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G8MNY > TECH 03.08.14 09:32l 146 Lines 7693 Bytes #999 (0) @ WW
BID : 6829_GB7CIP
Read: GUEST
Subj: HF ATU & SWR Bridge VC300LP/QT-1
Path: IW8PGT<CX2SA<ZL2BAU<VK6HGR<GB7CIP
Sent: 140803/0739Z @:GB7CIP.#32.GBR.EURO #:6829 [Caterham Surrey GBR] $:6829_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Nov 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have reverse engineered this from an old VECTRONICS ATU Model VC300LP(PreMFJ)
which has a 48 turn sliding contact high Q ferrite L. But it looks the same as
the VC-300DPL, & also the Canadian AEA's QT-1 model but that one has only a
simple 12 tap switched large lossy air inductor.
F R O N T R E A R
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ ÚÄÄÄÄÄÄÄ¿ ÛÛßßÛÛ ³ ³ 1 2 Rig ³
³ ³ /~~~\ ³ ÛÛÛÛÛÛ ÛÛÜÜÛÛ ÛÛÛÛÛÛ ³ ³ o (o) (o) (o) ³
³ ³|_/_\_|³ ÛÛ ÛÛ ÜÜÜÜÜÜ ÛÛ ÛÛ ³ ³ Bal ³
³ ÀÄÄÄÄÄÄÄÙ ÛÛÛÛÛÛ ÛÛ ÛÛ ÛÛÛÛÛÛ ³ ³ Earth o o (o) * ³
³ o o o ßßßßßß ³ ³ -o- Wire Byp 12v³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
It is a small cheaply made unit, but it does have many advantages as there is a
lot in the one box.
Aerial Tuning Units are also called Aerial Matching Units, but the best aerial
is one that is already tuned by design (cutting) & a good match (tap point)!
BLOCK DIAGRAM
Rig ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄ¿
o)Ä´ POWER & ÃÄ´ directÃÄÄÄÄÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´DUMMY LOAD³
³ SWR METERS ³ ³ AERIAL ³ ³ AERIAL ÃÄ(o BYPASS ÀÄÄÄÄÄÄÄÄÄÄÙ
ÀÂÄÄÄÄÄÄÂÄÄÄÄÄÂÙ ³ SELECT ³ ³ SELECT ÃÄ(o COAX1 ÚÄÄÄÄÄÄÄ¿
Lamp Range PEP ³ SWITCH ³ ÚÄÄÄÄÄÄÄ¿ ³ SWITCH ÃÄ(o COAX2 >Ä´ Balun ³
>ÄÄÙ ³ atuÃÄ´ A.T.U.ÃÄ´ ÃÄÄ< WIRE >Ä´ Trans ³
12V ÀÄÄÄÄÄÄÄÄÄÙ ÀÂÄÄÂÄÄÂÙ ÀÄÄÄÄÄÄÄÄÁÄ¿ ÀÄÄÄÄÄÄÄÙ
C L C _³_Earth
FEATURES
8 Position Switch:- 4 Aerial Choices, Bypass, Coax 1, Coax 2, & Wire.
4 Option with ATU:- 3 Aerials & 1 Dummy load for pre tuning.
300W max. (150W @ 1.8MHz) SSB ATU Rating. 4:1 Max SWR @ 300W.
ATU is "T" Type, 48 tapped ferrite inductor, 2 tuning Caps (1000V rating).
30W & 300W Forward scale cross needle power meter.
6W & 60W Reverse power scales, for increased SWR sensitivity.
Average & PEP meter modes. (PEP poor design)
Built in dummy Load (50W cont, 10 seconds 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 for true PEP!
Ferrite ring 8 WAY SELECTOR SWITCH
TX 0)ÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ>oÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
ÄÁÄ ===== 50p³ ==='\ ³ / oÄÄÄÄÄÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄ(0 BYPASS
ÚÄÄÄCCCCCÄÄÄ¿ === '³2-20p ³ Direct oÄÄÄÄÄÄÄÄÄÄÂÄÄÄ)ÄÄÄÄÄÄÄÄÄÄÄÄ(0 COAX 2
³ ÀÄÄÄÄÄ)ÄÄÅÄÄÄ´220p ³30p \ oÄÄÄÄÄÄÄÄÄÄ)ÄÂÄ)ÄÄÄÄÄÄÄÄÄÄÄÄ(0 COAX 1
ÃÄÄÄ111êÄÄÄÄ´ L === === / o¿ ÚÄ>oÙ ³ ³ ÄÁÄ
_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=== 50ê Load | Bridge
ÃÄÄ´ÃÄÅÄ´ÃÄÄ´ +47u ³/| |\³ ÀÄÄÄ´ | For
³ ÄÁÄ ÃÄÄ´ÃÄÄ¿ PEP Tx Cap === === Load ÄÁÄ | Balanced
ÚÄÁÄÂÄÄ100kÄ¿ ÃÄ100kÄÁÄo\__ 35-200p/³ ³\ Cap | Aerial
47k ÃÄÄÄ´ÃÄÄÁÄ)ÄÄÄÄÄÄÄÄo\__³ ÃÄÄÄÄÄÙ 35-200p |
PRE ³ +47u ÚÄÁÄ¿ ÄÁÄ ³ A.T.U. ===== |
³ 47k 47k 47k ³ ====== ÚÄCCCCCÄ0 4:1
47k PRE PRE PRE AdjustableÀÄCCCCCC__ ³ ÄÁÄ BALUN
Ào oÙ30w 60wÀo oÙ6w Ferrite /\____³ ÀÄÄÄÄÄÄÄ0 100ê-1kê
300\ \ Meter Inductor 0.2-40uH ÄÁÄ
ÃÄ´ÃÄÂÄÄ´ÃÄÄ´ Switch ÚÄÄÂÄÄÄÄÄÄÄÂÄÄ0 EARTH
Forward ³ Reverse ÄÁÄ ³ 10n===
Meter ³ Meter ³ ³
1k5ÀÄÄÄÄÁÄÂÄÄÄÄÙ 1k1 ÀÄMeterÄÁÄÄ(0 < 12V
200uA ÄÁÄ 200uA Lamp ÄÁÄ
CONSTRUCTION
It uses thick 2 U part aluminium case, thick open wire for all internal
connections & the impedance is then tamed by the addition of extra caps to
ground. (e.g. 68pF across the internal load & 30pF after the SWR Bridge.)
The toroid ferrite inductor has a sliding contact over 48 separated turns on a
moulded former, some similar models just have 12 taps to a switch.
A single PCB provides for all the component mounting except the main switch,
ATU components, & dummy load. All earths are to the local chassis with locking
washers.
The SWR bridge circuit has a few added components to ensure accuracy over the
whole HF frequency range.
TUNING UP
The best tuning method is to use the ATU into the dummy load first at low power
(between 10 & 30W) & pre-tune it, set the ATU with both Cs @ 50% & adjust the L
tap for initial minimum SWR. Then tweak (rock too & throw) both the Cs for a
perfect 1:1 match. This can take time as they are interdependant & their
combined capacitance tunes the L for the frequency used & on 50ê source & load
Cs will be equal in value. After that, switch to the aerial & re-tweak the Cs
for 1:1, they will no longer be equal on a non 50ê load!
This is kindest tuning method for the ATU & also for minimum QRM to others. A
very briefly re-tweaking of Cs only at full power may be an advantage as the
meters are more accurately (sensitive) with more power.
Both the output select switch & the ATU variable L, should not be changed if
there is any great power flowing, as the contacts could be damaged with arcing!
IN USE
The ferrite balun & tapped ATU inductor can suffer saturation losses if used
in-appropriately. But in general there is much less loss with a ferrite cored
device, than the much bigger air spaced equivalents, as there is many times
less wire needed & associated copper loss. Typically power loss is only 5%
(0.2dB) @ 100W (100W in 95W out) on any band at any SWR (due to the "T" type
ATU's high Q) which is quite low for a combined ATU & SWR bridge.
If the random wire aerial won't tune up to give 1:1 SWR then try a different
length wire (shorter or longer by a metre or so).
The "T" type ATU is easy to use, but is not so good at removing Tx harmonics as
the ã (pi) type. But it does an excellent job of protecting the Rx from strong
signals on lower bands (e.g. removing MW Broadcast signals as it is >-18dB for
each frequency halving.)
MODS
1/ The black knobs on black background are not that visible, I have painted
white lines on mine, so I can easily see their directions in low light.
2/ I blackened the dummy load & the aluminium plate it is on, with spray mat
black, & used heat compound between that & box bottom. This all improves the
load's dissipation, so more power for longer is possable, or less chance or
burning it out!
3/ The cross needle meter needed damping as it is, is very swingy, see my Meter
damping/speed up bulletin for corrective action.
See also my Tech buls on "Palstar AT1500CV ATU", "Drake WH7 QRO HF SWR Bridge",
"A Homebrew HF SWR Bridge", "PEP Meter modification", "Meter Damping & Speed
Up" & "QRP SWR Bridge".
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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