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G8MNY > TECH 04.03.09 01:00l 63 Lines 2641 Bytes #999 (0) @ WW
BID : 19631_GB7CIP
Read: GUEST
Subj: Drake TC-3300-LP QRO LP Filter
Path: IZ3LSV<IK2XDE<F5GOV<F4BWT<VE2GPQ<VE3KPG<GB7CIP
Sent: 090303/2327Z @:GB7CIP.#32.GBR.EU #:19631 [Caterham] $:19631_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updates May 07)
(8 Bit ASCII Graphics use code page 437 or 850)
I have reverse engineered this high preformance QRO HF Tx low pass filter. It
was used with a QRO PA & it is nice to know, that no matter what QRM you may
cause other HF users, above HF all is quieter than can be measured!
The specification is 1kW MAX @ HF, Attenuation > 80dB above 41MHz.
Through loss is practically unmeasurable (< 0.05dB?).
0dB_³___________________
-3dB´ `\
-10dB´ |
-20dB´ |
-40dB´ |
-60dB´ |
-80dB´ V~Ä-._
ÅÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂ Freq
0 5 10 15 20 25 30 35 40 45 50 MHz
THE CIRCUIT
This is a type of M derived Low Pass filter with 3 suckout trap sections, as
well as « + 1 + « Pi low pass sections.
L2 L3 L5 L6 Coils are silver plated 3mm í wire.
o)ÄÂÄ(((()ÄÂÄ(((()ÄÂÄ(((()ÄÂÄ(((((ÄÂÄ(o L1 = L7 = 0.3uH, 8.5 T on 9mm former.
³ ( === ( === ( ³ L2 = L6 = 0.4uH, 7 T on 15mm former.
³ ( L1 ³C2 ( L4 ³C4 L7 ( ³ L4 = 0.13uH, 3.5 T on 9mm former.
³=== C1 ³ === C3 ³ C5 ===³ L3/5 = 0.4uH each, wound as centre
ÀÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÙ tapped of 15T on 15mm former.
C1 = C5 = 53pF bolted through Mica washer disk.
C2 = C4 = 186pF bolted through double sided Mica washer disks.
C3 = 124pF larger bolted through Mica washer disk.
The 3 shunt traps L1/C1, L4/C3, & L7/C5 all resonate at 40MHz.
PHYSICAL CONSTRUCTION
- - - - - - - - BOTTOM COVER REMOVED - - - - - - - -
SO239³ L2 ³ L3 L5 ³ L6 ³SO239
ÚÄÄ´ /~|||||| º³º /~||||||| ||||||| º³º ||||||~\ ÃÄÄ¿
³ ³] |||||| [º³º] ||||||| ||||||| [º³º] |||||| [³ ³
ÀÄÄ´ \ |||||_/ º³º ||||||||||||||_/ º³º \_||||| / ÃÄÄÙ
³ ððð ³C2 __/ C4³ ððð ³
³ ððð L1 ³ L4 ððð ³ L7 ððð ³
³ ___\n____C1 ³ ____\n____C3 ³ C5____n/___ ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
TOP CHASSIS
The SO239s are riveted on, as are the 2 divider plates. The top chassis has
folded edges tapped for screws etc. not shown here for simplicity. The bottom U
channel shaped cover is screwed on into the folded edges & it has RF fingering
to help ground the 2 central dividers. The cover is the bottom base mounting.
(e.g. above is upside down in use.)
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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