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G8MNY > TECH 26.09.10 00:34l 140 Lines 7248 Bytes #999 (0) @ WW
BID : 62696_GB7CIP
Read: DD3IA GUEST DG4IAK
Subj: HF ATU & SWR Bridge VC300LP/QT-1
Path: DB0FHN<DB0FOR<DF0ANN<DB0MRW<DB0ERF<DB0FBB<DB0IUZ<DB0GOS<ON0AR<IW8PGT<
IR2UBX<IK2XDE<DB0RES<DK0WUE<7M3TJZ<ZL2BAU<ON0BEL<GB7CIP
Sent: 100925/2226Z @:GB7CIP.#32.GBR.EU #:62696 [Caterham] $:62696_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Jun 09)
(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 seems the same as the VC-300DPL, & also the Canadian AEA's QT-1 model but
that one has only a simple 12 tap switched inductor.
F R O N T R E A R
ZDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD? ZDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD?
3 ZDDDDDDD? [[__[[ 3 3 1 2 Rig 3
3 3 /~~~\ 3 [[[[[[ [[\\[[ [[[[[[ 3 3 o (o) (o) (o) 3
3 3|_/_\_|3 [[ [[ \\\\\\ [[ [[ 3 3 Bal 3
3 @DDDDDDDY [[[[[[ [[ [[ [[[[[[ 3 3 Earth o o (o) * 3
3 o o o ______ 3 3 -o- Wire Byp 12v3
@DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDY @DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDY
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 ZDDDDDDDDDDDDDD? ZDDDDDDDDD? ZDDDDDDDD? ZDDDDDDDDDD?
o)D4 POWER & CD4 directCDDDDDDDDDDD4 CDDDDDDDDDDDDDD4DUMMY LOAD3
3 SWR METERS 3 3 AERIAL 3 3 AERIAL CD(o BYPASS @DDDDDDDDDDY
@BDDDDDDBDDDDDBY 3 SELECT 3 3 SELECT CD(o COAX1 ZDDDDDDD?
Lamp Range PEP 3 SWITCH 3 ZDDDDDDD? 3 SWITCH CD(o COAX2 >D4 Balun 3
>DDY 3 atuCD4 A.T.U.CD4 CDD< WIRE >D4 Trans 3
12V @DDDDDDDDDY @BDDBDDBY @DDDDDDDDAD? @DDDDDDDY
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 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)DDDDDDDDDDDDDBDDDBDDDDDDBDDDDDDDDD>oDDDDDDDDDDDDDD?
DAD ===== 50p3 ==='\ 3 / oDDDDDDDDDDDDDD)DDDDDDDDDDDD(0 BYPASS
ZDDDCCCCCDDD? === '32-20p 3 Direct oDDDDDDDDDDBDDD)DDDDDDDDDDDD(0 COAX 2
3 @DDDDD)DDEDDD4220p 330p \ oDDDDDDDDDD)DBD)DDDDDDDDDDDD(0 COAX 1
CDDD111jDDDD4 L === === / o? ZD>oY 3 3 DAD
_3_ _3_ @DDDADDDDDD4 Via o4 3 oDDY 3
\_/ 4x10n \_/Ge DAD ATU o4 3 oDDDD)DDDDDDDDDDDDD0 WIRE
CDD4CDBD4CDD4 \ o4 3 oDDDDABDDD? Dummy |
100 3 100 3_ _3 68p=== 50j Load | Bridge
CDD4CDED4CDD4 +47u 3/| |\3 @DDD4 | For
3 DAD CDD4CDD? PEP Tx Cap === === Load DAD | Balanced
ZDADBDD100kD? CD100kDADo\__ 35-200p/3 3\ Cap | Aerial
47k CDDD4CDDAD)DDDDDDDDo\__3 CDDDDDY 35-200p |
PRE 3 +47u ZDAD? DAD 3 A.T.U. ===== |
3 47k 47k 47k 3 ====== ZDCCCCCD0 4:1
47k PRE PRE PRE Adjustable @DCCCCCC_ 3 DAD BALUN
@o oY30w @o oY6w Ferrite /\____3 @DDDDDDD0 100j-1kj
300\ 60w \ Meter Inductor 0.2-40uH DAD
CD4CDBDD4CDD4 Switch ZDDBDDDDDDDBDD0 EARTH
Forward 3 Reverse DAD 3 10n===
Meter 3 Meter 3 3
1k5@DDDDADBDDDDY 1k1 @DMeterDADD(0 < 12V
200uA DAD 200uA Lamp DAD
CONSTRUCTION
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 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 about 50% & adjust
the L tap for initial minimum SWR, then tweak (rock too & throw) both Cs for a
perfect 1:1 match. Then switch to the aerial & re-tweak the Cs for 1:1.
This is kindest for the ATU & also for minimum QRM to others. Very briefly
re-tweaking at full power may be an advantage as the meters are more accurately
(sensitive) with more power.
Both the outputs 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 & 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 & associates copper loss. Typically loss is only 5% (0.2dB) of
the power @ 100W (100 in 95 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 the try a different
length (shorter by a metre or so).
The "T" type ATU is easy to use, but is not so good at removing Tx harmonics as
the c (pi) type. But it does an excellent job of protecting the Rx from strong
signals on lower bands (e.g. removing Broadcast signals as it is >-18dB for
each frequency halving.)
MODS
1/ The black knobs on black background are not 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, to improve the load
dissipation.
3/ The cross needle meter needed damping as it 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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