Mid Winter Madness (St Cloud Hamfest)

Ben (KD0JZK) and I (NG0R) went to the hamfest this morning.




I think that we got the steal of the show. We bought a bunch of bags of small &
medium sized variable capacitors. These will make excellent  tuners for some
of the simple rigs that I am building. In many cases I just need the VXO is just needed
to get the rig dialed into the proper sub band near the crystal frequency.   --
All of the parts in the picture came to a grand total of $4.00.




I also bought a log book for Jacob and one for Ben. I have using a spreadsheet printed
out to paper so far for them until we picked up the log books. At some point maybe
we will think about computer logging... but that is a LONG ways off for them. 
:-)



I also picked up Experimental Methods in RF Design. It is the informal follow-up/successor
for the 1977 Solid State Design for the Radio Amateur.  It has been on my hit
list for a couple of years but I have been unable to part with the money. Being able
to see them and compare them convinced me that it was worth the investment.



73 de NG0R

30m Oscillator (Day 4)

I am a little behind on posting so I am going to try to get caught up before I visit the work bench again.  :-)



Last night Jacob (KD0JZJ), Ben (KD0JZK), and I (NG0R) attended the W0CRC monthly
club meeting in Hutchinson, MN. Roger (K0RTR) and Roger (W0DEU) did a presentation
about NVIS antennas for 75m and also talked about simple wire antennas for camping
and out of town trips. We had some conversations about how 17m is a neat rag chew
kind of band.



Jacob and Ben got meet Devin KD0JHP who is a 12 year old ham that lives in the Hutchinson
area. It was fun to be able to get the kids together with some peers their own age.  
:-)



I like to bring some sort of in-flight project that I am working on. It is my personal
effort to show that there is more to the hobby than just the commercial appliance
approach to the hobby for those that might be interested in building stuff. (I own
several appliance rigs... but I get the most enjoyment out of the gear that I either
built myself or that I did some interesting integration with.) The hobby is different
to each person so it is fun to share some other points of view.



Thursday night & Friday over lunch I converted the 30m project from the bread
board over to a copper board. In the process I added a couple more gain stages.






I might have gotten a little crazy.




When I updated the schematic for this I was seeing some low/marginal

gain so I added to gain stages with the idea that I would tweak them on

the board so I could work out the details and measure it.






I was not happy with the power at any of the stages on the copper board. I consulted
with N0FP and we decided that I was being too conservative with Q2, Q3, and Q4 and
that I needed to let some more current flow and get some gain. Changing the collector
resistor from 470 to 220 ohms and the emitter resistor from 200 to 10 ohms really
made a big change. (I am now feeling some heat dissipation from the collector resistors
and the NPNs... they are not hot... but on the upper end of warm.)




I need to go back an re-evaluate if I need this many gain stages with this part. I
was in a hurry over lunch on Friday so I did not have time to make as many detailed
measurements as I might like.. but I am not seeing any gain in Q4.. and I am not sure
about Q3. It is possible that i might have exceeded the limits of these simple NPN
parts. I am going to measure each stage on the oscope and if needed lift the feed
to each stage and measure them on the spectrum analyzer. If I exceeded the part specs
it is possible that I am just adding harmonics in the NPN as I hit it too hard.



Depending on how things look and measure out I will likely end up moving the low pass
filter around once I figure out how many gain stages that I need during this round
of testing.



This is also making me think that I need to build a simple test fixture and use the
signal generator to test one or two stages and see where the upper limits of the part
are.



I would like to sneak in a little bit of bench time Saturday night or Sunday morning.
This weekend is pretty busy with events and chores so bench time will be pretty limited.



73 de NG0R

PCB Etching

I just saw some good info on PCB etch for the homebrew
folks and thought that it was worth putting up on the blog.



http://www.pulsarprofx.com/PCBfx/main_site/pages/start_here/index.html

 

A nice site that
discusses how to do this and where to get the stuff. There has been quite a bit of
chatter about using laminating stations for the thermal transfer.

 

Search for "GBC
laminator" on eBay and you should find it.



The rumor is that the GBC laminator is good for .032 boards with one pass through
the heater. I will need to order some transfer paper and some etchant. I am enjoying
making boards at home with pads and islands but some days I would also like to have
the sharp/clean/dense boards that you can get when you lay them out in software and
then use the laser printer.

Island Construction

Tonight I started to layout a board for my 30m transmitter project.








I updated my schematic to include a couple more gain stages. I then grabbed a piece
of copper circuit board and started to map out where the parts were going to go. I
left room for a bracket and BNC on one edge and then on another edge I left room for
a variable cap & bracket + something to hold a 1/8" or RCA jack for the CW key.



I drew it out in pencil and then used a Sharpie marker to make the notes more readable
once I felt ok with the parts placement. I borrowed a Dremel drill press from N0FP
earlier this afternoon. I used a NJ pad cutter to make the isolated islands on the
board. (A few extra RPMs are your friend with the dremel & press so that cutter
does not try to walk or jump around. I figured this out about 12 pads into the project.)
Once the islands were cut I tinned the islands to make them easier to work with.



Since this is a learning experience I am trying to leave room incorporate changes
as I come across them. (Gain & filtering are likely additions.) I am looking forward
to morphing the breadboard into a copper board with solder connections and then hooking
it up to the test gear.




The island cutter was a lot of fun. I like this as a tool to build some quick circuits.
I think that I will need to purchase a another Dremel and a matching press when the
right opportunity comes along.



73 de NG0R



PS...  Someone asked for more info on how this works



I bought the tool from:

http://www.njqrp.org/islanderpadcutter/index.html




Here is an illustration of how it works:




(illustrations shown above, and liberally used in the instruction sheets
shipped with the pad cutters, were graciously supplied by master graphic artist Paul
Harden, NA5N)




The NJQRP no longer sells these kits. (I have three of them.)





You can buy a similar version from Dan's Small Parts:

http://www.danssmallpartsandkits.net/






http://www.danscloseoutsandspecialdeals.com/Dansspecialdealsno3.html







Be aware that Dan's cutter is designed to fit into a drill press... not a Dremel.

Java Circuit Simulator

This is pretty cool:   http://www.falstad.com/circuit/









While this is not a detailed as something like LTSpice (which is very cool) this is
very useful. While I am not sure if I can get it to simulate HF/VHF frequencies there
a lot things that you can simulate at lower frequencies.  You can run this within
your browser if don't want to save it locally.



You can draw out a schematic from scratch or use some of the existing template circuits.



PS... Updated post....


Paul sent me a response this morning to a question about how to scale this into the
HF frequency range.



I am tweaking a simple NPN Common-Emitter follower circuit shown below.




(yes... I know that the picture says 10.1mHz instead of 10.1MHz...
I figured it out after I grabbed the image.)




Go the menu and select options.... other options.

You should see the window below. I changed my "time step size" to 100p. (10p might
give a nicer sine wave depending on what you are looking at.)






Next I edited the value for the signal source. I changed it to: 10.138MHz which will
show up as 10.1MHz




Very cool stuff. I will have to play with the later. It might be an interesting way
to look at Class A vs AB vs B vs C amplifiers in quick fashion. (I don't use LTSpice
enough to quick in setting up simulations especially between AC & DC analysis.)

30m Oscillator (night 4)

I made a few changes tonight and feel pretty positive about the limited time that I had to work on it.






Today's notes:

• 
  I removed the tank circuit and replaced it with a resistor on the collector of Q1.
  (The oscillator should now be a wide band design for future projects.)
  
  


• 
  I re-biased Q2. (This morning before work I built a spreadsheet that helped me better
  understand the values of the components and the impact on the transistor.)


• 
  The loudest harmonics are now about 42dBm down. (The two loudest are the 6th &
  7th harmonics.)


• 
  The power at the output of the filter is about -10 dBm or .1mW


• 
  I updated the schematic with the changes.
  
  

Next steps:

• 
  Move this to a copper board with islands or Manhattan pads


• 
  Design an additional gain stage (or two)
  
  


• 
  Research "class AB" and "class C" amp options
  
  

30m Oscillator - almost a transmitter (night 3)

I finally got back
to the bench a week after after my last visit to the breadboard.



Don't even ask how I got to the bias values for Q2 as I tried so many
different things tonight that I am not even sure... this what the board had when I
unplugged it and called it a night.




Positive news:

• 
  I
  figured out the issue with the filter and the harmonics not being rejected. It turned
  out that the ground side of the BNC on the breadboard was not making a good connection.
  I moved the wire to a new location to make it easier to connect some test probes and
  that resolved it. If I was doing this Manhattan style it would not have been an issue. 
  :-)
  


• 
  The harmonics are down
  18db without the filter and 52db with the filter. The filter is providing 34db of
  suppression which is almost exactly what the model suggests that it should do.
  


• 
  If were going to put
  this on the air it would be legal. I think that the harmonics need to be down 43db
  and I am beating that with the low pass filter + tank circuit.
  

Less than positive
news:

• 
  I am not getting jack
  for gain from Q2 at the moment. I can't really measure power very well since I don't
  have a RF power meter in this power range. (I am working on that via eBay.)
  I went to the oscope and measured the base and collector of Q2 on channels A &
  B and it suggests that I am seeing about +25mV of gain peak to peak.
  

A bonus:

• 
  I
  was able to make it into a VXO!  -----Since it was pretty
  stable I decided to grab a variable cap from the one of the junk boxes under the bench.
  I connected it from the Q1 emitter (before the Q1e to R4 connection) and the
  other side to ground.  Sure enough I can swing the frequency.  I can move
  it from 10,138,400 to 10,170,000.   At 10.170 the cap measured about 150pF. 
  If I was really going to do something like this I would put it on the board (without
  long alligator leads) and remove the tank circuit on the collector. The variable cap
  impacts the tuning on the tank circuit and also pulls down the power output by
  10-15db in the current configuration.
  

Next steps:

• 
  I need to understand
  how to calculate gain related to the bias of the transistor. There are so
  many ways to approach this and they all have nuances.
  


• 
  I should remove the tank
  circuit to make it an all band oscillator. (With the low pass filter and the amount
  of feedback the tank is probably not needed.)
  


• 
  I should run the low
  pass filter model and come up with values that could be substituted depending on what
  band you want to use within the 5 pole design.
  


• 
  I have bunch of trimmer
  caps on order... it might be fun to make the cap part of the circuit so that I can
  tune this into the QRSS sub band.
  


• 
  I need to determine how
  to key this so that it could be used a transmitter at some point down the road.
  


• 
  Eventually I should move
  this to a copper board with islands or Manhattan pads to improve the stability as
  a test fixture. 
  

2 hours
of bench and documentation time is about as good as it gets at the NG0R QTH.

2010 MNQP - It's in the log

Ben (KD0JZK) and I (NG0R) operated the Minnesota QSO Party today.



We got on the air around 10:30am. (I had to take Joe to basketball this AM prior to
being able to play radio.) I figure that we probably spent about 3-3.5 hours on the
air. Ben had a pretty nice pile-up on 20m SSB for about 60 minutes to start the contest. 
After lunch he operated for little while and then took a break to visit the XBOX.
I picked up some county and state multipliers on CW search & pounce style during
his break. About the time that we were going to wrap up we had another quick run on
40m SSB to end the radio event.








The score is pretty modest. I was pretty happy with the fact that all of the SSB contacts
we completed by Ben while I did the logging. This is first real exposure to trying
to run a pile-up. (Ben is 9 years old.) A kid's voices is like adding 10db to the
strength of your signal.






We decided to call the event around 2:30p as we had a project for school that we needed
to work on that involved a small road trip and some time on a friend's lathe.



It was a fun way to burn a few hours generating RF.



73 de NG0R

End Fed Half Wave Antenna Tuner

Here is a neat little project that I keep seeing pop up. --EFHWA



At some point this season I would like to build one or two of these. They would make
a nice addition to some of summer camping trips and visits out of town to visit friends
and relatives. I have always wanted a simple station that I can take on the road.
Maybe something like this and KX1 or a Rockmite might be the ticket.



http://www.swlink.net/~w5jh/efhwa_at.htm









I probably have all of the parts sitting on the workbench and in the parts bins. This
might be a fun weekend project with Jacob KD0JZJ and/or Ben KD0JZK. The kids might
enjoy making a contact with a wire antenna.





PS... A follow-up note to the original post....

Scott N0AR suggested visiting the following site:

http://www.aa5tb.com/




I had forgotten about the AA5TB site... it has a huge amount of information. A great
place to geek out about EFHWA ideas.

Serial Ports for Linux and XP-VirtualBox

I have a nice Linux dual core PC in my shack that I use for most of my radio activities. I need the ability to run Writelog for a radio contest this weekend. (My son wants to operate the Minnesota QSO Party on Saturday from our QTH.)  I decided to install XP in a VirtualBox.



Last night I spent 4 hours trying to the serial ports to pass-thru with limited success.
In the end I decided to move the couple of ports that I need to USB. The USB pass-thru
works awesome. My XP virtual machine sees the ports as standard serial or USB depending
on what the device is.  The performance is awesome... I am really impressed at
how response the XP session is. I reconfigured my general purpose logging program
(CQRLOG.... it ROCKS!) so that it uses the USB ports as well.



Ideally I would like to find a Linux based software solution for contesting. I suspect
that it is do-able once I do some more research. (I did try the MNQP logger and Writelog
under WINE with very limited success.)



Here is my device mapping:



Linux Native


/dev/ttyS0 = PSK Warbler

/dev/ttyS1 = former port for Rigblaster Pro


/dev/ttyS2 = former port for IC-756 CIV


/dev/ttyS3 = Elecraft K2

/dev/ttyUSB0 = K1EL Keyer

/dev/ttyUSB1 = Rigblaster Pro

/dev/ttyUSB2 = IC-756



Linux-->XP Virtual Machine


/dev/ttyUSB1 = Rigblaster Pro (Com1)

/dev/ttyUSB2 = IC-756 (Com2)

/dev/ttyUSB0 = K1EL Keyer (Com3)