Skip to main content

Taking a Break!

Are you tired of seeing me post about my rigs?

9/28/2016 ~ Some recent updates

I have often said that most of my rigs are experimenter's platforms and the Junk Box Rig stands as an example of that approach. Everyday I look at possibilities for improvement --some changes are in the negative column but many are in the positive direction. Usually I employ the concept of TFMS when "peaking and tweaking" a rig. Oh almost forgot TFMS is an old timer term for Tune For Maximum Smoke. Well in this case when I had the rig outfitted to run 700 Watts out (Yes, Virginia, that is not QRP) I found that I got a report of splatter. One of those Flex Guys saw me pop up on his 60 inch color display and he reported I was very broad and splattering over onto other frequencies.
 
He was absolutely right! If you are running QRP at one watt --there may be splatter that is hardly noticed but magnify that 700 times and you will notice that your signal is broad and spilling over the normal bandwidth. A simple adjustment of the microphone gain can cure that problem. So out comes the scope and I was indeed flat topping and lowering the gain didn't actually impact the PEP output but did immeasurably improve the signal quality and cleaned up the spectral purity. For reference purpose a 1 watt signal is 30 dBm and a 700 watt signal is  58.5 dBm. So you will hear that very large elephant in the room!

Once I reduced the microphone gain, the Flex guy was  happy and so now I was happy too! WE have a responsibility as hams to put out the cleanest signal possible! I am now ever vigilant to not let that happen again. The positive side was that my PNP audio amp was no wimp and I had a gentle reminder about flat topping and splatter.
 
Rummaging through the junk box I found a 2SC2166 on a board and swapped out the 2SC2075.  Now 5 watts out is an easy goal. I also made a change on the driver board where normally the EMRFD circuit has a 2N3904 driving a 2N3866 but in my circuit I have a 2N2222 driving a BD139. In the emitter lead of the 2N3904 (my 2N2222) there is a 22 Ohm resistor to ground. I replaced that resistor with a 200 Ohm pot. The center wiper is connected to ground and the top lead is connected to the 2N2222. This enables me to adjust the stage gain. When I drive the 100 watt intermediate amp ahead of the SB200, I have it set so the Junk Box Rig outputs 1 watt as that is about the max level input to the intermediate amp. In the TFMS QRP mode (without any amplifiers) I can adjust that pot for 5 watts output from the 2SC2166.
 
On 9/27/2016 I made a 400 mile hop to San Francisco from my QTH near Los Angeles running 1 watt out on 40 Meters. Not a lot of signal strength but readable. But I must confess that 40M QSO's to the mid-west are much better running 700 watts!
 
Recap: Beefier RF Transistor, Watch for Flat Topping, Variable RF Output, QRP QSO's.
 
73's
Pete N6QW

9/21/2016 Revised Microphone Amplifier and plot. (See Comments)

Revised Schematic to limit the frequency response.

Output Plot of the revised shematic

Here is a chance to tell me what is on your bench and if you have attempted to build any of my projects.

73's
Pete N6QW

Popular posts from this blog

March 31, 2024. Happy Easter to those who celebrate this day.

What a great day to Binge on Chocolate and experience the pain of that filling that has been leaking.  I would be in that category with the leaking filling(s) had I not just spent an amount equivalent to one of the fancy new uptown appliance box transceivers on two filling repairs. Well at least I can binge on the Chocolate bunnies without fear of pain. Regrettably everything appears to have jumped in price including the price of parts. Well not so much the parts as the shipping costs.  That notably is seen in the eBay treasures. I spotted a nice heathkit DX-20 for about $50 and the shipping was $65. Likely it is a twofer with part being a way to in effect charge a higher price by inflating the shipping and in part by increased shipping costs. Shipping with insurance across the US was about $150 for this jewel and that was three years ago. 6AM on the Left Coast ~ 20M Easter Sunday! My only hope is the cost of Chocolate Bunnies remains steady although a pound of See's Candies f...
Read more

January 26, 2024. A simple CW Transceiver/Transmitter

Cruise through the lower part of the ham bands bands and what do you hear? Well, FT-8 and CW. Often you will not hear any SSB stations yet go to the lower part of the bands, and it is a cacophony (I love that word) of bad sounding signals and some high-speed keying. Fast is not so much of the issue as is bad, run together and jerky keying. But none the less our hobby started there.    So, you could crank down your ICOM 7300 and watch the waterfall on CW or you could homebrew a radio. Actually, to do CW right you need more thought up front than you do with a SSB transceiver. Often, I will state that a CW Transceiver is much more difficult to build than a simple SSB rig. I published two articles in QRP Quarterly on CW transceivers and all I got was a yawn so maybe history will repeat itself.  Yawn!   30M CW Transceiver with RIT!   Of interest is that the LO is a Varactor tuned LC oscillator using a NE602. Look closely at the RIT circuit which is only activated on ...
Read more

August 30, 2024. A PNP 20M SSB Transceiver

Shown below is the Block Diagram for the 20M PNP SSB Transceiver steered in the  Transmit Mode . The components shown in the dotted block are relay steered so that the block module is single pass and amplifies in a single direction. The Block diagram show steered in Transmit.  Essentially the steering process works so that the IF Module input follows the Balanced Modulator on Transmit and then the input side follows the Receive Mixer on Receive. All done with some relays and a bit of RG174U coax. For those who count things in detail, this block diagram is not unlike what was used for the PSSST Transceiver which can be found on my website . Yes, a warmed over P3ST only using PNP devices. TYGNYBNT. 73's Pete N6QW
Read more