开云体育

Lets go back to the basics,
A spectrum analyzer basically is a swept receiver, in the case of the 8553 you have three conversion steps to reduce the input signal to 3MHz IF, the first LO normally is swept by a ramp, the amplitude of the ramp determines the sweep width or span while the DC offset of the Ramp normally determines the start frequency of your sweep.
The tracking generator is basically a "reversal" of your spectrum analyzer, you take the LO signals and mix them with a Fixed lo that represents the IF used, amplify the resulting signal and level it, the signal frequency will track with the frequency of your spectrumanalyzer, now if you insert a filter for example you will be able to measure the filter characteristics !
Now to the markers, the X axis of your analyzer can be scaled in a voltage/div, lets say you sweep the full band of 0-110MHz, your DC offset will be O and your ramp will be 10Vp, now you have 11MHz/Volt, lets assume you desire a marker at 55MHz , 55MHz corresponds to 5Vp on your ramp, you now take a comparator and run the ramp on one input and the 5V reference on the other whenever the two match you get a pulse, all you need to do now is to route the pulse back into your analyzer and use it to either blank the trace for a short period of time or intensify it, so now you got a marker on your screen even without any RF !
now at last you want to know the marker frequency, you have two ways to skin this cat, you can either use a voltmeter to measure your reference voltage scale it and display it on a digital display (this however is not how the 8443 does it) or you can use a frequency counter and connect it to the RF output, now since you only want the marker count you only trigger the counter whenver you get the marker pulse and at the same time stop the sweep for a brief moment to allow the counter to aquire the signal, now you counted your marker !
In this system the only function that will not work if the RF signal is gone is in fact the frequency counter for your marker function ! you will however always get a marker blip on your display whether you have RF or not !
If you look closely at your control cable that connects the 8443 with the 141T you will notice that beside the coax contacts you also have regular Contacts, those contacts carry the control signals, you will also notice that you have more coax contacts than LO signals, this is because one of the coaxes carries your sweep ramp from your 141T mainframe.
I suggest you download the 8443 manual and study the functions, it contains a good overall circuit description as well as block diagrams that will help you understand the functionality

"David C. Hallam" <dhallam@...> wrote:
Now I am getting confused.

The spectrum analyzer screen has a line designated CENTER FREQUENCY. As you
turn the frequency knob on the 8553B RF section to move a signal peak to
coincide with this line, you can read the frequency of the signal from the
linear scale on the 8553B.

When the 8443A tracking generator is connected to the 141T system, it
generates a marker on the CENTER FREQUENCY line of the 141T display. As
above, when you move a signal peak to coincide with this line and place the
marker at the top of the peak, the 8443A will display the frequency of the
signal.

The marker is on the CENTER FREQUENCY line of the screen all the times,
input signal or no input signal.

What is happening is there is no display of frequency on the 8443A at any
time. Even when the marker is centered on the signal peak.

The 8443A is also capable of being used as a stand alone frequency counter.
If I connect my signal generator to the 8443A in this mode, the 8443A will
display the frequency of the signal generator output.

David