3.4. Modelamiento y simulación del sistema de control
3.3.3. Simulación del sistema de control
fe r r i t e was v e ry b r oa d ly t uned and c ou p l e d t o a p r e -
amp l i fi e r w h i c h f i r s t mat c he d i t t o t h e c o- a x i a l l i ne and
sec ond provided a t rap to re jec t the l ocal rad i o stat i on
( 94 0 kH z ) . I n ad d i t i on the f e r r i t e s w e r e provided w i th
e l e c t r o s t a t i c s c r e ening t o m i n i m i s e any l oca l p i c k-up .
The u s e o f t w o aerials prov i d e s the ne c e ssary
means by which s i gna ls of t he same fre quency might .be
ident i fi e d by t h e i r angle of a r r i va l . For any one s i gnal
arr i v i n g the pha s e d i f f e r e n c e b e t w e e n t he s i gnals as
ava i la b l e from the two � e r ials i s a measure of t he angle
of ar r ival of the s i gna l . N o one signa l can be s e le c t e d
i n pre f e r enc e t o a l l ot hers , b u t any one s i gnal may b e
r e j e c t e d . This r e qu i r e s phase shi ft ing , amplit ude mat c hing
and a c ompari s on ampl i f i e r . A block d iagram o f t h e ac t ual
s y s t e m u s e d i n t his experiment is s hown i n f i gure i x .
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ix :
OUTPVT
A b l oc k d iagram of t he sys t e m u s e d in t his e xpe rime nt .
- 4 5 -
3-2 : o f t he wave .
During the day t i me when only t he ground wave i s
pre s e nt in a n y s t rength t h e preset pha s e sh i ft i s swit c h e d out a n d t h e var i ab l e phas e shi ft a n d t h e variable at t e nuators
are ad j us t e d unt i l the output from t he di f f erenc e ampli fier
i s ( i deally ) ze r o . I n prac t i c e the gr ound wave i s r e duc e d
by 40 d B f r om t h e s i gnal avai lable a t one aerial e l e ment .
The h or i z ont a l gr ound wave si gnal arr i vi n g at aerial t w o
lags t h e s i gnal at a eri al one b y 360 D/� de gr e e s . The variable pha se sh i ft ha s advan c e d t h e aerial t w o si gnal by this am ount and a l s o c ompensat e d f or any d i f fe r e nc e b e t w e e n
t h e t w o channels u p t o the d i f f e r e n c e ampl i fi e r . The
response of the aerial sys t e m is now o f the f orm shown in
fi gur e x . Thi s i s bas ic ally the me thod u s e d t o obtain t h e
s k y wave . The int e r -aerial spac i n g u s e d was 0 . 1 1 km •
� As
t he dire c t i on o f t he groun d wave i s c onst ant day and ni ght any s i gnal output from t h e ampli fier at night i s a s sume d t o
be due t o sky wave and w i l l have b e e n amp l i f i e d by the
aerial sys t em by an am ount whi c h i s a func t i on of t h e angle
o f arri val . An ob vi ous , but u s e ful, ch e c k on t he s ys t e m
p e r f ormanc e i s t o ensure t hat t he output remai ns zero a l l
day and ret urns t o z e r o t he ne xt day f o l l owing t he flu c tua t i ons
at night .
3-3 : of the sky wave .
'i'hen , f o l l ow ing ad j us t i n g the sys t em as out lined
above , t he pr e s ent unit y gain pha s e lag !.1)1 i s i n t r oduc e d
int o the lead f r om aerial one , i t can e a s i ly b e sh own t hat
t ot a l cance l lat i on w i l l oc c ur from a si gnal arri ving at
b.rp = (