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G8MNY  > TECH     05.02.07 08:19l 59 Lines 2392 Bytes #999 (0) @ WW
BID : 1479_GB7CIP
Read: DL8FBH GUEST DL1GMC OE7FMI
Subj: Drake TC-3300-LP QRO LP Filter
Path: DB0FHN<DB0MRW<OK0PKL<OK0PCC<OM0PBC<OK0PPL<DB0RES<TU5EX<IW8PGT<VK4TRS<
      GB7YFS<GB7CIP
Sent: 070205/0029Z @:GB7CIP.#32.GBR.EU #:1479 [Caterham] $:1479_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To  : TECH@WW

By G8MNY                                         (Corrections Jan 07)
(8 Bit ASCII Graphics use code page 437 or 850)
I have reverse engineered this QRO HF Tx 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.

 0dB_³___________________
 -3dB´                   `\
-10dB´                     |
-20dB´                     |
-40dB´                      |
-60dB´                      |
-80dB´                       V~-._
     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.

      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 (      ===      (    C4===      ( ³   L2 = L6 = 0.4uH, 7 T on 15mm former.
 ³ ( L1    ³C2     ( L4    ³    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 though Mica washer disk.
C2 = C4 = 186pF bolted through double sided Mica washer disks.
C3 = 124pF larger bolted though Mica washer disk.

The 3 shunt traps L1/C1, L4/C3, & L7/C5 all resonate at 40MHz.

PHYSICAL CONSTRUCTION

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

The SO239s are riveted on, as are the 2 divider plates. The chassis has folded
edges not shown here for simplicity. The 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 base mounting. (eg. above is then upside down.)


Why Don't U send an interesting bul?

73 de John, G8MNY @ GB7CIP


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