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Hello All,

Just wondering what would be the instrument of choice to measure an
IF of around 9.1 MHz, the 400E or the 3400A and, of course, the
reasons?

From the specs they both look like they will do the job, but I am
not sure. Is the 3400A older technology? Does either have a better
reliabiity rating than the other? Easier to calibrate? Uses tough to
find components?

Thanks for your time and thanks to a great group!

Mitch

aquaman8_2001 wrote:

Hello All,
Just wondering what would be the instrument of choice to measure an IF of around 9.1 MHz, the 400E or the 3400A and, of course, the reasons?

From the specs they both look like they will do the job, but I am

not sure. Is the 3400A older technology? Does either have a better reliabiity rating than the other? Easier to calibrate? Uses tough to find components?
Thanks for your time and thanks to a great group!
Mitch

It would help if we knew what you were trying to measure, and why.

-Chuck

Hi Chuck,

I wanted to measure the IF signal levels in a radio that I am trying
to align. Output of one stage needs to be set to 250 mV. Again, the
frequency is at 9 MHz.



Mitch

--- In hp_agilent_equipment@..., Chuck Harris
<cfharris@e...> wrote:

aquaman8_2001 wrote:

Hello All,

Just wondering what would be the instrument of choice to measure

an

IF of around 9.1 MHz, the 400E or the 3400A and, of course, the
reasons?

From the specs they both look like they will do the job, but I am

not sure. Is the 3400A older technology? Does either have a

better

reliabiity rating than the other? Easier to calibrate? Uses tough

to

find components?

Thanks for your time and thanks to a great group!

Mitch

It would help if we knew what you were trying to measure, and why.

-Chuck

Hi Mitch,

Are you trying to peak them, or do you need for them to be
at a specific value? Both of the meters you mention are really
audio meters. That they work up to 10MHz, is just the HP way.

Usually IF's are aligned by either peaking the whole mess as
seen by the AGC, or an AM detector, or using a sweeper with
a special detector. If you attach a 3400 to the IF, it will
load the IF stage so much that your alignment will be wrong.


-Chuck

aquaman8_2001 wrote:

Chuck,

So I guess for that task I am best off with a scope or an RF
voltmeter like the 3404.

Getting back to the 3400A and the 400E what would be the difference
between them, from a task perspective?

Thanks,

Mitch

--- In hp_agilent_equipment@..., Chuck Harris
<cfharris@e...> wrote:

Hi Mitch,

Are you trying to peak them, or do you need for them to be
at a specific value? Both of the meters you mention are really
audio meters. That they work up to 10MHz, is just the HP way.

Usually IF's are aligned by either peaking the whole mess as
seen by the AGC, or an AM detector, or using a sweeper with
a special detector. If you attach a 3400 to the IF, it will
load the IF stage so much that your alignment will be wrong.


-Chuck

aquaman8_2001 wrote:

Hi Chuck,

I wanted to measure the IF signal levels in a radio that I am

trying

to align. Output of one stage needs to be set to 250 mV. Again,

the

frequency is at 9 MHz.

Hi Mitch,

The major difference between the 3400A and the 400E is the way
the AC signal is detected. The 400E uses a common diode, and
the 3400E uses a directly heated thermocouple. So, if your
waveform is a relatively pure sinewave, either will give you
identical results; but, if your waveform is anything else, the
3400A will give you "true RMS", which is the equivalent DC
voltage that would cause the same heating in a resistor, and
the 400E will give you the average of the waveform, multiplied
by the constant that would give the RMS value if it were a sinewave.

What kills you in making RF measurements with the 3400A is the
input impedance, 10M in parallel with *50pf* in the low voltage
ranges, and 10M in parallel with 20pf in the high ranges. The
400E is slightly better with 10M in parallel with 25pf in the
low ranges, and 10M in parallel with 12pf in the high ranges.

The typical scope is better, but it still should be separated
from the stage you are tuning by being downstream as far as
possible. Best is to have isolated test points as permanent
parts of the circuit. Most of the better receivers have these
test points, usually with an emitter follower, or cathode
follower stage for isolation.

-Chuck Harris



aquaman8_2001 wrote:

Good morning John,

Thank you so much for the information. I have several 400E and was
thinking of getting a 3400A, so your description of the differences
was most enlightening.

As to the receiver, the scope method at a point decoupled from the
circuit will be the way I will go.

Thanks again for your time and knowledge,

Happy holidays to the group and peace and happiness to all for 2005,


Mitch

--- In hp_agilent_equipment@..., Chuck Harris
<cfharris@e...> wrote:

Hi Mitch,

The major difference between the 3400A and the 400E is the way
the AC signal is detected. The 400E uses a common diode, and
the 3400E uses a directly heated thermocouple. So, if your
waveform is a relatively pure sinewave, either will give you
identical results; but, if your waveform is anything else, the
3400A will give you "true RMS", which is the equivalent DC
voltage that would cause the same heating in a resistor, and
the 400E will give you the average of the waveform, multiplied
by the constant that would give the RMS value if it were a

sinewave.

What kills you in making RF measurements with the 3400A is the
input impedance, 10M in parallel with *50pf* in the low voltage
ranges, and 10M in parallel with 20pf in the high ranges. The
400E is slightly better with 10M in parallel with 25pf in the
low ranges, and 10M in parallel with 12pf in the high ranges.

The typical scope is better, but it still should be separated
from the stage you are tuning by being downstream as far as
possible. Best is to have isolated test points as permanent
parts of the circuit. Most of the better receivers have these
test points, usually with an emitter follower, or cathode
follower stage for isolation.

-Chuck Harris



aquaman8_2001 wrote:

Chuck,

So I guess for that task I am best off with a scope or an RF
voltmeter like the 3404.

Getting back to the 3400A and the 400E what would be the

difference

between them, from a task perspective?

Thanks,

Mitch