HP 8648C Question

[MotoDog]

I got myself a Christmas present on eBay.  An HP 8648C RF Signal Generator.

When I put my Rigol DSA 815 spectrum analyzer on the 10 Mhz reference on the back (BNC) with a 20 dB atten. , I get
-7 db signal at 10.033333 Mhz.  Not 10 Mhz exactly?

Anyone know or got a manual?

Thanks
Mike

[KJDS]

What makes you think that the 10MHz ref is wrong and not the Rigol?

What does the Rigol think of what comes out the front? at 10MHz and also at higher frequencies?

[MotoDog]

Well, I have a 50 Mhz Oscillator (the can type on 5V) on a breadboard.  The SA marker is reading 50.001666?

I am trying to make sure the HP RF Generator is OK.  It was advertised as in good working condition.  It seems to work fine,
and then sometimes intermittent or I am having cockpit problems.   The 10 MHz out the back I found off 10 MHz?
It may not matter?  I think things are probably OK.  I will get a freq. counter some day or maybe try comparing to WWV on
a receiver.

I sure like having the SA and the Generator!  I have been playing with transmitting and receiving with Arduino and 433 MHZ Modules.


Mike, WA6ISP
Crestline, Ca.
 

[TheSteve]

I'd expect the Rigol to be closer then that and would suspect the 10 MHz reference. Without a true known reference though you will never know.

[G0HZU]

What span are you using on the Rigol when measuring frequency?

xx.001666MHz and xx.033333MHz suggest that you are using a very wide span because these look to be bin size limitations (i.e. they look like neat fractions) rather than accurate measurements of frequency.

Try zooming down in span size or better still use a frequency counter to measure the sig gen reference.

The 10MHz reference in the HP sig gen is probably just HP's standard low cost 10MHz reference but it is unlikely to be more than 20ppm off frequency even if it hasn't been adjusted in many years so this would be a 200Hz error at 10MHz.

[MotoDog]

Yes, I have wondered about the odd freq shown.  I do see difference when I push AUTO, and let the SA do the setup.

I also just got a DS1054Z scope.  It has a frequency counter function.  It matches the HP 8648.  It seems to stay the same
no matter what the horiz. sweep is set for.  Might be a real frequency counter?

So, I think you are correct, it depends on the span on the SA.

Thanks
Mike, WA6ISP