Field Strength Of Spurious Radiation (Fcc Rule Part 2.1053) - Furuno FS-2570 Technical Information

Pub. No.: SB-2241
Date : November 1, 2002
3 . 6 FIELD STRENGTH OF SPURIOUS RADIATION (FCC Rule Part
2 . 1 0 5 3 )
3 . 6 . 1 Method of Measurement
The transmitter is connected with measuring equipment as in Fig. 3.6.1.
Supplied with 24 VDC the transmitter is modulated with 2 audio tones 400 Hz and 1800 Hz in
equal level. The input level is adjusted to 10 dB above the level producing PEP output of
250 W.
According to "Reference Data for Radio Engineers", fourth edition, ITT:
Power density P at a distance R (meters) due to power Pt emitted from an isotropic antenna in
free space is expressed:
2 2
P = Pt/4R (W/m )
Power density expressed in field strength E (V/m) is at any point:
2
P = E /120
where 120 is a resistance value of free space.
Therefore,
1/2
E = (120 P)
2 1/2
= (120 Pt/4R )
1/2
= (30 Pt) /R
Field strength due to PEP 250 W at a distance 10 m is:
E =√ 30 x 250 /10
= 8.7 (V/m)
Put 1 µV/m = 0 dBµ
8.7 V/m = 138.8 dBµ (reference level)
With this reference level, field strength of spurious emitted from the FS-2570 is measured b y
Spectrum Analyzer.
Measurement is made for each test frequency within 9 kHz to 300 MHz, especially on
harmonics of carrier frequency Fc, 456.5 kHz (Intermediate Frequency) and its harmonics,
72.4565 MHz (2nd LO frequency) and (72.4565 + Fc) MHz the level is recorded.
Measurement is made for each of 3 planes of the FS-2570 to search the plane where most
spurious radiation is found.
66
Page 40 of -
-