Converting the G.E. Custom MVP / MASTR Executive II
UHF ‘High-Split’ to UHF ‘Mid-Split’ for use as a
Mobile Relay or Duplex Link radio
By Matt Lechliter – W6KGB

As many know, the G.E. MVP makes a very easy-to-convert, compact, and reliable radio in repeater/remote base service when properly prepared. This document is meant to show the procedure for converting these radios to 420-450MHz operation – full coverage of the U.S. 70cm Amateur band can then be realized. Hence, the need to search for rare (and typically expensive) 406-420MHz 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:
    · (5) – 3.3pF disk ceramic capacitors
    · (1) – 5pF disk ceramic capacitor
    · (1) – 12pF disk ceramic capacitor
    · (1) – 47pF disk ceramic capacitor
    · (1) – 56pF disk ceramic capacitor
    · (1) – 1-Amp/25-VDC – NPN Power Transistor (Jim-Pak #TIP-120 or eq.) – replacing Q215 in the transmitter PA assembly.  (NOTE: The driver PA current exceeds the OEM Q215 rating of ½-Amp; the famous ‘power control transistor’ that commonly fails)

To modify the ‘exciter:’  (Reference LBI-30564B – ‘Transmitter’ section)


Power Amplifier (PA) modification:


The transmitter is now modified. TX 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.

Receiver Modification Procedures – ‘Front-End’/ LO-Mixer Assembly


It is highly recommended that one should use high-side injection LO crystals to preclude mechanically modifying the RX LO/injection cavity assembly. Note: The 470-494MHz MVP will allow the use of low-side injection crystals – down to 420MHz – but the mixer’s tuning screws are nearly ‘bottomed-out.’

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

Table of ‘Exciter Board’ part values
 
 
Part Name
(as labeled on schematics)
Value before modification 
(450-470MHz) / ‘88’ split
Value(s) with modification
(420-450MHz) / ‘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 schematics)
Value before modification (450-512MHz)
Value(s) with modification
(406-450MHz)
C7
8pF
6pF
C8
8pF
6pF
C9
33pF
27pF
C10
27pF
18pF
C11
33pF
24pF
C14
33pF
24pF
C15
47pF
43pF
C16
51pF
43pF
C17
18pF
C22
33pF
24pF
C24
41pF
35pF
C25
43pF
33pF
C26
47pF
37pF
C27
43pF
35pF
C29
33pF
24pF
C30
6pF
4pF
C33
1pF
OMIT
C52
8pF
4pF
C61
33pF
18pF

We guarantee nothing. ;)
In actuality, this conversion has proven successful many times over. Try it and see!

Any feedback is always welcomed.

Copyright © 2003 by Matt Lechliter – W6KGB
Contributions: Terry Downey – W6TD, Gary Belda – K6ENS (SK), Matt Lechliter – W6KGB
E-mail / contact data good in QRZ.COM database
Last html revision Wednesday, June 25th, 2003.
HTML Publishing © June 25 2003 Kevin K. Custer W3KKC
All Rights Reserved.