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G8MNY > TECH 08.09.05 18:49l 80 Lines 4039 Bytes #999 (0) @ WW
BID : 61310_GB7CIP
Read: GUEST DL1LCA OE7FMI
Subj: HF ATU & SWR Bridge VC300LP
Path: DB0FHN<DB0THA<DB0HDF<DB0HOT<DB0MRW<OK0PKL<OK0PPL<DB0RES<ON0AR<ZL2BAU<
VK6HGR<GB7YFS<GB7WSX<GB7CIP
Sent: 050908/1157Z @:GB7CIP.#32.GBR.EU #:61310 [Caterham] $:61310_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Mar 05)
I have reverse engineered this from an old VECTRONICS ATU Model VC300LP(PreMFJ)
which seems the same as the VC-300DPL model. It is a small cheaply made unit,
but it does have many advantages as there is a lot in the one box.
FEATURES
8 Position Switch offers.. 4 Aerial Choices, Bypass, Coax 1, Coax 2,
& Wire. 3 have ATU Option. (not Bypass but with dummy load if needed)
300W max. (150W @ 1.8MHz) SSB ATU Rating. 4:1 Max SWR @ 300W.
ATU is "T" Type, 48 tap Inductor, 2 tuning Caps (1000V rating).
30 & 300W Forward scale cross needle power meter.
6 & 60W Reverse power scales, for increased SWR senitivity.
Average & PEP meter modes. (pep poor design)
Built in dummy Load (50W cont, 1 Min rated @ 300W ?).
4:1 BALUN option for balanced aerials (link from wire ant)
12V Meter scale Lamp & on/off switch.
Size 10.2 x 9.4 x 3.5" or 257 x 85 x 197mm, weight 3.4LBs
CIRCUIT.
The SWR bridge is quite conventional. The PEP mode with large 47uF is not
effective an active system is really needed!
ring 8 WAY O/P SELECT SWITCH
TX 0)ÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ>oÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
_³_ ===== 50p³ ==='\ ³ / oÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄ(0 BYPASS
ÚÄÄÄCCCCCÄÄÄ¿ === '³2-20p ³ Direct oÄÄÄÄÄÄÄÄÄÂÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄ(0 COAX 2
³ ÀÄÄÄÄÄ)ÄÄÅÄÄÄ´220p ³30p \ oÄÄÄÄÄÄÄÄÄ)ÄÂÄ)ÄÄÄÄÄÄÄÄÄÄÄÄ(0 COAX 1
ÃÄÄÄ111RÄÄÄÄ´ L === === / o¿ ÚÄ>oÙ ³ ³ _³_
_³_ _³_ ÀÄÄÄÁÄÄÄÄÄÄ´ Via o´ ³ oÄÄÙ ³
\_/ 4x10n /_\Ge ÄÁÄ ATU o´ ³ oÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÄ0 WIRE
ÃÄÄ´ÃÄÂÄ´ÃÄÄ´ \ o´ ³ oÄÄÄÄÁÂÄÄÄ¿ Dummy |
100 ³ 100 ³ ³ 68p=== 50R Load | Bridge
ÃÄÄ´ÃÄÅÄ´ÃÄÄ´ +47u ³ ³ ÀÄÄÄ´ | For
³ ÄÁÄ ÃÄÄ´ÃÄÄ¿ PEP ³ ³ Load ÄÁÄ | Balanced
ÚÄÁÄÂÄÄ100KÄ¿ ÃÄ100KÄÁÄo\__ Tx Cap ===' ==='Cap | Aerial
47K ÃÄÄÄ´ÃÄÄÁÄ)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´ÃÄÂÄÄ´ÃÄÄ´ Switch ÚÄ0 EARTH
Forward ³ Reverse ÄÁÄ
Meter ³ Meter Meter
ÀÄÄÄÄÁÄÂÄÄÄÄÙ ÚÄÄLampÄÄÄ(0 < 12V
ÄÁÄ ÄÁÄ _³_
CONSTRUCTION
Uses thick 2 part aluminium case, 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). 1 PCB provides all the
compoment except the main switch, ATU components, & dummy load. 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 wire & associates copper
loss. Typically the ATU only losses 5% (0.2dB) of the power @ 100W on any band
at any SWR.
The "T" type ATU is easy to use but is not so 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 cross needle 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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