Understanding Un-Modules

Understanding Un-Modules

Understanding Un-Modules

Understanding Un-Modules


Un-mod­ules are sim­ple de­vices that plug in­to the K2 in place of some options They are use­ful be­cause the K2’s cir­cuit paths have to be modified be­fore in­stall­ing most op­tions, and in most cas­es once these mod­i­fi­ca­tions have been made, the ra­dio will not op­er­ate if the op­tions are ab­sent.  This is where the cus­tom circuits on un-mod­ule op­tion by­pass head­ers come in­to play.  They quick­ly un­do these cir­cuit path mod­i­fi­ca­tions, en­a­bling the ra­dio to func­tion when an op­tion is ab­sent.

A Formal Definition

un-   prefix

To reverse or undo a specific action.

mod·ule   noun

A self-con­tained as­sem­bly of elec­tron­ic com­po­nents and cir­cuit­ry that is in­stalled as a unit.


[The term un-mod­ule was coined by Mark Dul­cey (KE1L) in his Au­gust 2001 ar­ti­cle “Mak­ing Un-Mod­ules: Re­mov­ing Mod­ules with­out Re­work”, which de­scribes by­pass head­ers for most K2 op­tions avail­a­ble at the time.]

Un-mod­ules en­a­ble the K2 to op­er­ate af­ter their as­so­ci­at­ed options have been re­moved.  Their cir­cuit­ry re­stores the af­fect­ed cir­cuit paths back to their “orig­i­nal” con­fig­u­ra­tion, as they were pri­or to hav­ing been mod­i­fied in prep­a­ra­tion for the op­tion’s in­stal­la­tion.  Un-mod­ules al­so sim­pli­fy in­stal­la­tion of the nec­es­sary by­pass de­vices so that they can be in­stalled with­out re­fer­ring to the K2 sche­mat­ics.


Be­sides their in­te­gral role in our re­work-free “Op­tion Ready” K2 as­sem­bly method, there are many oth­er sit­u­ations where un-mod­ules might come in handy …

  1. If your K2 no long­er works af­ter you mod­i­fy it for and in­stall a new op­tion, you can quick­ly iso­late the fault down to ei­ther the op­tion or your K2.
  2. If you want to mod­i­fy an op­tion, you can con­tin­ue to use your ra­dio in its ab­sence.
  3. While mod­i­fy­ing your ful­ly load­ed K2, you might find it help­ful or even nec­es­sary to re­move some options (Such as re­mov­ing the KSB2 when chang­ing the val­ue of RF-R98 per the “Pow­er Con­trol” app note / “ALC Mod­u­la­tion” fix.)
  4. They per­mit sig­nal trac­ing most of the por­tions of the K2’s cir­cuit boards that are oth­er­wise hid­den un­der the op­tions.  (Sim­i­lar­ly, if you have the KDSP2 in­stalled and you want to re­do the 4 MHz os­cil­la­tor cal­i­bra­tion, you can re­move it to ac­cess test-point 3 on the RF board.)
  5. If you want to com­pare per­for­mance both with and with­out an op­tion in­stalled.  (Just be sure to pow­er off your K2 while do­ing the swap­ping.)
  6. Un-mod­ules fa­cil­i­tate ra­pid board-lev­el fault iso­la­tion, in the event that your ful­ly-load­ed K2 stops work­ing al­to­geth­er.
2001 KE1L
Mark's homebrew devices.
2005 WB2ART
Ken's UNPCBs
Original rev D
2006 KI4GGX
2nd generation rev G
A Brief Chronology

AUG ’01 – KE1L’s Original Article

APR ’04 – KI4GGX’s Correction
Ad­vi­so­ry that an UN-KNB2 re­sis­tor val­ue was in­cor­rect.

APR ’05 – WB2ART’s Prototypes

MAY .. AUG ’05 – rev D kit

JUL .. AUG ’06 – rev G kit
Re­leased 2nd generation PCB in re­sponse to us­er feed­back:

  • Add­ed UN-KNB2 mount­ing hole (LU5OM).
  • Add­ed dual ground planes (N8LP).
Circuit Diagram/Description

Two op­tion-sup­plied con­nect­ors must be add­ed to the RF board to sup­port all of the options – KAT2, KBT2, KIO2, KPA100 – that mount in the top cov­er of the K2 en­clo­sure.  In con­trast, pri­or to in­stall­ing the six op­tions – KNB2, KSB2, K60XV, K160RX, KAF2, KDSP2 – that plug di­rect­ly on­to the K2’s main cir­cuit boards, 13 “orig­i­nal” parts must be re­moved and 25 “new” op­tion-sup­plied parts must be in­stalled.  Once the ra­dio has been mod­i­fied to ac­cept any of these six plug-in op­tions, it will not func­tion un­less that op­tion is in­stalled.

Un-mod­ule op­tion by­pass head­ers pro­vide an easy rem­e­dy to this sit­u­ation.  They ef­fec­tive­ly re­store the ra­dio back to its “stock” elec­tri­cal con­fig­u­ra­tion, so it will func­tion if an op­tion is ab­sent.  This is il­lus­trat­ed in the col­or-cod­ed diagram be­low, which de­picts the por­tions of the K2 sche­mat­ics that re­late to un-mod­ules.  The di­a­gram al­so shows the “ex­ter­nal” res­to­ra­tion cir­cuit­ry on the head­ers them­selves.

Hybrid un-module circuit/block diagram thumbnail
The K2 schematics are the intellectual property of Elecraft, Inc. Copyright © 1999 – 2013, all rights reserved, used with permission.

Twelve “un-mod­ule re­lat­ed” parts must be re­moved from the K2 while pre­par­ing to ful­ly load it with op­tions.  These parts in­clude:  two caps C6 & C167; three re­sis­tors R88, R89, & R90; and sev­en op­tion by­pass jump­ers (A.K.A. ze­ro-ohm re­sis­tors) W1, W2, W3, W5, W6, R18, & R19

Eight of these re­moved parts must be re­placed, and it is worth not­ing that in five cas­es the re­place­ment parts are Sin­gle In­line Pack­age (SIP) mat­ing con­nect­ors – RF-J9, RF-J10, RF-J15, CTRL-J1, & CTRL-J2 – on which the op­tions will be in­stalled.  The de­tails of these eight remove-and-replace (PCB rework) chang­es are as fol­lows:

  • The orig­i­nal 470 Ω R88 is re­moved from the RF board, and re­placed by a 2.7 kΩ R88 which is sup­plied with the KNB2 op­tion.
  • R89 is re­moved from the RF board, and re­placed by a jump­er wire (A.K.A. W89).
  • Jump­er wires W2 & W3 on the RF board are re­moved and re­placed with KSB2 sup­plied SIP mat­ing con­nect­ors J9 & J10 (Crys­tal Fil­ter In & Crys­tal Fil­ter out).
  • Ze­ro Ohm re­sis­tors (i.e. jump­er wires) R18 & R19 are re­moved from the bot­tom of the Con­trol board, to clear the way for the in­stal­la­tion of KAF2 & KDSP2 sup­plied SIP mat­ing con­nect­ors J1 & J2 (Au­dio Fil­ter In & Au­dio Fil­ter Out) on the top of the board.
  • C6 is re­moved from the bot­tom of the RF board and re­placed with K60XV sup­plied SIP mat­ing con­nect­or J15 (60 Me­ters), which is in­stalled on the top of the board.
  • Not shown in the di­a­gram … the orig­i­nal 82 pF C71 is re­moved from the RF board, and re­placed by a 120 pF C71 which is sup­plied with the K60XV op­tion.

Re­plac­ing com­po­nents (and jump­er wires) with mat­ing con­nect­ors for the options re­quires the ut­most care when re­mov­ing the orig­i­nal parts.  Oth­er­wise, the SIP con­nect­ors might not sit per­fect­ly flush and square on the re­worked cir­cuit board.  Even if they do, the re­sult­ing in­stal­la­tion still might not re­main me­chan­i­cal­ly sound and func­tion re­li­a­bly for the life of the ra­dio.  Con­cern about the re­li­a­bil­i­ty im­pact of this PCB re­work was our mo­ti­va­tion for de­vel­op­ing the al­ter­nate K2 as­sem­bly method de­scribed in our Re­work Elim­i­na­tors™ Companion Guides.  Our meth­od yields an “Op­tion Ready” K2, which can be ful­ly pop­u­lat­ed with op­tions with­out re­quir­ing PCB re­work.  (Un-mod­ules play a cru­cial role in mak­ing this pos­si­ble.)

Ful­ly load­ing a K2 with op­tions re­quires the in­stal­la­tion of many more “op­tion sup­plied” parts be­yond those shown in the above di­a­gram.  These “oth­er” parts aren’t men­tioned be­cause they don’t re­quire “un-do­ing” for the K2 to op­er­ate af­ter their as­so­ci­at­ed op­tions are re­moved.  In­ter­est­ed read­ers will find all 40 “op­tion prep­a­ra­tion” chang­es (two+13+25=40) on the an­no­tat­ed K2 sche­mat­ics in Ap­pen­dix B of our companion guides.

Original KE1L Homebrew Article

[Ele­craft] K2 Un-Mod­ules

from [Mark J. Dulcy]

Subject:[Elecraft] K2 Un-Modules
From:"Mark J. Dulcey" <mark@•••••••.org>
Date:Wed, 15 Aug 2001 17:29:42 -0400

I wrote an article about some little things I built recently...  I'm thinking this could become a Tech Note at Elecraft, but I'd like comments first.

Making Un-Modules: Removing Modules without Rework
Mark J. Dulcey, KE1L
Edited by KI4GGX
(Reproduced with Permission)

The KSB2, KNB2, and K160RX op­tions add de­sir­a­ble fea­tures to the K2.  How­ev­er, once they’ve been in­stalled there’s no easy way to tem­po­rar­i­ly re­move them.  Pri­or to their in­stal­la­tion, one or more by­pass jump­er wires must be re­moved from the RF board.  In ad­di­tion, for some op­tions a few oth­er com­po­nents must al­so be re­moved or re­placed.  Be­cause of these chang­es, you can’t just un­plug these op­tions be­cause the ra­dio won’t op­er­ate with­out them.

Un­til now, the com­mon­ly ac­cept­ed meth­od of re­mov­ing an op­tion has been to un­do the chang­es that were made to the RF board when the op­tion was first in­stalled.  That might be an ac­cept­a­ble so­lu­tion if you are per­ma­nent­ly re­mov­ing it, but what if you only want to take one out tem­po­rar­i­ly for any of the fol­low­ing rea­sons?

  • To mod­i­fy it
  • For high-lev­el fault iso­la­tion (in case the ra­dio stops work­ing al­to­geth­er)
  • For sig­nal trac­ing parts of the RF board that are oth­er­wise hid­den
homebrew un-modules

Enter the Un-Modules!  By us­ing these sim­ple and easy-to-build de­vices, you can quick­ly re­move their as­so­ci­at­ed op­tions with­out mod­i­fy­ing your K2!  You’ll note that un-mod­ules aren’t ex­act­ly the same as re­mov­ing an op­tion by the tra­di­tion­al K2 PCB re­work meth­od, since the re­sult­ing sig­nal paths will be a lit­tle long­er.  Thus, sig­nal leak­age and stray in­duc­tance and/or ca­pac­i­tance may be slight­ly high­er.  Even so, with prop­er con­struc­tion prac­tic­es they still ought to be bet­ter than with the ac­tu­al op­tions in­stalled, so the im­pact of un-mod­ules is prob­a­bly neg­li­gi­ble.  More im­por­tant­ly, by us­ing un-mod­ules you’ll be spar­ing your RF board from re­peat­ed PCB re­work and the very real pos­si­bil­i­ty of se­ri­ous dam­age as a re­sult!  In sum­ma­ry, the ben­e­fits of un-mod­ules … 1) they make it re­al­ly easy to re­move the op­tions and 2) they elim­i­nate the chance of dam­ag­ing your K2 … should out­weigh any con­cerns about their pos­si­ble neg­li­gi­ble im­pact on per­for­mance.

What you’ll need.  Fore­most, you need the prop­er Sin­gle In­line Pack­age (SIP) ter­mi­nal strip con­nect­ors.  They must have gold-plat­ed mat­ing con­tacts, where­as tin plat­ing is ac­tu­al­ly pref­er­a­ble for the sol­der-tails.  The mat­ing con­tacts (posts) should be at least 230 mils (.230") in length and have a 25 mil (.025") square cross sec­tion.  Do not use ter­mi­nal strips that have round pins!  The ex­act length of the sol­der-tails isn’t crit­i­cal; some­where around 120 mils (.120") should work fine.  You can ei­ther buy in­di­vid­u­al con­nect­ors with the re­quired num­ber of pins, or just get one long strip – like I did – and cut it up to cre­ate the lengths you need.  You want con­nect­ors with a sin­gle row of pins spaced 100 mils (.100") apart.  Slight­ly “small­er” met­ric head­ers al­so ex­ist with pins that are 2 mm apart; you don’t want those!  Al­so, don’t get con­nect­ors that are de­signed to be eas­i­ly bro­ken apart be­cause they are far too flim­sy and the long­er head­ers would al­most cer­tain­ly break apart un­der the forc­es of in­ser­tion and re­mov­al!

The oth­er parts you’ll need are a 560 ohm ¼ W re­sis­tor and re­place­ments for most of the parts you re­moved from the RF board when you first in­stalled the op­tions.  Don’t try to re­use the orig­i­nal K2 parts be­cause their leads won’t be long enough!  You will al­so need the fol­low­ing tools and sup­plies: a sol­der­ing iron and sol­der, some in­su­lat­ed or bare hook­up wire, di­ag­o­nal cut­ters, nee­dle-nose pli­ers, a small vise, and some bright­ly-colored quick-dry­ing paint.  Don’t use spray paint be­cause it might con­tam­i­nate the con­nect­or con­tacts!  I used or­ange nail pol­ish left­over from Hal­low­een.

  1. Sol­der all com­po­nents and jump­er wires to the con­nect­or tails, nev­er to the posts!  If you are un­able to de­ter­mine the dif­fer­ence … the posts must be gold-plat­ed while the tails should be tin-plat­ed and no­tice­a­bly short­er than the posts.
  2. Nev­er in­sert or re­move an op­tion or an un-mod­ule while the ra­dio is pow­ered on, or even while pow­er is con­nect­ed to the ra­dio!
  3. I haven’t bothered to cre­ate an UN-KAF2 be­cause I don’t have a KAF2 Such an un-mod­ule has to span two K2 mat­ing con­nect­ors, so cre­at­ing one would re­quire a cir­cuit board to prop­er­ly space the con­nect­ors.  (Un­for­tu­nate­ly the sep­a­ra­tion be­tween the KAF2’s mat­ing con­nect­ors isn’t a mul­ti­ple of 100 mils, so stan­dard 0.1" perf­board can’t be used.)

UN-KSB2 Un-Module
Homebrew UN-KSB2

The SSB Adap­tor op­tion can be re­placed by the trio of sim­ple UN-KSB2 head­ers shown above.  When prop­er­ly in­stalled, they du­pli­cate W2, W3, and C167 which you re­moved from the RF board be­fore in­stall­ing the KSB2.

  • 2   3-pin .100" SIP ter­mi­nal strip con­nect­or
  • 1   12-pin .100" SIP ter­mi­nal strip con­nect­or
  • 1   .001 µF ce­ram­ic ca­pac­i­tor
  1. Us­ing quick dry­ing paint, mark pin 1 on one end of the 12-pin con­nect­or.
  2. While the paint is dry­ing, sol­der a jump­er wire be­tween pins 1 and 3 of both 3-pin con­nect­ors.  (Since they are sym­met­ri­cal there’s no rea­son to mark pin 1.)
  3. Af­ter the paint has dried, sol­der the ca­pac­i­tor be­tween pins 7 and 12 on the 12-pin con­nect­or.

Re­move the SSB Adap­tor and plug in the 12-pin UN-KSB2 head­er at J11.  As shown in the silk­screen on the RF board, pin 1 goes toward the left side of the ra­dio when it’s viewed from the front.  Al­so plug in the two 3-pin UN-KSB2 head­ers at J9 and J10.  They are near the right edge of where the KSB2 mounts on the RF board.  ALWAYS INSTALL ALL THREE UN-KSB2 HEADERS (AS A SET) WHENEVER THE ACTUAL KSB2 OPTION IS REMOVED FROM YOUR K2!

If you have any fil­ters con­fig­ured to OP1, they won’t work if the KSB2 is re­moved.  The re­ceiv­er will seem dead if you se­lect one of them.  If you are per­ma­nent­ly re­mov­ing the KSB2 you can use the fil­ter cal­i­bra­tion pro­ce­dure to change them back to use the stan­dard var­i­a­ble band­width fil­ter.

UN-KNB2 Un-Module
Homebrew UN-KNB2

The Noise Blank­er op­tion can be re­placed by the clev­er UN-KNB2 head­er shown above.  In con­junc­tion with the in­stal­la­tion of an op­tion-sup­plied al­ter­nate val­ue for RF-R88, its circuitry duplicates the attenuator that was orig­i­nal­ly formed by the three re­sis­tors you re­moved be­fore in­stall­ing the KNB2.

  • 1   8-pin .100" SIP ter­mi­nal strip con­nect­or
  • 1   100 Ω ¼ W re­sis­tor
  • 1   470 Ω ¼ W re­sis­tor
  • 1   560 Ω ¼ W re­sis­tor
  1. Us­ing quick dry­ing paint, mark pin 1 on one end of the con­nect­or and wait for it to dry.
  2. When in­stall­ing the re­sis­tors in the next step, po­si­tion them ei­ther “above” or “be­hind” the con­nect­or rel­a­tive to the im­age above.  This is im­por­tant be­cause there’s very lit­tle clear­ance be­tween J12 on the RF board and the Elecraft® KSB2 op­tion (when it’s in­stalled).  If the re­sis­tors ex­tend even slight­ly be­yond the “front” edge of the con­nect­or, then their leads might touch com­po­nent leads on the KSB2!
  3. In this step, in­stall the three re­sis­tors by form­ing their leads around the tails of the con­nect­or pins but don’t sol­der them yet:
    1. The 470 ohm re­sis­tor goes be­tween pins 1 and 2.
    2. The 560 ohm re­sis­tor goes be­tween pins 5 and 6.
    3. The 100 ohm re­sis­tor goes be­tween pins 1 and 6.
  4. Now sol­der the re­sis­tor leads.

Re­move the Noise Blank­er and plug in the UN-KNB2 head­er at J12.  As shown in the silk­screen on the RF board, pin 1 goes toward the left side of the ra­dio when it’s viewed from the front.


There are no is­sues re­gard­ing the use of this un-mod­ule.

UN-K160RX Un-Module
Homebrew UN-K160RX

The 160 Me­ters & Re­ceive-Only An­ten­na op­tion can be re­placed by the sim­ple UN-K160RX head­er shown above.  It du­pli­cates jump­er wire W1 (RX An­ten­na By­pass) which you re­moved from the RF board be­fore in­stall­ing the K160RX I haven’t ac­tu­al­ly test­ed this un-mod­ule but I’m con­fi­dent it will work.

  • 1   16-pin .100" SIP ter­mi­nal strip con­nect­or
  1. Us­ing quick dry­ing paint, mark pin 1 on one end of the 16-pin con­nect­or and wait for it to dry.

In­stall­ing the UN-K160RX is more in­volved than the oth­er un-mod­ules be­cause the K160RX is hard-wired to the rear-pan­el RX An­ten­na jack, mak­ing it dif­fi­cult to re­move.  Al­so, note that there’s no pin-1 indi­ca­tor in the silk­screen art­work for J14.  Pin 1 goes toward the left side of the ra­dio when it’s viewed from the front.

Band­pass fil­ter in­duc­tors L3 and L4 are shared be­tween 80 and 160 me­ters so you may need to re­do 80-me­ter trans­mit align­ment af­ter re­mov­ing the K160RX.
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