Modification of MICOR Low-Band Mobile and Station Exciter
and Harmonic Filter
for use in the 6 meter Ham Band

By Kevin K. Custer  W3KKC
with excerpted conversions from KB6MIP

Concept:
To modify a Motorola MICOR Low Band 42-50 MHz. split Base and Mobile type exciters and harmonic filter for use on the 6 meter amateur band.

Exciter Modification Description:
This modification involves altering component values in the multiplier circuitry.  It does not change the multiplier of either the Mobile or Station exciters.  This modification will provide original power output from the exciter (400mW).  Additional information is provided for tuning the harmonic filter for use in the 6M amateur band.

General Exciter Information:
The MICOR Mobile exciter is different from the Station exciter. The MICOR mobile uses a TLB816x / TLB683x series exciter and uses a K1004 channel element with a x3 multiplier.  The MICOR station uses a TLB817x / TLB827x series exciter and uses a KXN1028 channel element with a x6 multiplier.  The KXN1028 channel element used with the station exciter is capable of true FM modulation. In most situations and applications, the two types of exciters can be used interchangeably; a station exciter can be used in a mobile and vice-versa.  Due to the difference in the multiplication factors between the two exciters, the channel elements will only work with the type of exciter they were designed for.

MICOR Mobile Exciter Conversion:

Note: Be certain the exciter operates correctly on the origional frequency before attempting to modify it for the new band.  You may want to document the output power of your particular unit, using your test equipment, so you know what to expect after the conversion is done.  Please read through these instructions to become familiar with each procedure before attempting the conversion.

Component Replacement:
Remove and replace the following components with the values indicated.
Replacement capacitors should be of the same type and style as the original.

Reference: 42-50 MHz Exciter schematic (TLB816x / TLB683x) design center freq. at 52.525.

Components Required:
Disc capacitors: (2)2.0, 10, 12
Silver-Mica capacitors: 34, (2)43, 56, (2)100, 220, 330
1/4W resistors: 12K, 18K
For a complete kit of parts needed, please e-mail n3xcc at repeater-builder.com for more info.

Change listed components to the following values: (all caps in pF)

All capacitors are silver-mica unless otherwise noted.
* = capacitor gets reused in another location if 42 - 50 MHz split is being converted

C419 - 100 - use old C445
C421 - 10 - disc
C424 - 2.7 - disc - use old C446
C425 - 12 - disc
C427 - 100
C428 - 13 - disc
C430 - 100
C432 - 5 - disc - use old C439
C434 - 330
C435 - 220
C438*- 75 - use old C452
C439*- 3.3 - disc - use old C453
C441 - 90 - use old C444
C442 - 220 - use old C456
C444*- 56
C445*- 62 - use old C455
C446*- 2.0 - disc
C448 - 34
C449 - 110 - use old C438
C451 - 90
C452*- 43
C453*- 2.0 - disc
C455*- 43
C456*- 150 - use old C451
C459 - 150
R431 - 12K
R424 - 18K

Tune the exciter as per the Motorola manual.
You should be able to obtain original power output on the new band.

MICOR Station Exciter Conversion:

Note: Be certain the exciter operates correctly on the origional frequency before attempting to modify it for the new band.  You may want to document the output power of your particular unit, using your test equipment, so you know what to expect after the conversion is done.  Please read through these instructions to become familiar with each procedure before attempting the conversion.

Component Replacement:
Remove and replace the following components with the values indicated.
Replacement capacitors should be of the same type and style as the original.

Reference: 42-50 MHz Exciter schematic (TLB817x / TLB827x series) design center freq. at 52.525.

Components Required:
Disc capacitors: 75
Silver-Mica capacitors: 24, 27, (2)43, 51, (2)75
For a complete kit of parts needed, please e-mail n3xcc at repeater-builder.com for more info.

Change listed components to the following values: (all caps in pF)

All capacitors are silver-mica unless otherwise noted.
* = capacitor gets reused in another location if 42 - 50 MHz split is being converted

C430 - 80 - use old C461
C432 - 160 - use old C433
C433*- 140 - use old C441
C438 - 24 - should not change - verify to be sure
C440 - 30 - use old C452
C441*- 51
C444 - 75
C445 - 43
C448*- 24
C449 - 120 - use old C453
C452*- 27 - use old C448
C453*- 110
C454 - 2.0 - a 2.2 is installed. For most applications, that should be close enough.
C456 - 27
C457 - 43
C459 - 75 - disc
C461*- 75

Tune the exciter as per the Motorola manual.
You should be able to obtain original power output on the new band.

Filter Modification Description:
Reference 42-50 MHz Harmonic filter (TFB6024A).

As built, presents unacceptable swr to MICOR PA.  Spread or pull coil turns apart to raise bandpass to 6 meters. Test by measuring power or checking swr or using sweep generator or all three.

Notes:  Some of these cap values are hard to find.  Some of the oddballs can be found in other boards of different ranges.  For a complete kit of parts needed, please e-mail n3xcc at repeater-builder.com for more info.

Mobile conversion information by Kevin K. Custer W3KKC
Station conversion information excerpted from KB6MIP's Website, T71.exe file.
Original Copyright 1-26-1998 Kevin K. Custer  W3KKC   
Updated August 31, 2007 to repair broken link to KB6MIP.
Updated September 05, 2009 to correct parts lists. N3XCC.
Any Comments? Send them here   e-mail Kevin

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors.   All Rights Reserved, including that of paper and web publication elsewhere.

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