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Kevin, "Cardinal Rule"...? That was an
excellent write-up that you did...let's have
more of that kind of info on here
How about posting that essay on your RB
website...?
"Well Done"
73 John VE3AMZ
----- Original Message -----
Sent: Sunday, April 17, 2005 9:54
PM
Subject: Re: [Repeater-Builder] GE Mastr
II - what have I got?
Don Pomplun wrote:
Our local volunteer excursion railroad is growing to the point where
simplex radio communications is not filling the need (adding another 3
miles of track, windy railroad, multiple trains). So "going repeater" is
an option. I have seen articles & ads about converting a GE Master Exec II
series radio for repeater operation.
Yesterday I was scrounging around our stash and found a single GE
radio. Maybe you can tell me what I've got and its potential. Name plate
data is:
GE Mastr II
comb MX56KAS66A
ser 8493743SPL
FCC TX Data KT-32-B
FCC RX Data ER-64-A
It would make a fine repeater.
Instructions for doing so are located here:
http://www.mastr2.com/
We also have a number of Motorola Micor series radios, and I'd welcome comments on their suitability vs the GE.
I'll
break a Cardinal Rule here, but since I am doing it technically speaking, here
goes:
First off, I'll tell you that I enjoy converting both the GE Mastr II
and the Motorola Micor Mobile radio sets to repeaters. Both work very
well, and have NO internal desense issues when converted properly. In
all cases the GE Mastr II is an easier conversion, but easier doesn't
necessarily mean it's better. That being said, I do have
favorites. On High-band, 2 Meters and 220, the Micor is my choice,
mainly due to two things; the receiver and the squelch circuitry. For 2M
and 220, we can build a better working receiver from the Micor, and the
transmitter works as well as the Mastr II. On UHF, the Mastr II is my
choice, mainly due to it being conventional in nature. The Micor UHF
mobile is a weird radio; it doesn't have a conventional exciter (Ref 1). It's transmitter frequency is derived from
receiver circuitry, and the Power Amplifier is very inefficient and can be
troublesome. Getting back to VHF, the Micor is a more difficult radio to
convert to a repeater. It's more difficult to convert the RF circuitry,
and it is more difficult to convert to duplex, however ICS Controllers is making
a new controller (the SingleM) to make it easier to do the Micor Mobile to
repeater conversion. This controller comes in response to the NHRC/M2 controllers that make
Mastr II mobile repeater conversion painless.
While the GE Mastr II has
a very wide tuning range, its stability of tuning is compromised as compared
to the Micor. The Micor was built in several 'ranges' in which the
radios were designed to be operated. When operated within these ranges,
the radio will meet or exceed factory specifications; however when operated
outside these ranges, the performance of the radio falls off quite rapidly (Ref 2). On the contrary, the Mastr II will operate
quite well outside of its factory stated ranges. The reason this happens
is in the way the radio sets are designed. The GE Mastr II utilizes
tuning capacitors or trimmer capacitors to tune many of the stages, especially
in the receiver. The Micor uses tuned inductors (coils) to tune most of
the stages, in either the receiver or exciter. By nature, a wider tuning
range is available by using a tuning capacitor, but, at the result of the
stage being touchier to tune right on the money, and the ability of it staying
in tune. This allows a 150.8 to 174 MHz. Mastr II to be used in the 2
meter band or a 450 to 470 MHz unit to be used in the 440 ham band with little
or no 'conversion' of the RF circuitry, but again, at the cost of some
instability. The Micors' tuning is limited by the mechanical range of
the tuning slug. This allows a smoother more precise adjustment of each
stage, but, the Micor *must* be either originally built or 'properly
converted' to operate on the frequency in which it is to be used. This
required conversion makes it more difficult for us to build a repeater from
available surplus commercial radios for the different ham bands, but I feel a
better product results.
I worked in the local Motorola Service Shop
(MSS) in the late 70's and early 80's when the Micor and Mastr II were head to
head competition. I had the opportunity to service both the Micor and
Mastr II during this time; as the local shop was obligated to service whatever
was on the service contract. This is where most of my expertise and
opinion on these two comes from. We had a saying: "One thing you never
have to do is re-tune a Micor, even if it is riding inside a Dragline.
One thing you always have to do is re-tune those [EMAIL PROTECTED] Mastr II's, even if it
is riding in the back seat of a Cadillac..."
I have literally spent
days working on the modifications for both the GE Mastr II and Motorola Micor
for proper 2 meter and 220 operation. It seems I can always make a Micor
out perform the Mastr II where receiver sensitivity is concerned (Ref 3). Although to be quite fair in this statement,
I rarely have the opportunity to use a real 2 meter Mastr II, but may
statement stands on the 220 band. In my opinion, the receiver is the most
important part of the repeater, and a properly working one is a must for the
repeater to operate correctly. The carrier squelch is another item that
must work correctly in a good operating repeater. In my opinion, nothing
beats the squelch operation of the famous Micor Squelch Chip (Ref 4). In fact, the Micor Squelch works so well,
companies have built boards to install in non Micor radios to give them the
same Micor type squelch operation. The Link Comm RLC-MOT is such a board
that we offer as an option to be installed into our GE conversions (Ref 5). As I stated earlier, the UHF is another
story, the GE Mastr II mobile conversion is better, hands down, than a Micor
UHF mobile conversion, although the Micor UHF Station is simply hard to
beat.
These are the basic differences between the two radio sets, and
why I prefer one over the other. While there are other more technical
issues that can determine which radio set I prefer, I won't get into them
unless you want the whole $2.00 tour. Here are some references in the
form of web pages that go into more detail on the things I spoke of in the
text above:
(Ref 1) http://www.repeater-builder.com/rbtip/micoruhfmobile.html
(Ref 2) http://www.repeater-builder.com/rbtip/micorvhfboardnumbers.html
(Ref 3) http://www.repeater-builder.com/rbtip/222sensitronRX.html
(Ref 4) http://www.repeater-builder.com/rbtip/micorsquelch.html
(Ref 5) http://www.link-comm.com/squelch.html
You
did ask, so, I Hope this helps...
Kevin
Custer
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