Amateur Radio Report Card

AU GUST 1965
db BELOW
0. 1 MICROVOLT
3
6
9
12
15
IB
20
2 1
23
24
26
2 9
32
35
38
4 1
Tobie I.
MICROVOLTS
.07
.0 5
.035
.025
.0 18
.0 I 3
.0 I
.009
.007
.0063
.00 5
.0035
.0025
.00 18
.00 13
.0009
I n practice, if the shape factor (6 to 60 db )
of the receiver is 2 1
the effective noise band ­
width will be approximately 1.3 times the
6-db bandwid th. If shape factor is between
2 and 10, noise band width will be approximately
equal to the square root of the shape
factor (6 to 60 db) times the 6-db bandwidth.
Few receivers have shape factors
greater than 10.
The approximations quoted earlier ( 1.5
times marked bandwidth for SSB-selectivity
receivers, 3 times marked bandwidth for
others ) are based on these relat'ons. If you're
really interested in calibrating your receiver's
noise bandwid th for using this measurement
technique. however, you might take a converter
and have it measured for noise figure
by the generator technique, then run this
technique backwards to determine the effective
noise bandwidth of your receiver in each
position of the selectivity control.
The technique d escribed here, incidentally,
assumes that no audio filters are used following
the detector. If they are, all results are
off, since the effective noise bandwidth w ill
have been changed in an unpredictable manner
by the audio filters.
However, you can remove the audio filters
from the hooku p for measurement purposes,
determine noise figure, then return the audio
BIters to the circuit and run the measurement
backward to find out your effective noise
bandwidth with filters present. Don't be surprised
if it comes out in the region from 1 to
10 cycles p er second; a good audio filter can
work wonders with weak-signal reception.
For additional details on this technique of
measuring noise figure, you can consult Reference
Data for Radio Engineers, 4th edition,
published by IT&T and available from Radio
Bookshop, or any good radar text.
... K5JKX
HE DIDN'T HAVE
TO GROUND AT ALL
(He owned the linear)
He's well pleased of cou rse, and
proud of that highly potent KW
signa l, as who wouldn't be? Yes,
and perhaps he's just a bit selfsa
tisfied in the knowl edge tha t he
had the foresight to take adva ntage
of a really exceptiona l barga in.
This linear operates on 80-40-20-15,
has bu ilt-in, heavy-duty 117V AC
power supply, costs only 249.50.
The SBE SB-34 pocks p lenty of punch o n 80, 40, 20,
ond 15 meters sidebond with 135 wotts PEP.
(Slig ht ly lo w er on 15). Also covers MARS and out ­
o f-bond OX freq uencies. Bu ilt-in Supply for 12 Vo lt
a nd 117V AC. Send-stcte sw itching ... no re la vs.
Solid· sta te dial calibration. Delta Rece iver tuning.
l ow freq uency drift . Dual-speed tuning.
Feature-w ise . .. Do llar.wise ...
The Bigg est Tro nsceiver Value eve r!
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Ma tchi ng Mike No . 5B2-MIC 5 14.50 Net
Also in stock: SBE Mode l SB2· l A 4-bond
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