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G8MNY > TECHNI 22.12.25 18:44l 150 Lines 8008 Bytes #9 (0) @ WW
BID : 47679_GB7CIP
Subj: HF ATU & SWR Bridge VC300LP/QT-1
Path: JH4XSY<N3HYM<VE3CGR<PI8ZTM<CX2SA<OK2PEN<GB7CIP
Sent: 251222/0937Z @:GB7CIP.#32.GBR.EURO #:47679 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jan 19)
(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 they only have a 12
tap L switch & large lossy air inductor!
F R O N T R E A R
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾛﾛﾟﾟﾛﾛ ｳ ｳ 1 2 Rig ｳ
ｳ ｳ /~~~\ ｳ ﾛﾛﾛﾛﾛﾛ ﾛﾛﾜﾜﾛﾛ ﾛﾛﾛﾛﾛﾛ ｳ ｳ o (o) (o) (o) ｳ
ｳ ｳ|_/_\_|ｳ ﾛﾛ ﾛﾛ ﾜﾜﾜﾜﾜﾜ ﾛﾛ ﾛﾛ ｳ ｳ Bal ｳ
ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾙ ﾛﾛﾛﾛﾛﾛ ﾛﾛ ﾛﾛ ﾛﾛﾛﾛﾛﾛ ｳ ｳ Earth o o (o) * ｳ
ｳ o o o ﾟﾟﾟﾟﾟﾟ ｳ ｳ -o- Wire Byp 12vｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
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 ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
o)ﾄｴDUAL POWER &ﾃﾄｴ directﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴDUMMY LOADｳ
ｳ SWR METERS ｳ ｳAERIAL ｳ ｳAERIAL ﾃﾄ(o BYPASS ﾀﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
ﾀﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾙ ｳSELECT ｳ ｳSELECT ﾃﾄ(o COAX1 ﾁ ﾚﾄﾄﾄﾄﾄﾄﾄｿ
Lamp Range PEP ｳSWITCH ｳ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ｳSWITCH ﾃﾄ(o COAX2 >ﾄﾄｴ Balun ｳ
>ﾄﾄﾙ ｳ atuﾃﾄｴ A.T.U.ﾃﾄｴ ﾃﾄﾄ< WIRE >ﾄﾄｴ Trans ｳ
12V ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾂﾄﾄﾂﾄﾄﾂﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄｿ ﾀﾄﾄﾂﾄﾄﾄﾄﾙ
C L C _ｳ_Earth ﾁ
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, Max 10 seconds @ 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)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄ>oﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ﾄﾁﾄ ===== 50pｳ ==='Nul ｳ / oﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ(0 BYPASS
ﾚﾄﾄﾄCCCCCﾄﾄﾄｿ === 'ｳ2-20p ｳ Direct oﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ(0 COAX 2
ｳ ﾀﾄﾄﾄﾄﾄ)ﾄﾄﾅﾄﾄﾄｴ220p ｳ30p \ oﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾂﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ(0 COAX 1
ﾃﾄﾄﾄ111Rﾄﾄﾄﾄｴ L === === / oｿ ﾚﾄ>oﾙ ｳ ｳ ﾄﾁﾄ
_ｳ_ _ｳ_ ﾀﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄｴ Via oｴ ｳ oﾄﾄﾙ ｳ
\_/ 4x10n \_/Ge ﾄﾁﾄ ATU oｴ ｳ oﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ0 WIRE
ﾃﾄﾄｴﾃﾄﾂﾄｴﾃﾄﾄｴ \ oｴ ｳ oﾄﾄﾄﾄﾁﾂﾄﾄﾄｿ Dummy |
100R ｳ 100R ｳ_ ｳ_ 68p=== 50R Load | Bridge
ﾃﾄﾄｴﾃﾄﾅﾄｴﾃﾄﾄｴ +47u ｳ/ｳ ｳ/ｳ ﾀﾄﾄﾄｴ | For
ｳ ﾄﾁﾄ ﾃﾄﾄｴﾃﾄﾄｿ PEP Tx Cap === === Load ﾄﾁﾄ | Balanced
ﾚﾄﾁﾄﾂﾄﾄ100Kﾄｿ ﾃﾄ100Kﾄﾁﾄo\__ 35-200p/ｳ /ｳ Cap | Aerial
47K ﾃﾄﾄﾄｴﾃﾄﾄﾁﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄo\__ｳ ﾃﾄﾄﾄﾄﾄﾙ35-200p |
PRE ｳ +47u ﾚﾄﾁﾄｿ ﾄﾁﾄ A.T.U. ｳ ===== |
ｳ 47K 47K 47K ｳ ====== ﾚﾄCCCCCﾄ0 4:1
47K PRE PRE PRE AdjustableﾀﾄCCCCCC__ ｳ ﾄﾁﾄ BALUN
ﾀo oﾙ30w 60wﾀo oﾙ6w Ferrite /\____ｳ ﾀﾄﾄﾄﾄﾄﾄﾄ0 100R-1K
300\ \ Meter Inductor 0.2-40uH ﾄﾁﾄ
ﾃﾄｴﾃﾄﾂﾄﾄｴﾃﾄﾄｴ Switch ﾚﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄ0 EARTH
Forward ｳ Reverse ﾄﾁﾄ ｳ 10n===
Meter ｳ Meter ｳ ｳ
1K5ﾀﾄﾄﾄﾄﾁﾄﾂﾄﾄﾄﾄﾙ1K1 ﾀﾄMeterﾄﾁﾄﾄ(0 < 12V
200uA ﾄﾁﾄ 200uA Lamp ﾄﾁﾄ
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. But on
another model, it was 12 taps & switch on a large air spaced coil.
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
If doing this on someones operating frequency, DO QSY 3kHz first! 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 a 50R source & load the Cs
should end up being equal in value. After that, switch to the aerial & re-tweak
just the Cs for 1:1, they will no longer be equal on a non 50R load!
LOW POWER is the kindest tuning method for the ATU & also for minimum QRM. A
very briefly re-tweaking of Cs only at full power may be an advantage as the
meters are more sensitive to reflected SWR, 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) or add a series cap (200pF) or
L (20 turns 3cm dia) can help.
The "T" type ATU is easy to use, although it is not so good at removing Tx
harmonics as the � (pi) type. But it does an excellent job of protecting the Rx
from DC static, & strong signals on lower bands, that some poorly filtered SRD
Rx can suffer from! (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 "HF ATU & SWR Bridge MFJ-904H", "Palstar AT1500CV ATU"
"Drake WH7 QRO HF SWR Bridge", "A Homebrew HF SWR Bridge", "Testing Auto ATUs",
"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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