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G8MNY > TECH 23.10.24 08:24z 229 Lines 6848 Bytes #120 (0) @ WW
BID : 18427_GB7CIP
Read: GUEST
Subj: 12 Uses of HF Trifilair L
Path: SR1BSZ<EA2RCF<LU9DCE<K1AJD<VE3CGR<CX2SA<GB7CIP
Sent: 241023/0821Z @:GB7CIP.#32.GBR.EURO #:18427 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jun 20)
(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 50ohm 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 50ohm?). Test on the highest band again at
powers suitable for your 450ohm 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, works when there is an RF earth!)
Core handles only 25% of the total power!
Coax o)ÄÄCCCCCÄÄÄ
50ohm ³ '===== 35-70ohm 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.
Can give better or worse balance & Noise than 1/
Coax o)ÄÄÄ¿
³ ')||
50ohm ³ )||
³ ÃÄÄÄÄÄÄÄ
Unbalanced³ ')||
³ )|| 35-70ohm
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!
Can give better or worse balance & Noise than 1/ or /2 !
Coax o)ÄÄ¿ ÚÄÄÄ
50ohm ³ )||( 35-70ohm
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¿||( 150-300ohm
50ohm 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¿
50ohm ³ ')||
³ )||ÚÄÄÄ
³ ³||( 9-18ohm
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
50ohm ³ ')||
³ )|| 150-300ohm
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´|| 70-140ohm
50ohm 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¿
50ohm ³ ||('
³ ||(
³ ||ÃÄÄÄÄ
³ ||('
³ ||( 17-34ohm
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
')||
)|| 150-300ohm
Coax o)ÄÄ´||
50ohm 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¿
50ohm ³ ||('
³ ||(
³ ||ÃÄÄÄÄ
³ ||(' 9-18ohm
Unbalanced ³ ||( Unbalanced
ÃÄÄÄÄÁÄÄÄÄ
Á
11/ 1:3 Auto Transformer. 1:9 Z UnUn
Core handles 66% of the total power!
ÚÄÄÄÄÄÄ
')||
)||
³|| 320-640ohm
')||
)||
Coax o)ÄÄ´|| Unbalanced
50ohm ³ ')||
Unbalanced ³ )||
ÃÄÄÁÄÄÄÄÄÄ
Á
12/ 3:1 Auto Transformer. 9:1 Z UnUn
Core handles 66% of the total power!
Coax o)ÄÄÄÄ¿
50ohm ³ ||('
³ ||(
³ ||³
³ ||('
³ ||(
³ ||ÃÄÄÄÄ
Unbalanced ³ ||(' 4-8ohm
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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