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.

Ramblings

Several years ago when beginning my adventure into homebrew electronics, I remember having discussions on how a project would drive other projects.  I came up with the question, “What came first? The project or the test equipment to help build the project?”

Projects built over the years are typical of any homebrewer. The likes of transceivers such as mono band cw rigs of various bands, sdr rigs, wspr, keyers, antennas, pic and Arduino based projects etc. The need for test equipment other than the typical multimeter was recognized quite quickly so homebrew projects for test equipment as well as commercial equipment was acquired. 

Building one’s own test equipment was not only a cost effective way to get sophisticated gear, but it also gave more insight into the circuits they were probing. I built the AADE LC meter, field strength meter, multi-functional probe, sna, signal generator, frequency counter, sweep generator, semiconductor tester, and numerous adapters, bridges, etc to go along with them.  With better equipment, I began to want to take on more sophisticated projects.

As my experience grew, in some cases I began to question what I was measuring and the results that my test equipment was telling me. How accurate were they really and were some of the results being affected by the way I was doing the measurements. Were some of the results fine and was it my interpretation of them the issue?  Of all the measurements I can now make, the one that gives the most difficulty, is the oscilloscope.  

Recently, a problem with noise on a transmitted signal, I discovered that the problem increased when the probe from the scope was attached while making measurements. I also was having trouble making low rf measurements in areas where I really wanted to probe and see what effect the circuit was having on the signal.  Sometimes I could see a signal and other times not.

Now I’m wondering about my measuring techniques with my scope. In particular the passive probes in use and should I build an active probe?  Would this be the answer to some of the problems I’m having?  

So here we go again. (Not complaining) The LBS project has generated additional projects. (This is good) The SNA was deemed to be a must have and the SNA drove about 4 more sub projects to enhance its use. Now its beginning to look like an active probe is going on the list of things to do. 

Who knows for sure, but another project for the list and hopefully a better understanding of electronic circuits will be had. After all, that's one of the things that makes this hobby so great.

73, Peter  

LBS Update 2

Slow progress in tracking down the noise problem.  My glass is 1/2 full so, if I find where the problem is not, then that's progress.

I took out the microphone pre amp completely and the noise remained
Readjusted the carrier along with tx amp and final amp, noise remained
Confirmed good grounds among the various boards
Placed an electrolytic cap at various points and the noise remained
Used tin foil to make a temporary shield for the DDS and Nano boards, noise remained
Use of a battery did not help

So the next step is to solder in caps on all the power points on the various boards and anywhere else one can think of.

As well spent sometime today designing a new circuit board for the pre amp, which includes the AGC circuit. Thanks to Ken VE3ABN, who put together the design for the circuit(s) and got it working.

Looks like I'm going to be cutting it fine getting this rig up and running for Field Day.

73, Peter

LBS Update

Got around to doing a little more on tracking down my noise problem on Tx. The first thing I did was go through the carrier adjustments along with another round of adjustments to the final stage amplifier and Tx bilateral amplifier.  No matter what I do I can't seem to shake the noise.  At times it appears I can but with no confidence that I have licked the problem.

Today I set up my KX3 outside with a 40 meter portable whip antenna and matched the LBS through my HB antenna tuner which is attached to a vertical antenna on the tower.  Set my phone on record and went to the shack and began transmitting.  The results are not really a surprise, lots of noise,  but at least when the LBS was tuned to the KX3 freq. my voice could be heard clearly through the noise.  So at least I can surmise that my circuit for the electret mic is working properly and not the cause of the noise.

Here's a link to listen:  https://www.dropbox.com/l/s/OkepNNEJw5NWnnp6DZMwLr
Comments welcomed.

At this point all intelligent troubleshooting has been done. At least as far as I'm concerned intelligent and now I've resorted to trying anything that can be moved on the boards, well move it.  So I've probably buggered up the BPF a little but that's not to difficult to get back.  I did notice that if I hold onto one of the toroids on the bpf that the noise goes away and the output signal seems to remain. Adjusting the bpf caps can reduce the noise but that's only because the signal is been attenuated. The only other thing I have not tried is to operate the LBS on a battery.  I don't think the power supply is the issue, but you never know.  In fact maybe I should hope it is as the cure is then simple. hihi.

73, Peter

Bunch of Stuff

Been pretty busy these days and shack time has taken a back seat somewhat. Having said that I've got a couple of things on the go. And in no particular order here they are:

1, 2 tone generator.  In order to test the ssb signal on the LBS rig, it has become apparent that I need one.  There are a few kits out there that look pretty good but I was thinking of building one from scratch.  I then stumbled across a kit that produces 2 tones but only one at a time.  For about $4 I figure I can buy two and join the two and see what happens. Turns out there is a local store that carries them so a win win.  Now to find the time to put them together.  I should be able to put them both in one Altoid tin.

2, Get back on the LBS rig.  I have finally all the pieces put together and adjusted.  The only thing to confirm is the quality of the signal.  Injecting a 1khz tone into the microphone amp produces a signal that appears to sound ok.  Speaking into the mic the signal does not appear to be all that great. But to make sure I think I'll remove my KX3 from the shack and move it outside and then get the xyl to speak into the LBS so I can listen to the signal quality.  The LBS is connected to a dummy load so I may only have to move to another room in the house so I can get a clearer picture of the signal.

3, Get the software working correctly for the LBS rig. I like the latest version from Dave, VE3OOI, but am having a few issues getting it to run. None of it insurmountable, but another item on the list. hihi.

4, Work on my cw. Field day is approaching quickly and I'd like to try for a couple of contacts with that mode.  Won't loos any sleep over it if I don't, but I know I'll use it this summer with the gang back in Toronto/Brampton.

5, Get our old "Q4" project up and running again.  It was one of my early ventures into SDR. I think this rig would make for a nice poor mans spectrum analyzer.

6, Start making some more contacts on the hf bands.  After all that is what this hobby is mostly about.  I need to get using my new KX3 more so I can learn and remember all, well most, of its capabilities.  I want to do some outdoor operating this year and the KX3 will be my main rig for that.

7, Raspberry pi.  Got to get onto the board I got 2 Christmas's back and put it to good use.  Couple of ideas but it keeps changing.

8, Load the latest firmware for my SNA.  Some terrific new capabilities with this release and want to give it a go.

Sure there's more but enough writing and time to heat up the iron.

73, Peter