A Great Day in the Shack with my LBS Rig.

This has being one long project and this is just to get it working.  I want to eventually get around to modifying some of the boards in order to learn in greater detail the various circuits. Eventually put it into a case and go from there.

Somehow I finally have been able to adjust and minimize the carrier, get rid of the noise on tx and adjust the various tx levels to the point where I can put a decent signal on the air.  At least I think it’s a decent signal.  Here is a link to an audio file of the transmission I did an hour ago:

https://dl.dropboxusercontent.com/u/97743994/LBS/LBS%20June%2022.wav

I backed off the mic at around the count of 10 and the audio clears up. There was some background noise in both the shack and outside where the KX3 was located to receive the LBS signal. I’ll do another recording later keeping the background noise in mind. I’m sure I still have some tweaking to do but at least I can now move forward.

As well I’m not completely comfortable yet with the carrier adjustment, but I was able to substantially reduce it and will make some more accurate measurements. In fact measurements all the way round.  I started a document to capture schematics, build notes etc, but got away from it with all the issues I was having.

So it’s looking like I might be able to give the rig a go during field day. Great day in the shack.

73, Peter

LBS Rig Noise Update

Well, that was fun.  I found 2 flaky sma cables, one bad power pin for the relay 3 board, and a loose power pin on another board.

The shack and the rig is a big mess. Wires, test gear, parts all over the bench. In fact I spread out over 3 benches.

The good news is I think I’ve licked the noisy signal issue.  Got rid of all the 12v return lines and the ground loops and go figure… no noise.  The carrier adjustment is better as well.  Not quite so sharp.  I don’t like the fact that the shield is no carrying the 12v returns to ground, but I didn’t have much choice.  

The design of this rig was chosen so I could easily replace individual circuits/modules as I learned about them and may have made some improvements in the design.  I didn’t realize at the time that the design would create problems. Ie the ground loops.  Another problem I found was my choice of rf cables.  I went with pre-made sma cables and that was not a good idea.  They are not the best when used in tight spaces.  Sharp bends and loops are needed and this has put pressure on the connectors and this has made for intermittent connectivity.  Next time I’ll make my own cables and use RG174.

So tomorrow I’ll set up my KX3 again in the backyard and record the transmissions from the LBS rig.  Last time lots of evidence of ground loop noise and this time, let’s hope no noise.  Preliminary testing suggests no noise.

Here's a picture of the LBS rig in its present state.  If it proves to be quiet, then I'll clean up the cabling.

 

Time to Let The Smoke Out? not.

After spending sometime removing several 12v return lines, relocating some 12 + lines, breaking 2 pcb traces, 12v distribution wiring all over the place, its time to power up. I've been quite lucky with the letting out the smoke club with this project and now's not the time to re-up.  Hopefully this settles down the noise issue and it would be just great if somehow the carrier issue is related.

One thing that has shown some weakness in this latest endeavor is how incomplete my documentation is.  As well as I thought I did, more is needed. Of course this only comes to light when you are ripping things apart and then putting it back together over a period of a couple of days and you begging to question why something was done a particular way.

Ok, enough delay, time to turn the switch on.

73, Peter

LBS Noise Update and Ground Loop Revelations

I’ve been convinced.  I have ground loops.  In fact I have so many it’s hard to count how many.  So this called for some further reading. (ohoh) Reading a few different points of view on the subject was enlightening and I came across some interesting things.
 

In summary and for consideration, here are couple of points:

1, when mounting rf connectors on a pcb, create a separate ground plane running around the perimeter of the board.  Make one connection to this plane at one end of the board near where the main ground has been established.

2, when using coaxial cable on a board, ground one end and leave the other end open.  This will allow any noise picked up by the shield to run in one direction to the ground and not create a loop.  The loop being the shield and the chassis.

Thoughts:

I can see where there are considerations to account for depending on the style of construction used.  Multiple boards will be built one way and if using just one main board, then point 2 will come into play.

Early on I was not comfortable with the thought of the shield carrying the return for the 12v system. This is why I ran the twisted pair to each board for the power.  I did not realize that its loop itself that can cause the noise. Not just some wire picking up noise from somewhere else.  I thought this to be most interesting.

Making good bonds to the ground plane does not eliminate the possibility of creating a loop.  The difference between the characteristics of a cable, copper trace, or chassis is enough to create the loop.

I’ve now come to the understanding that when building a radio, no matter what the subject is, it can become complicated at times.  Doesn’t really take away from the fun, but can cause some frustrations none the less.

So over the next couple of days I shall start removing the various 12v return lines and allow the rf shields to supply the return.  This should eliminate all the loops in my setup.  Once that is cleaned up then back to the carrier issue. I've designed another mixer board if I end up not being able to control the carrier.