Service Manuals, User Guides, Schematic Diagrams or docs for : Agilent journals 1954-08
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HEWLETT' PACKARD
JOURNAL
TECHNICAL INFORMATION FROM THE -hp- LABORATORIES
Vol.5 No. 12
UBLISHED BY THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA AUGUST, 1954
Advanced Performance in
Two New VHF Signal Generators
IN ORDER for an amplitude-modulated sig have modulation applied to it. As a result,
nal generator to be suitable for testing high- modulation voltages do not react on the oscil
performance receivers, one of its most important lator and incidental f-m is of a low order.
requirements is that it have a low order of The MOPA circuit arrangement has quite
incidental f-m. The reason for this is that ap naturally been followed in the design of two
preciable f-m in a signal generator usually new signal generators which have been devel
causes serious errors in evaluating receiver per oped for the r-f to lower uhf range. The more
formance and further leads to misalignment of technically refined of these new generators, the
the receiver. Although ordinarily not present Model 608D, operates from 10 to 420 mega
in troublesome proportions in lower frequency cycles, is capable of sine-wave or pulse modu
generators, incidental f-m tends to be a signifi lation, delivers a maximum of 0.5 volt across
cant problem in vhf generators, especially when 50 ohms, and incorporates a 0.01%- tolerance
inelegant modulation methods are used. crystal calibrator to permit unusually high accu
In the design of -hp- signal generators, free racy of output frequency.
dom from incidental f-m has always been an The second generator, the Model 608C, oper
important consideration. It has led to the use of ates from 10 to 480 megacycles and provides a
master-oscillator-power-amplifier type designs maximum output of 1 volt across 50 ohms. It is
for the -hp- generators that operate in the r-f, generally similar to the Model 608D except that
vhf and lower uhf regions. The advantage of it does not include a crystal calibrator and that
the MOPA arrangement is, of course, that the some of its characteristics have not been refined
r-f oscillator circuit in the generator does not to such a high degree as in the 608D.
R-F SECTION
Circuit arrangements for the two
new generators are shown in block
form in Fig. 2. The r-f oscillators in
both generators are essentially the
same and use type 5675 pencil triodes
operating in modified Colpitts cir
cuits. In both generators the oscillat
ors cover their respective ranges in 5
bands as shown in the accompanying
table. Each band has a calibrated
scale length of approximately 10
inches, giving an overall scale length
Fig.l. 608C to the popular -hp- Model 608A-B's, new -hp- Models 608C of some 50 inches for the complete
(left) and 608D Signal Generators cover 10 to 400-plus megacycle range.
MOPA type circuits are used in both instruments. range. The tuning capacitors are de-
P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 4 H E W L E T T - P A C K A R D C O .
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