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  Converting the G.E. MASTR II UHF ‘High-Split’ to UHF ‘Mid-Split’ for use as a Mobile Relay or Duplex Link radio
By Matt Lechliter W6KGB
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By popular demand, the MASTR II edition of the band-split conversion is here! Re-written from the original MVP/Exec II version, it rounds out the ‘top 3’ radios list. The G.E. MASTR II makes a very easy-to-convert, reliable radio in repeater/remote base service when properly prepared. This document is meant to show the procedure for converting these radios to 420-450 MHz operation – full coverage of the U.S. 70cm Amateur band can then be realized. Hence, the need to search for rare (and typically expensive) 406-420 MHz radios (i.e. ‘77’ split) is non-existant. It also provides versatility; the same radio may now be used for either role. Have a link radio that blew up? Swap it out with a ready from your now abundant full-band inventory!


Transmitter Modification Procedures – Exciter Board and Power Amplifier

Parts Required:

Exciter Modifications   (Reference LBI-30564B – ‘Transmitter’ section)

Intermediate Power Amplifier (IPA) (driver) modification:


The transmitter is now modified. Transmitter frequency crystals are ordered as normal. An alternate method is to replace various capacitors on the exciter board, and a table of part values is provided at the end of this document. A high-power (40W+) Power Amplifier deck is rarely necessary in link service. This modification is for the IPA (driver). Modification of the High Power Amplifier is possible, but doesn't necessarily yield ‘to-spec’ results due to its tuned strip-lines (Wilkonson combiner strips), unlike the amplifier decks in MASTR Exec IIs or MVPs.

If your radio has an HPA deck, remove the jumpers between input and output on the HPA, and replace with a coaxial jumper between the IPA and Harmonic Filer assembly.


Receiver Modification Procedures

All changes are performed on the ‘Front-End’/ LO-Mixer Assembly:

Parts Required:

Procedure:

It is highly recommended that one should use high-side injection LO crystals to preclude the requirement to mechanically modify the RX LO/injection cavity assembly.

Note: The 470-494 MHz MVP / MASTR II will allow the use of low-side injection crystals – down to 420 MHz – but the mixer’s tuning screws are nearly ‘bottomed-out’.

High-Side Injection:   Crystal Frequency (Fc) = (Fo + 11.2 MHz) / 27

Low-Side Injection:   Crystal Frequency (Fc) = (Fo - 11.2 MHz) / 27




Table of ‘Exciter Board’ part values

Part Name
(as labeled on
the schematics)
Value before modification
(450-470 MHz) / ‘88’ split
Value(s) with modification
(420-450 MHz) / ‘78’ split
C118 27pF 30pF or add 3.3pF in parallel
C121 27pF 30pF or add 3.3pF in parallel
C122 20pF 24pF or add 3.3pF in parallel
C138 39pF 56pF
C143 39pF 47pF and optionally switch 39pF w/ C193
C192 18pF 24pF or add 5pF in parallel
C193 27pF 39pF or add 12pF in parallel
C194 8pF 12pF or add 3.3pF in parallel
C195 6pF 9pF or add 3.3pF in parallel
L114 .047µH Change to R106 - 10 ohms




Table of Power Amplifier part values

Part Name
(as labeled on
the schematics)
Value before modification (450-470 MHz) Value(s) with modification (420-450 MHz)
C207 8pF 8pF
C208 8pF 8pF
C213 OMIT 5pF
C215 47pF 47pF
C216 43pF 51pF
C217 16pF 18pF   or add 39pF ceramic in parallel*
C224 35pF 41pF
C225 35pF 43pF
C226 43pF 47pF
C227 37pF 43pF
C230 OMIT 7pF
C235 37pF 47pF
C236 35pF 47pF
C238 43pF 47pF
C252 7pF OMIT
C257 OMIT 5pF




Table of ‘Local Oscillator/Multiplier Board’ (Receiver) Part Values

Part Name
(as labeled on
the schematics)
Value before modification
(450-470 MHz) / ‘88’ split
Value(s) with modification
(420-450 MHz) / ‘78’ split
C407 18pF 18pF (NC)
C412 6pF 8pF   (optionally keep C426 and reuse here)
C417 3pF 3pF (NC)
C426 8pF 10pF
C2302 3pF 10pF




We guarantee nothing.   ;)

In actuality, this conversion has proven successful many times over. Try it and see!

Any feedback is always welcomed.


Contributions: Terry Downey – W6TD, Gary Belda – K6ENS (SK), Matt Lechliter – W6KGB

Copyright © 2003 by Matt Lechliter – W6KGB   All Rights Reserved, including that of paper and web publication elsewhere.
E-mail / contact data good in the QRZ.COM database

Original HTML © 25-Jun-2003 Kevin K. Custer W3KKC   All Rights Reserved.


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