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G8MNY > TECH 26.01.20 19:30l 233 Lines 7038 Bytes #999 (0) @ WW
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Subj: 12 Uses of HF Trifilair L
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From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Apr 15)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
A suitable RF ferrite ring or rod wound with 3 identical windings is quite
versatile, here we consider them for Tx Aerial use, but they are also used in
Detectors & Mixers.
The amount of ferrite in the core & material at a given frequency determines
the power handling. Core saturation shows up as SWR change at high power & core
heating after some time. The inductance is the square of the number of turns,
so increase it by 40% doubles the inductance! Maximum efficient is when the
core nearly saturates at full power at the lowest frequency. Both ferrite &
copper losses increase with frequency, but an unsaturated ferrite core coil has
much lower loss than an air cored one, due to the 10-100x less wire needed.
TURNS & WIRE LENGTH
To work well at low frequencies the inductance reactance must be much greater
than 50ê to the Tx, but to work well at high frequencies the total wire length
must be much less than a 1/4 wave! These 2 opposing parameters will limit the
number of bands a single choke can be used on!
To test your core is OK for all HF bands & powers, do the following tests..
ÚÄÄ¿ ÚÄÄÄ¿ ÚÄÄÄÄ¿ Use short connecting leads
³TxÃÄ´SWRÃÄÂÄ´LOAD³ to "T" in the inductor
ÀÄÄÙ ÀÄÄÄÙ L ÀÄÄÄÄÙ to a good dummy load.
Á
a) On low power, test how many turns are needed on the lowest band (1.8MHz) so
that the SWR is better than 1.3:1.
b) Now repeat that test at full power (400W), does the SWR change? Does the
core heat up? If it does either of these put on more turns, or double the
core size.
c) On low power, do the test on the highest band (30MHz), SWR should still be
good.
d) Now are 3 of these windings in series longer than 1/8 wavelength at the
highest frequency? If it is it will not work at that frequency! If shorter
then wire up as in 10/ below & terminate with good RF 450R e.g. 3x 150R
(used in // are they a good 50ê?). Test on the highest band again at powers
suitable for your 450R load. SWR still OK?
If your inductor passes these test, you have one suitable for all bands &
powers provided the aerial impedance is sensible!
HOUSING
Put the coil into a box with 2x SO239 & screw up wire terminals & earth post as
close to the 6 way connection terminal block. And leave the leads just long
enough to go to all options.
ÚÄÄÄÄÄÄÄÄ¿
³ /~~~~\ ³
³| /~~\ |³
SO239 ³| \__/ |ÿ SO239
RIG &Ú´ \____/ ÃÙ AERIALS
ATU À´[::::::]ÃÜ
Ü´/ ÇÙÀÙ \ÃÜ BALANCED & UNBALANCED
EARTH ÀÄÄÄÄÄÄÄÄÙ AERIAL TERMINALS
CONNECTIONS
Connect the 6 leads of the 3 windings to the 6 way connector block & wire up as
needed. (different colour wires/sleeves?)
THE 12 USES ARE...
(The ' indicates the start or one end of the windings)
1/ 1;1 Choke Balun. (uses 2 windings, work when there is an RF earth!)
Core handles only 25% of the total power!
Coax o)ÄÄCCCCCÄÄÄ
50ê ³ '===== 35-70ê Balanced
Unbalanced ÃÄÄCCCCCÄÄÄ (or unbalanced)
Á '
2/ 1:1 Transfomer Balun (works OK with high Z RF earths!)
Core handles only 50% of the power
Coax o)ÄÄÄ¿
³ ')||
50ê ³ )||
³ ÃÄÄÄÄÄÄÄ
Unbalanced³ ')||
³ )|| 35-70ê
ÃÄÄÄ´|| Balanced
Á ')||
)||
ÀÄÄÄÄÄÄÄ
3/ 1:1 Isolation Transformer. (uses 2 windings)
The inter-winding capacitance affects RF isolation.
Core handles 100% of the total power!
Coax o)ÄÄ¿ ÚÄÄÄ
50ê ³ )||( 35-70ê
Unbalanced ³ )||( Floating
ÃÄÄÙ ÀÄÄÄ
Á
4/ 1:2 Isolation Transformer. 1:4 Z
The inter-winding capacitance affects RF isolation.
Core handles 100% of the total power!
ÚÄÄÄ
||('
Coax o)ÄÄ¿||( 150-300ê
50ê ³ )||³
Unbalanced ³ )||(' Floating
ÃÄÄÙ||(
Á ÀÄÄÄ
5/ 2:1 Isolation Transformer. 4;1 Z
The inter-winding capacitance affects RF isolation.
Core handles 100% of the total power!
Coax o)ÄÄ¿
50ê ³ ')||
³ )||ÚÄÄÄ
³ ³||( 9-18ê
³ ')||( Floating
Unbalanced ³ )||ÀÄÄÄ
ÃÄÄÙ
Á
6/ 1:2 Balun Transformer. 1:4 Z (uses 2 windings)
Core handles 50% of the total power!
Coax o)ÄÄÂÄÄÄÄÄÄ
50ê ³ ')||
³ )|| 150-300ê
Unbalanced ÃÄÄ´||
Á ')|| Balanced
)||
ÀÄÄÄÄÄÄ
7/ 2:3 Auto Transformer. 1:2 Z UnUn
Core handles 33% of the total power!
ÚÄÄÄÄÄÄ
')||
)||
Coax o)ÄÄ´|| 70-140ê
50ê ³ ')||
³ )|| Unbalanced
³ ³||
Unbalanced ³ ')||
³ )||
ÃÄÄÁÄÄÄÄÄÄ
Á
8/ 3:2 Auto Transformer. 2:1 Z UnUn
Core handles 33% of the total power!
Coax o)ÄÄÄÄ¿
50ê ³ ||('
³ ||(
³ ||ÃÄÄÄÄ
³ ||('
³ ||( 17-34ê
³ ||³
Unbalanced ³ ||(' Unbalanced
³ ||(
ÃÄÄÄÄÁÄÄÄÄ
Á
9/ 1:2 Auto Transformer. 1:4 Z (uses 2 windings)
Core handles 50% of the total power!
ÚÄÄÄÄÄÄ
')||
)|| 150-300ê
Coax o)ÄÄ´||
50ê ³ ')|| Unbalanced
Unbalanced ³ )||
ÃÄÄÁÄÄÄÄÄÄ
Á
10/ 2:1 Auto Transformer. 4:1 Z UnUn (uses 2 windings)
Core handles 50% of the total power!
Coax o)ÄÄÄÄ¿
50ê ³ ||('
³ ||(
³ ||ÃÄÄÄÄ
³ ||(' 9-18ê
Unbalanced ³ ||( Unbalanced
ÃÄÄÄÄÁÄÄÄÄ
Á
11/ 1:3 Auto Transformer. 1:9 Z UnUn
Core handles 66% of the total power!
ÚÄÄÄÄÄÄ
')||
)||
³|| 320-640ê
')||
)||
Coax o)ÄÄ´|| Unbalanced
50ê ³ ')||
Unbalanced ³ )||
ÃÄÄÁÄÄÄÄÄÄ
Á
12/ 3:1 Auto Transformer. 9:1 Z UnUn
Core handles 66% of the total power!
Coax o)ÄÄÄÄ¿
50ê ³ ||('
³ ||(
³ ||³
³ ||('
³ ||(
³ ||ÃÄÄÄÄ
Unbalanced ³ ||(' 4-8ê
³ ||( Unbalanced
ÃÄÄÄÄÁÄÄÄÄ
Á
See my Tech Bul "Understanding Transformers".
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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