[DSP-10] 1296 RSU -- more lessons learned

[Courtney Duncan]

I monitored all week without hearing anything, or seeing anything that  
turned out to be real in the spectrum display.  This after solving the  
intermittent on/off problem.  It was a cold solder joint on the crystal.

Hooked up the transverter output straight to the counter.  Key up or  
key down it said 1460.0 MHz.  This agrees with seeing 20 mW output key  
up or key down (PTT down) but isn't right!  Hmmmm.  Played with the  
number 1460 for a while.  It's 22-3/16 of 64 MHz, exactly.  A red  
herring?

Opened it up and eventually discovered a short on the 1152 line from  
the LO to the transverter.  Took out the jumper and put in some of the  
connectors I bought with the project, using a real SMA - SMA jumper I  
got out of the trash somewhere about 15 years ago.  This took longer  
than necessary because I put the connector on the LO board on the  
wrong side for mounting clearance, had to cut it off and start over.    
See desperate plea for mechanical advice this below.  Now I can  
measure 1152 after A5 again, explaining that mystery.

That fixed things.  Transmitting, receiving, and counting as expected  
once again.

Didn't hear the local 1296.100 net Friday night at 2000 local,  
however.  Hmmmm.

Wondering if it might be the antenna, hooked up the HT and scanned the  
entire band for a couple of days.  Nothing.  This morning while  
working on the 1296 RSU with the outdoor antenna, continued scanning  
with the HT on the HT antenna indoor, the SRH999.  After a few hours,  
suddenly there was a full-scale, full-quieting repeater QSO.  Switched  
to the outdoor antenna and could only barely hear the QSO in noise  
after opening the squelch.  That's like 40 dB difference, an indoor HT  
antenna better than an outdoor antenna.  The discone / 9913 feed works  
OK on 147 and 445 MHz, for nearby repeaters anyway.  This 1283  
repeater is about 20 miles away on a hilltop.  Unfortunately the IF  
rig (DSP-10) won't tune down to 133 to look for this.  Must find a  
real customer between 1295.5 and 1300 MHz.

So it's the antenna.  The discone / 9913 is about 1.5:1 on 1296 but  
is, as we say, "an air cooled dummy load," when it comes to getting out.

Now I'm monitoring on the 1296 RSU with the SRH999 sticking straight  
up off the box directly here in the house, just like the HT was.   
Haven't heard any amateur activity yet, aside from myself, but have  
heard the SSSSSS again.

Then I made some measurements:

DC input at 12.0 V.
148 mA RX
185 mA TX
185 mA key down

about two watts input.  (1% efficient, HI)

Noise figure:  20.4 dB as measured with my Sabin noise source at 20 V.

Besides sloppiness (cold solder joints, shorts on coax jumpers) I've  
suffered greatly on this project from mechanical ineptitude.  The  
drill press helped a lot with drilling nice holes, but it doesn't fix  
the problem of deciding where to drill them.  Someday I'll expand with  
an amp / preamp / real antenna and may repackage.  Anybody have any  
hints about how to:

- choose a box for something like this
- position boards in it
- wiring harness
- place connectors
- ?

so that NOTHING interferes mechanically with anything else, or creates  
an electrical hazard?

73 and thanks,  Courtney, n5bf/6


"It's science. They don't know anything; they just make a lot of  
educated guesses."  -- Viannah Duncan

Courtney Duncan, n5bf/6
cbduncan at earthlink dot net
144.200, 7.040.
n5bf at amsat dot org