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

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