Micom 100 SSB N3ZI DDS VFO?

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Micom 100 SSB N3ZI DDS VFO?

Postby AC5CH » Fri Apr 19, 2013 4:25 pm

I picked up a Micom 100 a while back, and was thinking of putting crystals for 60M in it. However, I was wondering how difficult it would be to use a N3ZI DDS VFO, instead. This would theoretically allow me to use it on 75M, 60M, and 40M. If the filtering has enough "leeway" below 2.0 Mc, I might even get it to work on 160M if I'm lucky.

I understand from reading a previous post that a buffer amplifier will be be necessary to use between the VFO and crystal oscillator in the Micom.

I've got a few questions about doing this:

1. What would I hook the output of the buffer amplifier to? I've used VFOs before, but they were generally hooked up to the crystal holder inside 23-channel CBs I converted for 10 meter use with Siltronix VFOs. Another post leads me to believe that this may not be the way to hook up a VFO to a Micom as the poster said that it would be hooked up to the crystal oscillator, and the channel selector would be used to simply select what filters to use. I'm a bit confused by that...

2. Does anyone know where I can get LSB crystals. My unit only has the USB and AME ones.

3. Has anyone ever done this or a similar procedure on an older crystal unit. If so, I'd really appreciate it if you would share your experiences.

Thanks and 73,

Steve
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Re: Micom 100 SSB N3ZI DDS VFO?

Postby stay-con » Sat Apr 20, 2013 7:04 am

AC5CH wrote: What would I hook the output of the buffer amplifier to?


To start, the DDS is roughly 500 mV into a 600 ohm load.
Various buffer amps from simple to tricky will boost that level to 2-7 V.

There is a Yahoo group for the DDS kits.
http://groups.yahoo.com/group/N3ZI_kits/

Jeff
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Re: Micom 100 SSB N3ZI DDS VFO?

Postby WB6NVH » Sun Apr 21, 2013 1:14 pm

It works fine. You need to build a buffer amp. Crush or remove C99 and feed the output of the DDS buffer via a coupling capacitor to the Q25 side of where C99 was. I think I used 100 pf. The DDS signal is injected at the base of the L.O. buffer amplifier stage, not the crystal sockets or anything previous to that. You then set the range programming DIP switches so that the channel numbers correspond to the correct filter selection for the band in use.

Your best bet is to get the LSB crystals, although shifting the DDS board to be low side injection 11.4 MHz offset will give you the ability to listen to LSB. It will also transmit LSB by doing this, but the signal may or may not have spurious products in the bargain.
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Re: Micom 100 SSB N3ZI DDS VFO?

Postby AC5CH » Sun Apr 21, 2013 6:15 pm

Thanks for the replies and information, guys!

WB6NVH, after reading your post, I located C99 and marked it. I'll be ordering the DDS unit and buffer amp board this week as I really look forward to getting this Motorola on the air. I run Micom 2 units, primarily, but the 100 has a lot of nostalgic charm to it.

Do you have any idea about what the specifics of the LSB crystals are? I don't have a manual, and I wouldn't imagine that Motorola supports these units (information or otherwise), anymore.

Thanks again and 73,

Steve
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Re: Micom 100 SSB N3ZI DDS VFO?

Postby WB6NVH » Mon Apr 22, 2013 10:12 am

If you search Google using Micom 100 there are several good hits. Motorola sold (?) the HF radio division to Mobat some years ago.

One is the full service manual:

http://www.mobat-usa.com/manuals/Micom-100.pdf

The manual should show the Motorola part number for the crystals and International Crystal should have the manufacturing specs on file.

This page gives you more info on crystal manufacturers as well as further Micom 100 conversion data:

http://home.windstream.net/devinsmith/
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Re: Micom 100 SSB N3ZI DDS VFO?

Postby AC5CH » Mon Apr 22, 2013 1:10 pm

Good deal - I have that manual in my files. However, I assumed that the Triton 20 marine manual that came up under the Micom 100 link was a filing mistake by Mobat. I guess they must be the same radio for the most part? I'll definitely give the manual a closer look, now.

Thanks for explaining; I sincerely appreciate it. Due to your help, I'm certain that I'll have the Micom on the air in no time!

73

Steve
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