CDM1250 Channel steering

Josh · Post by **Josh** » Fri Dec 08, 2006 7:01 pm

I'm looking to have channel steering on my CDM1250, but the problem is unlike the GM300 there are only 4 channel steering pins as opposed to 5 on the GM300..

Since I can program on the CDM pins 1-4, is the 5th one ground?

-Josh

Post by **HumHead** » Fri Dec 08, 2006 7:31 pm

The CDMs only have four channel steering iputs, allowing you to steer up to 15 channels (technically you could do 16 by leaving the radio on channel 16 with no pins asserted, but that's a little short on reliability).

The pins can be set in CPS to either reference Gnd or V+

RKG · Post by **RKG** » Sat Dec 09, 2006 8:24 am

The wrinkle with the CDM channel steering pins is that they are binary coded, so you need some way to encode them.

We not too long ago did this with a Quantar. Station was to be a multi-channel portable repeater in a huge Pelican-style case (with wheels!). In lieu of jury-rigging some form of TRC to handle channel selection, we used a Binary coding pushwheel switch from Mouser (sku 106-9904) and it worked like a charm. Binary channel selection within the Quantar was handled by wildcard programming.

jackhackett · Post by **jackhackett** » Sat Dec 09, 2006 9:29 am

What are you going to be using to select the channels?

Post by **HumHead** » Sat Dec 09, 2006 12:09 pm

Remember- There are 10 kinds of people in the world- those who understand binary, and those who do not.

Josh · Post by **Josh** » Sat Dec 09, 2006 12:28 pm

jackhackett wrote:What are you going to be using to select the channels?

I figured the channel steering worked with having certain pins grounded and others not. So, if you wanted to be on channel one, you'd have 0001 over the 4 pins, as in only one of them gets grounded. If you want channel 15 then all four would be grounded- or setup on some sort of channel return.

What I want to be able to do is select certain channels remotely via relays and diodes, so let's say relay one set the radio to channel 1, I'd just have to make sure the proper pins got grounded.

I know the channel steering isn't the same as say the Micor, but if it's even more complex than the GM300 then I may run into some problems.

-Josh

Post by **HumHead** » Sat Dec 09, 2006 12:39 pm

Your understanding of the functionality is correct. You could either use your approach, or a binary coded switch, as RKG suggested.

Josh · Post by **Josh** » Sat Dec 09, 2006 2:59 pm

HumHead wrote:Your understanding of the functionality is correct. You could either use your approach, or a binary coded switch, as RKG suggested.

Well for my simple application of a DTMF powered four-relay device, and a bag full of diodes, they'll work

Anyhow, where can I find a channel steering table? -or- if I can't, does pin one correspond with 0001 if no other pins are grounded?

-Josh

Post by **HumHead** » Sat Dec 09, 2006 3:17 pm

You were correct above in understanding that the pins form a representation of the channel number in binary.

So:
Channel Select 1 = 1 (2^0)
Channel Select 2 = 2 (2^1)
Channel Select 3 = 4 (2^2)
Channel Select 4 = 8 (2^3)

If you assert Channel Select 1, the radio will steer to channel 1
If you assert Channel Select 2, the radio will steer to channel 2
If you assert Channel Select 3 + Channel Select 1 simultaneously, the radio will steer to channel 5 (4+1)
...and so on up until you assert all four Channel Select lines to get channel 15 (8+4+2+1)

If none of the Channel Select lines are asserted, the radio will default to the last channel selected from the front panel, effectively allowing you to choose 16 channels.

jackhackett · Post by **jackhackett** » Sat Dec 09, 2006 5:11 pm

A diode matrix is exactly what I was going to suggest. For switching four channels from relays you can get away with just 2 diodes, connect the first relay to channel select 1, the second relay to channels select 2, the fourth relay to channel select 3, and the third relay to both channel selects 1 & 2 through a diode to each.

You could also just connect each relay to one of the four lines, and then program the radio so your four channels are in positions 1, 2, 4 and 8.

Of course if you want to do more than four channels it gets a bit more complicated. Also, if you wanted to control it with a tone remote panel, CPI makes a ten channel one that outputs BCD, I think it would be able to control the CDM directly, IIRC it's model TTP216.

RKG · Post by **RKG** » Sat Dec 09, 2006 6:53 pm

HumHead wrote:Remember- There are 10 kinds of people in the world- those who understand binary, and those who do not.

And what is the decimal equivalent of Fh?

Post by **HumHead** » Sat Dec 09, 2006 7:07 pm

RKG wrote:And what is the decimal equivalent of Fh?

Sorry, I took that one hook, line, and sinker once already!

Josh · Post by **Josh** » Sat Dec 09, 2006 9:35 pm

HumHead wrote:
RKG wrote:And what is the decimal equivalent of Fh?
Sorry, I took that one hook, line, and sinker once already!

I intend on steering to channels 16, 15, 1 and perhaps something else, but 16 is going to be a "auto-scan" mode so I can have that feature available as well, and default to it when/if something fails.

I see how it works though, this should work out and be fun.

Thanks a lot guys

-Josh

RKG · Post by **RKG** » Sun Dec 10, 2006 10:58 am

HumHead wrote:
RKG wrote:And what is the decimal equivalent of Fh?
Sorry, I took that one hook, line, and sinker once already!

We should do that again. (Alex: are you copying?)