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[aprssig] Re: Mic encoders

Stephen H. Smith wa8lmf2 at aol.com
Sun Oct 2 23:54:15 UTC 2005

scott at opentrac.org wrote:
> I still haven't decided if I want to include connectors so it can be used
> like a Mic-E.  Does anyone still want or use such a beast any more?  Are
> there many Mic-E gateways left?
> I may add it just so Search and Rescue users have a nice integrated option,
> but I'd prefer not to have to deal with lots of pinouts and mic connectors.
> I'd likely just set it up with the Kenwood RJ-45 mic pinout.
> If there's really a market for it, I'd consider adding the 8-pin circular
> connector and jumper matrix like the Mic-E had.  I just don't want to make
> it more expensive than necessary if not many people want that.
Some random thoughts on these issues.........

1)  Aside from Mic-E operation (which I have a definite interest in, in 
connection with my APRN combined SSTV & APRS projects),  having the 
Mic-E potential (having passthrough from the mic, through the box to the 
radio) is useful. 

It makes installation on a single radio that is shared between use on 
APRS, and use on a voice channel, a lot simpler, since you don't have 
keep plugging and unplugging stuff (i.e. swapping beween tracker and mic 
if you DON'T have the mindin-6 connector on your radio.).  Just turn off 
power to the the Opentrac when you aren't doing APRS.

[ BTW, I am providing Mic-E gateway service to the 146.700 Sunset Ridge 
repeater that overlooks most of the greater L.A. basin.    Lookup findu 
for "146.70"  ]

2)  The round 8-pin connectors are a lot easier to wire than RJ-45s , 
especially if you are using round shielded multi-conductor mic cable 
instead of the usual unshielded CAT5 LAN cable.  [ Have you ever tried 
to corral the multiple soft flexible stranded conductors and shield of a 
mic cable into an RJ45 plug to crimp it? ]   If you have a radio with 
the RJ-45, one can always cut a short LAN patch cord in half, and solder 
the bare ends to an 8-pin plug to make an adapter pigtail,  

Adapting in the reverse direction (adapting a  mic with a round plug to 
a box with RJ45s)  is much clunkier. First you have to get one of the 
hard-to-find INLINE 8-pin mic jacks.  You CAN attach a half lan cable to 
it, but the in-line jack, encased in a machined metal cylinder, becomes 
a heavy pendulum swinging, swaying and tugging on the RJ45 plug at the 
entrance to the encoder.  Not to mention the weird mechanical resonances 
that occur between the mass of the jack and the springiness of the curly 
mic cord.  Much better to have the 8-pin plugs securely mated to a box's 
panel than flopping round in mid-air.    

[ I  DO admit, that from your (manufacturing) standpoint, the round 
jacks are more work since they usually have to be mounted with a hex nut 
to the case with short wire leads then soldered to the PCB, compared to  
RJs which can be mounted directly to the PCB.  I suppose you could use 
PCB-mount 8-pin jacks on a double sided PCB with with one sticking out 
from each side.  The resulting package shape factor would resemble an 
iPod with the mic plugged into one face and the cables to the radio and 
GPS on the other. ]

3)  I would suggest not having a multitude of pinout configuration 
jumpers inside the box.  Make the accommodations for different TX audio, 
PTT, DC and common/GND pins (for different radios) outside the box,in 
the cable assemblies instead.  This way, you can quickly move the device 
among different radio makes and models by changing connecting cables, 
rather than by opening the box and fussing with jumpers.   [ I am 
envisioning that an organization could have a pre-programmed pool of 
these devices with an assortment of cables to instantly mate with 
various members Kenwood, Icom and Yaesu radios as needed. ]  

However, if you go with the RF45 connectors on the device, the config 
jumpers will probably be inescapable because users are going to want to 
use standard ready-made straight-through LAN patch cords to connect the 
box to the radio. 

4)  If the TX audio (tone) level is controlled by hardware rather than 
software, place the trimpot on the PCB in a way that it can easily be 
turned through a hole in the case without having to open up the box.  (I 
suspect that a lot of the wildly over- and under- deviated signals one 
hears are due to the difficulty of making TX level adjustments once the 
devices are packaged and installed in a mobile.)

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Skype:              wa8lmf
Home Page:          http://wa8lmf.com

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