technical report, remediation, cable tv modulator and channel translator, report #05s

8/14/2019 Technical Report, Remediation, Cable TV Modulator and Channel translator, Report #05s

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Copyright 2009 _Jim

Any methods, techniques and depictions of same (including drawings, sketches,

pictures, images or graphical depictions)set forth in this document are property of the author/owner unless those rights areconferred or transferred to another company, individual or customer by theauthor/owner.

Any and all copyrights, trademarks, tradenames remain the property of their respective owners should reference to thosetrade-names or trademarks appear in thisdocument.

Author: [email protected]

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Interim Report:

Remediation of Spurious outputsOf Cable Head-End Converter

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Dwg Number - n/aDate - August 11, 2009Revised - August 18, 2009Related files - n/a

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-- Statement of Work --

Activity Objective (primary):

Reduction of spurious signal at the output of a 1U-sized rack-mounted cable head-endconverter unit

Spurious should be reduced to the level of 60 dBc or better (referred to Video carrier signallevel).

Activity Objective (secondary):

Recommend layout and/or component changes to achieve the above objective on production board. (See pg 8)

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-- Background --

The present layout stems from an earlier design using two separate shielded subassemblies.These separate subassemblies incorporated an Up converter and Down converter in physicallyseparate enclosures, with each converter embodying its respective VCO, RF mixer, amplifier andfilter circuitry.

The use of two separate shielded enclosures provided substantial isolation between signal processed in the Up and Down converters. Additionally, to keep crosstalk low between the twoenclosures includes special chassis-mounted feed-through capacitors were used on the DCsupply lines.

Above - Old on left and new unit on right

-250 kHz Responses:

Above Old on left (-49 dBc) and new unit initial response (-25 dBc) on right

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Unit #5 after changes (-62 dBc):

Amplifiers: ERA-3 (U22) and ERA-5 (U9) as amplifiers for Up Converter LO buffers withrespective Bias Resistors (Down Converter uses two ERA-3 amps)

Pad changes: From: To:R111 33 86 R118 10 56

Foil cuts: See attached/following pages

Added components: 1 Diddle: In Down Converter at mixer IF input4 caps: 3-on 12V DC, 1-in series with C130 (see pics following)1 Inductor: On 12V DC line (see pics following)

Before After ImprovementCH 58 Vid + 9.3 dBm (56.2 dBmV) + 11.8 dBm (58.7 dBmV) + 2.5 dBSpur 1 -19.3 dBc - 63 dBc 40 dBSpur 2 - 49.2 dBc - 66 dBc 16.8 dBSpur 3 * - - 49.7 dBc n/c

Notable spurs:CH58 427.25 MHz +11.8 dBm Measured at output of power ampSpur1 -0.250 MHz - 63 dBcSpur2 +-46 MHz - 66 dBcSpur3 * +-5 MHz - 49.7 dBc Due to 5 MHz Reference Oscillator

Note: * Spur 3 remediation not addressed in this report.

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Bottom: foil cuts

Arrow on left shows cut needed for 39 nH Inductor addition

Arrow on right shows cut in unused trace. Also note two solder blobs now cooneting unusedtrace to ground plane.

See next page for detail of added components

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Added components to 12V power

Cap 1 = 68 pF, 0603 size, SMEC capacitor

Cap 2, 3 = 470 pF, 0603 size, SMEC cap

Inductor = 39 nH

Be sure to cut foil under inductor before hand placing

Scrape away solder mask as required for caps andinductor

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Down Converter - Cuts and additions

- Upper left arrow: cut (just before via to bottom layer)

- Two right arrows: solder bridging (scrape away solder mask first)

- Lower arrow: added Diddle to input of PMC mixer

Note: Two 220 load resistors used for ERA-3 1 st and 2 nd buffer amplifiers respectively.

Advise:1) Ditch the extra layout for the alternative bandpass filters; make use of that extra real

estate to isolate bottom layer DC foil from over-running RF traces2) Pull solder mask back further to give the fence shields more ground plane to solder to3) Add pads for hand placement of 3-caps and 1-Inductor components on bottom of board to

isolate DC from Up and Down converters.4) Up-size/change pads for the required ERA-3 and 5 load resistors5) Provide easier mounting for mixer input Diddle; maybe mount it on bottom of board with

hole going to mixer input copper trace6) 5 MHz Spur: Probably need to re-route and LP filter 5 MHz from 5 MHz Ref Osc to

synthesizer to reduce this spur (untried at this juncture) and/or devise a LP filter to synth.

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Unit #5 test notes

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-- End --

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technical report, remediation, cable tv modulator and channel translator, report #05s

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