A few fun things

A little busy these days but managed to get some good shack time here and there and accomplished a lot.

First up is I finally got my xtal filter board working properly.  Turns out, and to make a really long story short, I had one of the transistors for the receive amplifier in backwards. Wouldn't you know that it was pretty much the last thing I checked.  Anyway, looking back at the bench once I fixed the problem and saw the mess the ensued, I had to post a picture.  Takes a lot to troubleshoot and repair a board sometimes. Everything you can see was used except the vtvm.  Missing in the picture are signal generators that were used as well.



Next up was a look at the microphone amplifier circuit and a mic to use.  I was going to use a mic from an old marine vhf radio I had that I'm junking. But I think I'll go with a Yaesu MH-48 that I have spare.  In fact I have one with a broken ppt button and a complete spare one as well.Might be able to jury rig something for the ppt button that will work.
The only mod needed to have a basic mic will be shorting out a resistor and diode in the ppt circuit. Circled in blue, middle right. And adding a 9v regulator to the amplifier board.  I think I'll add as well some spare traces and connections in case I decide in the future to utilize some of the buttons on the mic.  LSB/USB switch comes to mind for starters  Frequency up and down might be nice as well.   Going to be a little more complicated with this one though.  It appears that Yaesu uses different voltage levels on two lines to determine which function or button has been pressed.  I've messed around a little with the Arduino before in order to determine different voltage levels so it should not be too difficult.  I'll laugh now.

An finally, almost there as an operational ham.  Proof is in the picture.  Antenna coax is in the house. I'll be working on the grounding system in the next few days or so.  Great wx right now for sure.  The hole in the brick took all of about 1 minute. I rented a rotary drill and 1.5" core bit.  Worth every penny.  Or should I now say nickle.  Nothing like using the appropriate tool for the job. 
Lots of room for another coax or 2 and ground.  It is a 2" hole in the header but 1.5" in the brick.

The complete antenna system at ve3poa

Prelim Analysis of the R5

Here's the sna plot of my R5. Not the best looking so far.  The plot run was from 7mhz to 30mhz so I may need run a more defined span of frequencies in the area of interest only.  For another day though.

Antenna Install

Getting closer to being a "real"? ham now.  The R5 went on top of the tower this afternoon. Just have to drill a hole through the brick wall to get the coax into the shack.  I guess I'll do that next week or maybe Sunday.  Looking at the last picture, I'd say not too noticeable.....XYL says different. hihi

 

 

Control board

Pretty good couple of days in the shack.  Got a good handle on the xtal filter board and finished off the DDS control board today.  Installed the 9v regulator, 2 electrolytics and a lot of 104 bypass caps. Put in the 12v connector and have to remember that I reversed the polarity on the bus on that side of the board. Put a dab of you know whose red nail polish on the new + bus.  Well, at least as far as hardware is concerned I should be finished.  I still have an issue with the read-out and hoping its a contrast setting in the software.  The lights blink on the Nano and there is output on the Si5351 board, so that's good news.

Now just to relearn the Arduino stuff and onward and upward.

73, Peter

Scope readings for the Crystal Filter & Bilateral Amplifier Board

Crystal Filter and Bilateral Amplifier Board

This document will outline the Lets Build Something Crystal Filter Bilateral Amplifier board. Included are several screen shots of the circuit taken into account both Tx and Rx modes.

One of the concerns I have is the effect the circuit has on the input signal.  I’ve included spectrum analysis where appropriate for consideration.  As well I have concerns with the Rx mode and will need to look into this further.

Input signals were adjusted to 1Vpp as per the reading on the scope. The signal generator amplitude needed to be adjusted in order to accommodate the different effect that the 2 input connections were having on the generator.  Frequency used was 4.915mhz.

Let’s start off with the Rx mode. Left to right when looking at the board. As you can see the signal is severely distorted. I checked the signal generator into a 50 ohm load to confirm that the output is in fact a sine wave. The circuit is having a dramatic effect. 

Below is spectrum analysis of the input waveform.  Fig. 12 is the waveform.

Schematic and board layout is at the end of the posting.

Fig.11

Fig.12

Fig. 14, A is the toroid out and B in input to the toroid. Just under 200 mV in and 600mv out.

Fig. 15, A is the filter in and B is the filter out. Probes are directly on the in and out of the crystal. Bypassing the 39pf capacitors in other words.  Signal cleans up nicely.

Fig. 16 has A on the input of the transistor and B the output of the board.

 So the signal cleans up again and puts out 600mV 

Questions I have:

1, Why does the circuit distort the signals as it does in a couple of places?

2, Why the poor amplification?

It will be interesting to see what others have going on with their boards.

Ok, onto the Tx mode.

Fig. 2, the input. Note the flattening of the sine wave at the bottom. The circuit behaves much better here than the Rx circuit.

Fig. 1, Spectrum display. 

Fig.4, B is the input to the transistor and A is output. That is one messed up output.

Fig. 5, Spectrum display. Note the 2^nd harmonic.

Fig.6 bored yet?  Another shot of the transistor output

Fig. 7, B is toroid in and A is out.

Fig.8 Xtal in is A and B is xtal out.

Fig.9 is A toroid in and B is toroid out. Signal look ok and relative values as well.

Fig. 10, A transistor in and B is transistor out.

Tx mode, while it has its moments earlier in the circuit, seems to work ok once the signal is through the crystal filter.

The left side of the board is a little different in layout, but I don’t think it would be an explanation of the differences between the Rx and Tx mode signal behaviours.  Below is a copy of the layout. The board shows an IC in the centre, this is where the relay goes.

Re Learning Something All the Time

I suppose I should just open a beer and sit back and have a laugh at myself, but I haven't convinced myself yet that its all that funny.  So a coffee will have to do while I contemplate a waste of about 5 hours.

I was working on 1 of 3 booster amp boards I've previously built for the Lets Build Something project.  There was a modification to be done which involved cutting a trace and putting in a jumper.  Basically it rerouted  a resistor and capacitor that was loading down the collector of the transistor rendering the circuit inoperable. Fortunately Ken, VA3ABN found the problem and reported his findings.  What makes this even more interesting is Franks circuit works without making any changes.

Where my day begins is testing the board as is before making the modification.  Somewhere along the line of soldering on last minute connectors and cables, I forgot about the mod and went about testing the board after those final touches. Of course the circuit didn't work and I even thought I let the smoke out of the smt transistor I was using.  I'm sure that only pushed the mod even further out of mind.  So after removing a solder bridge, thought I found the problem #1, re tested the board, no luck.  Testing the pot revealed a problem and eventually had to re-solder that component, thought I found the problem #2.  No luck again and this time testing proved that the transistor was not turning on at all. Replaced that smd with another one, thought I found the problem#3. No luck.  By this time I'm questioning my abilities as a homebrewer and double checking the schematic saw no errors.  This is a really simple circuit, 1 transistor amplifier, what could go wrong?  Well lets put in a through hole 2N3904 transistor and that should work as the 2nd smd transistor was not turning on either. Thought I found the problem #4. Nope not that either. If I can't make a 1 transistor amplifier work, then maybe I should give up and take up knitting. Or in the end, go get the original artical, make a coffee, get some left over Halloween candy, sit down and read up on the circuit.  I must be missing something.

A funny thing happen on the way back down the shack, arms full of crap, I realized what the problem was, I didn't complete Ken's mod. No wonder the board didn't work. Cut the trace, added the jumper, circuit works.  Not sure yet the details on how well it works, but happy that I now can see an signal on the output.

Trace cut circled in black and jumper beside it.

Coffee tastes better now.  I think I'll go work on my tower for a change of pace.

73, Peter