[aprssig] E Coast 9600 baud backbone 15W radios.

[Stephen H. Smith]

On 5/27/2016 11:31 AM, Robert Bruninga via aprssig wrote:
> At Dayton I picked up a box of 25 UHF data radios for the E Coast 9600 baud
> backbone project.
>
> Turns out, they are on 824 MHz.  But they have a 15 W driver stage that can
> give us 15 Watts in the 420 MHz amateur band if we can find a simple UHF
> transceiver with 1 Watt output.  ALl we have to do is bypass the final 45W PA
> and add a TR switch.
>
> Then add a TNC node and we are done.
>
> See the info on these radios at the bottom of this page:
> http://aprs.org/ec9600net.html
>
> So, does anyone have ideas for the 1W UHX XCVR that we can split out the TX and
> RX separately so we can use these PA's?
>
> The data radios include a GPS receiver, but we wont need thoes in this application.
>


These are the same French-Canadian-made radio modems (the manufacturer 
"DataRadio" is located in Montreal, Canada)I deployed for Southern California 
Gas Company nearly two decades ago.  DataRadio's main stock in trade is the 
modems themselves.  In your case, the modems are embedded inside a generic 
800/900 MHz FM transceiver.  They were intended for full duplex operation with 
a mobile phone duplexer; hence the separate RX and TX antenna ports.  The 
duplexer in question was originally designed for very early trunk-mount 800-Mhz 
cellular "car phones" that existed before the Motorola "DynaTAC" hand-held 
cellphone caused the entire cell industry to migrate to hand-set phones.

In my case, for a 900 MHz mobile data network for dispatching gas company 
service workers over half the state of California, the modems were in external 
boxes similar to a KPC3 referred to as an "MRM" (mobile radio modem). They were 
mated to a standard Johnson 900 MHz FM SMR trunking transceiver programmed for 
a single channel.

The base stations, located on 13 of the highest mountaintops in Southern Cal, 
were 100-watt Johnson SMR trunking base stations modified for single-freq 
operation. In turn, they were mated to DataRadio's base station TNC-like device 
that they called a "BDLC" (base data link controller). These modems used a 
4800-baud DPSK modulation scheme with proprietary higher-level link protocols 
layered on top.

Using these now-obsolete (road kill on the FCC's forced march to 2.5KHz 
deviation/12.5 KHz channels for ALL non-ham users) 800 MHz data radios for ham 
applications sounds like a insanely  inefficient kluge, unless you can move 
them as-is to the 900 MHz band and use them as-is.

By the time you come up with a separate low-level transceiving exciter, the 
necessary DPDT coax relays (required to insert the salvaged 400 MHz driver 
stage "PA" inline on TX and bypass it on RX) and the necessary low-pass filters 
on the "PA" output (the driver was never intended to be connected directly to a 
live antennna), and then repackage this sprawling mess in a reasonable cabinet, 
you will have spent far more than for a generic Chinese dual-band VHF/UHF 
transceiver ready to go.

[There are now 10W and 25W Chinese dual-band VHF/UHF FM transceivers 
ready-to-go available on eBay and elsewhere for $60-$90 NEW!]

These radios are targeted at dual-use markets (commercial land mobile -AND- 
amateur). They don't have "VFOs" like ham rigs -- just a very large number of 
fixed memory channels available that need to pre-programmed with PC-based 
software via serial-port contacts in the mic jack.  Just program one of these 
devices with a single UHF channel and you're good-to-go.  And they work 
anywhere from 400 to 500 MHz on UHF.

Some of the 10-watt units are small enough to fit into the 5" drive bay of a 
standard tower PC.  I'm about to package one of these into a Dell mini-tower to 
create a self-contained digipeater/igate/web-server "APRS Appliance" on normal 
144.39 VHF APRS that needs just antenna, Internet and power.

The remaining challenge is whether the PC's +12 VDC line can supply enough 
current (about 2 amps) on TX to avoid another DC power supply.    [With the 
CD/DVD drive removed and an ultra-low power SSD drive replacing the original 
3.5" spinning hard drive, I think I will have enough 12 VDC left over to power 
the radio.]