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G8MNY > TECH 10.01.05 19:31l 77 Lines 3477 Bytes #999 (0) @ WW
BID : 28251_GB7CIP
Read: DL8NCA GUEST
Subj: HF ATU & SWR Bridge VC300LP
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<IW8PGT<TU5EX<ON0BEL<GB7CIP
Sent: 050110/0940Z @:GB7CIP.#32.GBR.EU #:28251 [Caterham] $:28251_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Nov 04)
This is reverse engineered from an old VECTRONICS ATU Model VC300LP (Pre MFJ).
This small cheaply made unit has many advantages as there is a lot in one box.
FEATURES
4 Aerial Choices, Bypass, Coax 1, Coax 2, & Wire.
3 with ATU Option. (not Bypass but with dummy load if needed)
300W max. SSB ATU Rating.
ATU T Type, 50 tap Inductor, 2 tuning Caps.
Tuning & Power Meter Range 1.8-30MHz.
30 & 300W Forward scale cross needle power meter.
6 & 60W Reverse power scales.
Average & PEP meter modes.
Built in 100W dummy Load (5 min rated).
4:1 BALUN option for Wire aerials.
12V Meter scale Lamp.
CIRCUIT.
The SWR bridge is quite conventional. The PEP mode with large 47uF is not
effective an active system is really needed!
ring 50p 8 WAY O/P SELECT SWITCH
TX 0)ÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ>oÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
===== ³ ===' ³ / oÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄ(0 BYPASS
ÚÄÄCCCCCÄÄ¿ === '³2-20p ³ Direct oÄÄÄÄÄÄÄÄÄÂÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄ(0 COAX 2
³ ÀÄÄÄÄ)ÄÄÅÄÄÄ´ 30p³ \ oÄÄÄÄÄÄÄÄÄ)ÄÂÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄ(0 COAX 1
ÃÄÄ111RÄÄÄ´ L === === / o¿ ÚÄ>oÙ ³ ³
_³_ _³_ ÀÄÄÄÁÄÄÄÄÄÄ´ Via o´ ³ oÄÄÙ ³
\_/ 4x10n /_\Ge 220p ÄÁÄ ATU o´ ³ oÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄ0 WIRE
ÃÄ´ÃÄÂÄ´ÃÄ´ \ o´ ³ oÄÄÄÄÁÂÄÄÄ¿ Dummy |
100 ³ 100 ³ ³ 68p=== 50R Load | Bridge
ÃÄ´ÃÄÅÄ´ÃÄ´ +47u ³ ³ ÀÄÄÄ´ | For
³ ÄÁÄ ÃÄÄ´ÃÄÄ¿ PEP ³ ³ Load ÄÁÄ | Balanced
ÚÄÁÄÂÄ100K¿ ÃÄ100KÄÁÄo\__ Tx Cap ===' ==='Cap | Aerial
47K ÃÄÄ´ÃÄÁÄ)ÄÄÄÄÄÄÄÄo\__³ 200pF 'ÃÄÄÄÄÙ 200pF |
PRE ³ 47u ÚÄÁÄ¿ ÄÁÄ ³ A.T.U. ===== |
³ 47K 47K 47K ³ ====== ÚÄCCCCCÄ0 4:1
47K PRE PRE PRE Adjustable ÀÄCCCCCC_ ³ ÄÁÄ BALUN
Ào oÙ30w Ào oÙ6w Ferrite L /\____³ ÀÄÄÄÄÄÄÄ0
300\ 60w \ Meter ÄÁÄ
ÃÄ´ÃÂÄ´ÃÄÄ´ Switch ÚÄ0 EARTH
Forward³ Reverse ÄÁÄ
Meter ³ Meter
ÀÄÄÄÁÄÂÄÄÄÙ ÚÄÄLAMPÄÄÄ(0) < 12V
ÄÁÄ ÄÁÄ
CONSTRUCTION
Uses thick open were for all internal connections & the impedance is tamed by
the addition of extra caps to ground (eg the 68pF across the internal load &
30pF after the SWR Bridge). All earths are to the local chassis with lock
washers.
IN USE
The O/P select switch & the ATU variable L should not be operated with any
great power flowing as the contacts could be damaged.
The Ferrite Balun & ATU L can suffer saturation losses if inappropriately used,
but in general there is much less loss than the much bigger air spaced
equivalent unit as there is many times less copper loss. Typically the ATU only
losses 5% (0.2dB) of the power @ 100W.
The T type ATU is easy to use but is not very good at removing Tx harmonics,
but it does an excellent job of protecting the Rx from strong signals on lower
bands (eg. removing Broadcast signals).
The Meter needed damping as it is very swingy see my Meter damping/speedup bul
for corrective action.
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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