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ADCs require a 2.5 MHz clock signal from the CPU board. hey convert the 27.778 kHz signal
into digital data, which is then sent to the digital signal processor (DSP) on the A2 CPU board.
Di erences Between the HP 8711C/12C/30A and HP 8713C/14C (1300 MHz
vs 3000 MHz)
he HP 8713C/14C analyzers are very similar to the HP 8711C/12C/30A. hey all share the
same front panel, CPU, fractional-N/reference, power supply, display, and rmware. he
two major di erences are in the source and receiver. Refer to the block diagram of the
HP 8713C/14C for an overall view of these two assemblies.
As in the HP 8711C/12C/30A, the source outputs both RF and LO signals that are separated by
27.778 kHz, however the methods used to generate these signals are slightly di erent. In the
receiver, the re
ection port coupler has changed signi cantly. It is a separate dual-directional
coupler microcircuit which provides much better accuracy and stability than can be achieved
using on-board separate components at 3000 MHz. his also allows the same receiver board to
be used for both 50
and 75
instruments. Only the coupler assembly and a jumper setting are
di erent between the two versions.
HP 8713C/14C A4 Source Assembly
he A4 source is designed with four di erent frequency bands:
Band 1= 0.3-1910 MHz
Band 2= 1910-2310 MHz
Band 3= 2310-2620 MHz
Band 4= 2620-3000 MHz
he di erences between bands 2, 3, and 4 are only lter changes. Di erent lters are inserted
or removed in the RF and LO signals to minimize spurs. he major change is between bands
1 and 2.
In band 1, below 1.91 GHz, the source is very similar that of the HP 8711C/12C/30A. However,
the fractional-N input is rst divided by 7 instead of 4, the source LO is divided by 512 instead
of 256 and the RF1 signal is 2339.777778 instead of 2340 MHz. his gives a Fractional-N to RF
output frequency formula of:
RF
= (Fractional-N
ut
(all frequencies in MHz)
his is very similar to the HP 8711C/12C/30A formula:
RF
= (Fractional-N
ut
he HP 8713C/14C fractional-N input frequency will vary from about 32 to 58 MHz as opposed
to the HP 8711C/12C/30A variation of about 36.6 to 57 MHz. In both cases the pulse swallow
circuitry maintains the RF2 signal to be 27.778 kHz below the RF1 signal so that the nal LO
will be 27.778 kHz above the RF, thus generating the proper IF.
In bands 2 through 4, above 1.91 GHz, the RF1 and RF2 signals are divided by 2 to provide an
RF1 frequency of 1169.777778 MHz (the ratio is not exactly 1/2 due to di erences in the way
the pulse swallow circuitry works). he formula for RF output frequency now becomes:
RF
= (Fractional-N
ut
he Fractional-N signal now varies from about 42 to 57 MHz to provide the 1910 to 3000 MHz
RF output in bands 2 through 4. his means that during a full band sweep of .3 to 3 GHz, the
fractional-N output will rst sweep from about 32 to 58 MHz, then reset to 42 MHz, and sweep
again up to 57 MHz.
2
0
512/7)
2339.777778
2
0
256/4)
2340
2
0
512/7)
1169.777778
Theory of Operat on
6-7
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