com address but my messages
got bounced everytime I sent them. Please, Roger, drop me a mail. Holiday
greetings for everybody in the group and especially to Wes and Roger!
73, 72 de Juanjo, EC5ACA. EA-QRP #104, G-QRP #9742, QRP-L #1662,
FP #899.
Juanjo Pastor
C/San Roque, 4-1ยบ
46460 Silla
SPAIN
e-mail: ec5aca@gmail.com
web: http://es.geocities.com/ea5chq
web del club: http://www.eaqrp.com
Tel.: +034 96 120 17 67
Movil: 651 35 35 11
----- Original Message -----
1252 2007-12-21 17:36:08 Mike Brainard Re: Hybrid Cascode IF Amp
I wanted to mention one very slight difference between the QST
schematic and the HYCAS board layout. For the PNP differential
amplifier pair, bias resistor R19 is shown in QST connected to the base
of Q7. On the HYCAS board it is connected to the base of Q8. It works
essentially the same either way. This difference is only important in
troubleshooting a non-working differential amp.
AD5RJ1253 2007-12-23 17:13:01 Wes Hayward Re: Hybrid Cascode IF Amp
OK, I confess. I did it and I didn't tell. When I was doing the
layout for the board, it worked well to put one resistor on each side
of the T1 output link. I thought "Should I change it?" I decided
not to bother, for I didn't think that folks would notice. Also, it
really has absolutely nothing to do with the AC or RF performance.
The link is a short circuit for DC.
But Mike is now the 2nd pers1255 2007-12-24 14:16:00 Allison Parent Re: Hybrid Cascode IF Amp
I'd suggest posting a "as built" schematic on your site that matches
the board. I saw the resistor location and recognized the sense
of locating where it was. It's helpful to have a 1:1 circuit to
board reference especially for troubleshooting or for people that
may modify the design.
I've finished testing mine. Several items were tested one being
stability. I looked at it without the series resitor on diff amp
emitters to see it in action. Source was a 50ohm to 450ohm
transformer with a 10db pad and I did see the instability at max
gain. The output was coax feed to a 50ohm rf milliwattmetter. I
explored by trial bypassing of several places to see it there were
sneak paths and found no improvement. Next step was small shields
made of 2mil copper shim stock over the collector chokes and this
did impact stability for the better. I also found that any means
that lowered gain overall also had the same effect (improved
stability). Not a surpize with over 60db of gain. I ended up
with resistor in series with C12. Works well in that form.
Next step is a simple "S" meter circuit, the likely candidate is
a diff pair of PnP transistors with meter between collectors. The
connect points would be transistor bases monitoring the AGC
setpoint (r32 wiper) and Q9 emitter. I have to proto it and see
it work. Whatever way the metering is done the circuit will have
a few diodes and resistors to make the scale something more log.
Next step is a high level front end and a decent filter.
Allison
1256 2007-12-24 20:07:18 Wes Hayward Re: Hybrid Cascode IF Amp
Good idea. I'll get going on a suitable "as built" schematic after
the holidays.
Glad to hear that you got it working without any difficulty. (We
kinda figured it would not be a problem for you, hi.) Great on the
stability observations. That is a lot of gain in one place and
those inductors hanging out there in the air don't help. But the
temptati1257 2007-12-24 20:33:43 Allison Parent Re: Hybrid Cascode IF Amp
Compared to some FM IFs I've done where the gain can easily
exceeed 80db or more this one is very tame.
I think the desire to use discretes is many are intimidated
by opamps. I use opamps but rather than deal with dead
bugging a DIP transistors can be easier.
The use of a difamp is old and really masks the OpAmp
situation as it's the same core circuit anyhow. The issue
is simple, measure a voltage with an offset and not loading
the measured point greatly. The easy part is the voltage
is large and the offset is within a diode junction or two
of the reference point (wiper of the IF gain pot). The
optimal design in my book is one where changes in the IF
gain setpoint does not cause a zero shift on the readout
of the AGC voltage.
Happy Holidays
Allison