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G8MNY  > TECH     11.05.19 11:00l 73 Lines 2923 Bytes #1 (0) @ WW
BID : 4032_GB7CIP
Read: GUEST
Subj: Drake TC-3300-LP QRO LP Filter
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 190511/0849Z @:GB7CIP.#32.GBR.EURO #:4032 [Caterham Surrey GBR] $:4032_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                     (Update Oct 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

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!

It has other uses, where say 3el HF tribander with 400W is below a 6M 5el beam
feeding a band filtered Rig enabling reduced QRM between both bands.

The specification is 1kW MAX @ HF, Attenuation > 80dB above 41MHz
Through loss is practically unmeasurable (< 0.05dB?) DC-30MHz

 0dB___________________
 -3dB                  ~\
-10dB                    
-20dB                    |
-30dB                    
-40dB                     
-50dB                     |
-60dB                     
-70dB                      |
-80dB                       V~-._
      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  wire
o)(((()(((()(((()((((((o  L1 = L7 = 0.3uH, 8.5 T on 9mm former
  (      ===      (      ===      (    L2 = L6 = 0.4uH, 7 T on 15mm former
  ( L1    C2     ( L4    C4  L7 (    L4 = 0.13uH, 3.5 T on 9mm former
 === C1         === C3      C5 ===   L3/5 = 0.4uH each, wound as centre
           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 - - - - - - - -
SO239    L2             L3       L5           L6      SO239
  Ĵ /~||||||    /~||||||| |||||||      ||||||~\ Ŀ
    ]  ||||||  []  ||||||| |||||||  []  ||||||  [  
  Ĵ \  |||||_/     ||||||||||||||_/  \_|||||  / 
               C2       __/         C4          
        L1           L4                 L7   
      ___\n___C1       _____\n_____C3      C5___n/___ 
     
                         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.)


See my tech bul "6m VHF Filter Design"


Why Don't U send an interesting bul?

73 de John, G8MNY @ GB7CIP


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