Critical App Notes!

IMA: When NOT to Apply External Bias

9 May 2008 – In a recent Reflector post Don Wilhelm (W3FPR) wrote …

The two types of microphones commonly used with am­a­teur ra­dio equip­ment are electret and dynamic.  These terms re­fer to the prin­ci­ple on which their trans­duc­er (ele­ment) op­er­ates.  The out­put of an electret trans­duc­er is in­her­ent­ly low, so electret mi­cro­phones al­ways in­cor­po­rate a built-in pre-ampli­fi­er.

In contrast, the output of a dynamic trans­duc­er is nor­mal­ly suf­fi­cient for use with mod­ern solid-state trans­ceiv­ers, with­out the need for a pre-ampli­fi­er.  As a re­sult, pre-ampli­fied dynamic mi­cro­phones are rare­ly en­coun­tered.

Regardless of its type, if a microphone has an internal pre-ampli­fi­er, then it needs to be pow­ered some­how.  In am­a­teur ra­dio ap­pli­ca­tions, this pow­er is pro­vid­ed in one of two ways:

Dynamic microphones rarely have a built-in pre-ampli­fi­er, and most that do are bi­ased in­ter­nal­ly.  How­ever, a very small num­ber of pre-ampli­fi­ed Icom dynamic mi­cro­phones do re­quire ex­ter­nal bi­as­ing.  If your dynamic mi­cro­phone does not have cir­cuit­ry to pro­tect its trans­duc­er, then mis­tak­en­ly ap­ply­ing an ex­ter­nal bi­as will damage it!

The best way to ensure that you are properly con­fig­ur­ing the IMA jump­ers is to “know” your mi­cro­phone(s).  Yes, the PDF User’s Guide will get you start­ed.  How­ever, much of its con­tent is de­rived from in­for­ma­tion that has not yet been ver­ified by hands-on test­ing.  So your saf­est re­course is to know the ele­ment type, pin-out, and bias re­quire­ments of your mi­cro­phone(s).

In addition, many other microphones (and headsets) beyond those listed in the User’s Guide can be used with the IMA, provided that you know how to.

IMA: Do Not Remove the “Built-In” Spacer

29 February 2008 – In December 2007 we learned that – while re­mov­ing the rem­nants of the break­away tabs – one of our K2 In­ter­nal Mic Adap­tor (IMA) cus­tom­ers had also mis­tak­en­ly re­moved the built-in spac­er on the left edge of the Mic Patch Panel board.  At that time, we ad­dressed this is­sue by further em­pha­siz­ing the im­por­tance of this spac­er in the IMA Quick Start Instruction Sheet (QSIS).  More re­cent­ly we learned of a sec­ond oc­cur­rence of this as­sem­bly er­ror, prompt­ing us to raise this is­sue to the lev­el of an app note.

Most likely there was no mention of the im­por­tance of this built-in spac­er in the beta re­lease QSIS that ac­com­pa­nied our in­itial (Sep­tem­ber 2007) IMA de­liv­er­ies.  This spac­er en­sures that that the IMA can­not slide off the K2’s Mic Con­fig­ura­tion header (FP-P1).  One cus­tom­er re­port­ed that with­out the spac­er, the en­tire as­sem­bly had even­tu­al­ly worked it­self loose.  This is more likely to oc­cur if you op­er­ate in a high vi­bra­tion en­vi­ron­ment with the tilt bail ex­tend­ed.  It may also be more like­ly to oc­cur if you fre­quent­ly re­con­fig­ure the jum­pers, due to the re­sult­ing lat­er­al forc­es on Mic Ex­tend­er sock­et J1.

If you received your IMA kit prior to Jan­uary 2008 but have not yet as­sem­bled it, you should down­load and use the lat­est IMA QSIS to en­sure that you don’t over­look this im­por­tant point dur­ing as­sem­bly and in­stal­la­tion.  If you in­stalled your IMA be­fore Jan­uary 2008, please in­spect your Mic Patch Pan­el board and verify that you did not mis­tak­en­ly re­move this spac­er.  If you did, then please contact us to make ar­range­ments to re­place your IMA.

Rev. G Headers Board: Resistance Checks

17 September 2006 – The expected UN-KNB2 (J12) head­er board re­sis­tance meas­ure­ments are trans­posed in the Quick Start In­struc­tion Sheet (QSIS) that was in­clud­ed with in­itial ship­ments of our new rev. G Head­ers kit.  Our latest QSIS has the cor­rect val­ues, which are re­pro­duced here …

Rev. D Headers Board: RF-L4 Access

2 September 2005 – An issue has been iden­ti­fied where the rev. D UN-K60XV head­er board par­tial­ly blocks the adjust­ment slot of L4 in the 80/160m band­pass fil­ter (as shown be­low left).

To alleviate this obstruction, we recommend cutting a small notch in the board (as shown above right).  This may be eas­ier to do be­fore pop­ula­ting the board with parts.

Rev. D Headers Kit: Longer UN-K60XV Connector Pins

30 August 2005 – Do not install the originally supplied (short) male connectors on your UN-K60XV!

An issue has been identified with regard to the male con­nec­tors in­clud­ed with your kit.  In or­der to clear band­pass fil­ter in­duc­tors L2 and L4, the UN-K60XV re­quires con­nec­tors with long­er pins than were orig­inal­ly sup­plied.  There­fore, please use the en­closed con­nec­tors with 318 mil con­tacts for your UN-K60XV.

If you purchased our “Headers PCB” (as opposed to our “Headers Kit”), please note that the UN-K60XV re­quires male con­nec­tors with long­er contacts.