My original question was to see if anybody had any experience with the "no
Tx audio" problem. As it turned out, there was a bad 330uF 10V electrolytic
cap that was causing the problem. As it turned out, this unit turned out to
be another unit that was
"peaked and clipped" by somebody who didn't know what they were doing. In
other words, another piece of eBay junk.

Pete

"Frank Gilliland" wrote in message
...
On Sun, 25 Feb 2007 16:23:27 -0600, "Pete KE9OA"
wrote in
:

There is no such thing as an intended frequency. Now, if you said that if
a
resistor is used, taking into account its limitations. Must we continue
this
silly bantering?


My apologies. I'll rephrase:

When a resistor is used within it's intended operating frequency
range.....

When a resistor is used below the frequency where it no longer behaves
like a resistor.....

When a resistor is used in the frequency range for which it was
designed.....

Better?

And if you don't like "silly bantering", why are you in this group?

I like to use 0805 series, at higher frequencies, I see 0603 and smaller
sizes being used. As far as carbon comp resistors, they are the best
through-hole components for RF, at least up to a certain point. True, they
can and do change value over the years, and they can absorb moisture.

Pete

"james" wrote in message
...
On Sat, 24 Feb 2007 18:01:09 -0600, "Pete KE9OA"
wrote:

+++Resistors can have complex impedances, especially film resistors.
Carbon
+++film resistors can get by up to 30MHz or so, and metal film resistors
+++shouln't be used above 10MHz. The problem with these devices is that
they
+++consist of a sprial etched resistance material that has a fair amount
of
+++reactance as you go up in frequency.
+++Carbon composition resistors are preferable in RF applications, but
even
+++their lead length becomes too reactive at higher frequencies.
+++Nowadays, we use 0603 or smaller size components at higher frequencies.
0402
+++geometry is presently being used at higher frequencies, with 0201 size
soon
+++to become the norm. This is what I have been working with for the last
+++couple of years.
+++
+++Pete
+++
*************

And carbon composition should be avoided. They absorb moisture and
change resistance with time. I have seen to many 100K carbon comps
measue around 60K with time. I would aviod them like the plague.

I have worked with chip components for over 20yrs. I stay away from
the samllest one unless the board density constraints or the design
dictates it.

james
james




+++"Frank Gilliland" wrote in message
om...
+++ On Mon, 19 Feb 2007 19:12:33 GMT, james wrote
+++ in :
+++
+++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland
wrote:
+++
++++++Conjugate match is needed for maximum power transfer.
++++++
++++++
++++++IMPEDANCE match... for maximum power transfer. A 'conjugate'
match is
++++++when the impedances are complex, which isn't always the case.
+++***********
+++
+++I have found that it is rare in the real world that impeadances are
+++not complex. Outside transimission lines, there is little that is not
+++complex.
+++
+++
+++ You just said that resistors have complex impedance and transmission
+++ lines are flat.
+++
+++
+++ Then again when you conjugate match, the imaginary part of
+++the complex impedances is nulified and you are then left with the
real
+++part.
+++
+++
+++ Reactances don't just disappear. They create a current between the
+++ source and load that must be assessed to see if it is going to cause
+++ any problems. Sometimes it doesn't and sometimes it does.
+++
+++
+++
+++

From the above statement, I can tell that you have very little experience
with doubly balanced mixers, especially the ones from Mini-Circuits.


You're right. I ran some of their stuff through the bench many years
ago and was disappointed, so I never used it. As for size, Analog
Devices has been making some remarkable stuff in the last few years.

I have worked with some of their newer stuff, and it has been very good. AD
got their act together pretty well, in the RF arena.
The Analog Devices AD831 isn't a bad design; it does have a good IP3, but in
order to reach the NF of a Mini-Circuits SRA-3 however, you need to have a
preamplifier ahead of it. With its 12dB NF, it isn't a bad mixer for HF use
up to 30MHz. I had started a receiver design using the 831, but things got
so busy at work that I shelved that project for awhile.


The
LAVI-XXX series of mixers have IP3s in the +33 to +40dBm range.


You used dB before, which I assumed was carrier attenuation. Still,
I'm not impressed.

I thought the only reference to dB was port to port isolation and SSB
conversion loss.


The only
type of discrete mixer that can even come near this type of performance is
something that uses either a quad JFET ring, a quad CATV bipolar ring, or
a
dual power FET type that uses something like the Siliconix VN66. Your
typical balanced dual JFET mixer, as used in some of the Yaesu and Icom
transceivers will achieve IP3s in the +10 to +15dBm range, which isn't
bad.
This is without having the preamp switched in.
Now, to even be able to measure that type of performance, you need to have
all of your RF sources very clean.


Exactly! That's why I pointed out those numbers are "lab numbers". If
you want to get some realistic numbers you have to test it under
realistic conditions, which isn't that hard. The only drawback is that
the numbers will be relative; i.e, it's a comparison test against
other circuits. But if you do you will find that what I'm saying is
true -- discretes perform much better. And yes, you have to carefully
match the curves. This added labor, along with higher assembly costs
and parts counts, are the primary reasons why discretes are rejected
over mini-bricks; it rarely has anything to do with performance.

I agree on those points. Unless the LO in the actually is actually filtered
to the point where all higher terms are at least -65dBc, that performance
won't be realized. The manufacturers I worked for over the years were quite
happy with -25dBc for the 2nd harmonic of the LO.


It also serves as a buffer to the mixer, which is essential for
reducing mixer IMD. The RF amp is generally a good idea.

The RF amp will not reduce IMD..........it will actually degrade the IMD
performance of the mixer by the amount of gain that the RF amp provides.
It
is very easy to see this if you are making IP3 measurements on a mixer.
Add
10dB of gain ahead of that mixer, and IP3 degrades by 10dB.


I can see that you are locked into a voltage-only mode. Feed your
mixer under test with signals of varying impedance. I think you will
be suprised, if not shocked.

You do make a good point; an unconditionally stable low gain RF amplifier
will satisfy this requirement. I have done the measurements that you
mention, and I have noted some level of disparity between real world
conditions and manufacturers' specs. I know................too many
manufacturers play the "numbers game". As long as they stick to the same
standards, one can use these numbers to initially select a product but the
devices still need to be characterized before those numbers are actually
believed.

Pete

On Sun, 4 Mar 2007 11:09:00 -0600, "Pete KE9OA"
wrote in
:

My original question was to see if anybody had any experience with the "no
Tx audio" problem. As it turned out, there was a bad 330uF 10V electrolytic
cap that was causing the problem.


15 volt?


As it turned out, this unit turned out to
be another unit that was
"peaked and clipped" by somebody who didn't know what they were doing. In
other words, another piece of eBay junk.


Too many of those out there.

On Sun, 4 Mar 2007 11:09:00 -0600, "Pete KE9OA"
wrote:

+++My original question was to see if anybody had any experience with the "no
+++Tx audio" problem. As it turned out, there was a bad 330uF 10V electrolytic
+++cap that was causing the problem. As it turned out, this unit turned out to
+++be another unit that was
+++"peaked and clipped" by somebody who didn't know what they were doing. In
+++other words, another piece of eBay junk.
+++
+++Pete
********

Yep, Seen many an electrolytic go bad. Especially in power supplies.
Heat is the enemy of electrolytics.

As for EBAY CB radios, mostly useless other than parts.

james

On Sun, 4 Mar 2007 11:23:03 -0600, "Pete KE9OA"
wrote in
:


From the above statement, I can tell that you have very little experience
with doubly balanced mixers, especially the ones from Mini-Circuits.


You're right. I ran some of their stuff through the bench many years
ago and was disappointed, so I never used it. As for size, Analog
Devices has been making some remarkable stuff in the last few years.

I have worked with some of their newer stuff, and it has been very good.


I'll have to run some of the new stuff across the bench.


AD
got their act together pretty well, in the RF arena.
The Analog Devices AD831 isn't a bad design; it does have a good IP3, but in
order to reach the NF of a Mini-Circuits SRA-3 however, you need to have a
preamplifier ahead of it. With its 12dB NF, it isn't a bad mixer for HF use
up to 30MHz. I had started a receiver design using the 831, but things got
so busy at work that I shelved that project for awhile.


Call me old-fashioned but I still prefer discretes.


The
LAVI-XXX series of mixers have IP3s in the +33 to +40dBm range.


You used dB before, which I assumed was carrier attenuation. Still,
I'm not impressed.

I thought the only reference to dB was port to port isolation and SSB
conversion loss.


Port to port isolation or carrier rejection, whatever you want to call
it..... you can easily get 60 dB or better using discretes. Heck, some
of the old DSB-SC tube rigs were even designed to mix in a -power-
stage!

Anyway, you used dBm in one post and dB in another; not the same
thing.


The only
type of discrete mixer that can even come near this type of performance is
something that uses either a quad JFET ring, a quad CATV bipolar ring, or
a
dual power FET type that uses something like the Siliconix VN66. Your
typical balanced dual JFET mixer, as used in some of the Yaesu and Icom
transceivers will achieve IP3s in the +10 to +15dBm range, which isn't
bad.
This is without having the preamp switched in.
Now, to even be able to measure that type of performance, you need to have
all of your RF sources very clean.


Exactly! That's why I pointed out those numbers are "lab numbers". If
you want to get some realistic numbers you have to test it under
realistic conditions, which isn't that hard. The only drawback is that
the numbers will be relative; i.e, it's a comparison test against
other circuits. But if you do you will find that what I'm saying is
true -- discretes perform much better. And yes, you have to carefully
match the curves. This added labor, along with higher assembly costs
and parts counts, are the primary reasons why discretes are rejected
over mini-bricks; it rarely has anything to do with performance.

I agree on those points. Unless the LO in the actually is actually filtered
to the point where all higher terms are at least -65dBc, that performance
won't be realized. The manufacturers I worked for over the years were quite
happy with -25dBc for the 2nd harmonic of the LO.


And then they moved on to designing CB amps?


It also serves as a buffer to the mixer, which is essential for
reducing mixer IMD. The RF amp is generally a good idea.

The RF amp will not reduce IMD..........it will actually degrade the IMD
performance of the mixer by the amount of gain that the RF amp provides.
It
is very easy to see this if you are making IP3 measurements on a mixer.
Add
10dB of gain ahead of that mixer, and IP3 degrades by 10dB.


I can see that you are locked into a voltage-only mode. Feed your
mixer under test with signals of varying impedance. I think you will
be suprised, if not shocked.

You do make a good point; an unconditionally stable low gain RF amplifier
will satisfy this requirement.


Hence my recommendation to use a low-impedance front end.


I have done the measurements that you
mention, and I have noted some level of disparity between real world
conditions and manufacturers' specs. I know................too many
manufacturers play the "numbers game". As long as they stick to the same
standards, one can use these numbers to initially select a product but the
devices still need to be characterized before those numbers are actually
believed.


I won't even use a 2-cent resistor until I destroy it on the bench
first. A lot of the manufacturer specs look really good on paper but
don't mean squat beyond the ideal conditions of a lab test. Even a
supposedly identical component made by different manufacturers will
behave differently in the actual circuit, especially under failure
analysis (which can be a very expensive lesson if not learned before
designing or repairing power equipment..... don't ask!).

It was actually a 10V unit. I don't know why they would use something like
that either. All I've got to do is isolate the problem with whatever sets
the parameters for AM mode. It receives fine in AM mode, transceives fine in
SSB mode. Looking at the schematic, I saw a 220 Ohm resistor that is
switched in for biasing the output stage for SSB. In the AM mode, the mode
switches bypasses this resistor. Could be a bad mode switch. I have been
working 60+ hours every week, so I get about an hour each weekend to work on
this thing. Unless they send me out to Singapore for
awhile....................

Pete

"Frank Gilliland" wrote in message
...
On Sun, 4 Mar 2007 11:09:00 -0600, "Pete KE9OA"
wrote in
:

My original question was to see if anybody had any experience with the "no
Tx audio" problem. As it turned out, there was a bad 330uF 10V
electrolytic
cap that was causing the problem.


15 volt?


As it turned out, this unit turned out to
be another unit that was
"peaked and clipped" by somebody who didn't know what they were doing. In
other words, another piece of eBay junk.


Too many of those out there.

"Frank Gilliland" wrote in message
...
On Sun, 4 Mar 2007 11:23:03 -0600, "Pete KE9OA"
wrote in
:


From the above statement, I can tell that you have very little
experience
with doubly balanced mixers, especially the ones from Mini-Circuits.


You're right. I ran some of their stuff through the bench many years
ago and was disappointed, so I never used it. As for size, Analog
Devices has been making some remarkable stuff in the last few years.

I have worked with some of their newer stuff, and it has been very good.


I'll have to run some of the new stuff across the bench.


AD
got their act together pretty well, in the RF arena.
The Analog Devices AD831 isn't a bad design; it does have a good IP3, but
in
order to reach the NF of a Mini-Circuits SRA-3 however, you need to have a
preamplifier ahead of it. With its 12dB NF, it isn't a bad mixer for HF
use
up to 30MHz. I had started a receiver design using the 831, but things got
so busy at work that I shelved that project for awhile.


Call me old-fashioned but I still prefer discretes.


The
LAVI-XXX series of mixers have IP3s in the +33 to +40dBm range.


You used dB before, which I assumed was carrier attenuation. Still,
I'm not impressed.

I thought the only reference to dB was port to port isolation and SSB
conversion loss.


Port to port isolation or carrier rejection, whatever you want to call
it..... you can easily get 60 dB or better using discretes. Heck, some
of the old DSB-SC tube rigs were even designed to mix in a -power-
stage!

Anyway, you used dBm in one post and dB in another; not the same
thing.


The only
type of discrete mixer that can even come near this type of performance
is
something that uses either a quad JFET ring, a quad CATV bipolar ring,
or
a
dual power FET type that uses something like the Siliconix VN66. Your
typical balanced dual JFET mixer, as used in some of the Yaesu and Icom
transceivers will achieve IP3s in the +10 to +15dBm range, which isn't
bad.
This is without having the preamp switched in.
Now, to even be able to measure that type of performance, you need to
have
all of your RF sources very clean.


Exactly! That's why I pointed out those numbers are "lab numbers". If
you want to get some realistic numbers you have to test it under
realistic conditions, which isn't that hard. The only drawback is that
the numbers will be relative; i.e, it's a comparison test against
other circuits. But if you do you will find that what I'm saying is
true -- discretes perform much better. And yes, you have to carefully
match the curves. This added labor, along with higher assembly costs
and parts counts, are the primary reasons why discretes are rejected
over mini-bricks; it rarely has anything to do with performance.

I agree on those points. Unless the LO in the actually is actually
filtered
to the point where all higher terms are at least -65dBc, that performance
won't be realized. The manufacturers I worked for over the years were
quite
happy with -25dBc for the 2nd harmonic of the LO.


And then they moved on to designing CB amps?


It also serves as a buffer to the mixer, which is essential for
reducing mixer IMD. The RF amp is generally a good idea.

The RF amp will not reduce IMD..........it will actually degrade the IMD
performance of the mixer by the amount of gain that the RF amp provides.
It
is very easy to see this if you are making IP3 measurements on a mixer.
Add
10dB of gain ahead of that mixer, and IP3 degrades by 10dB.


I can see that you are locked into a voltage-only mode. Feed your
mixer under test with signals of varying impedance. I think you will
be suprised, if not shocked.

You do make a good point; an unconditionally stable low gain RF amplifier
will satisfy this requirement.


Hence my recommendation to use a low-impedance front end.


I have done the measurements that you
mention, and I have noted some level of disparity between real world
conditions and manufacturers' specs. I know................too many
manufacturers play the "numbers game". As long as they stick to the same
standards, one can use these numbers to initially select a product but the
devices still need to be characterized before those numbers are actually
believed.


I won't even use a 2-cent resistor until I destroy it on the bench
first. A lot of the manufacturer specs look really good on paper but
don't mean squat beyond the ideal conditions of a lab test. Even a
supposedly identical component made by different manufacturers will
behave differently in the actual circuit, especially under failure
analysis (which can be a very expensive lesson if not learned before
designing or repairing power equipment..... don't ask!).



I do understand your thinking.........Maxim used to love us to do their
"beta testing" on their new devices. I don't remember using dB and dBm in
the same context. It must have been late.......probably a typo on my part.
Just 100 more hours, and I can undo everthing that the other guy did to my
fine radio!!!!!!!!!!!!

Pete