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Also if you notice I widened the sweep this time to include the 4th harmonic which shows up about the same level as the 2nd harmonic. I imagine the other filters show the same for the 4th harmonic. (Filter sweep included again.) Steve

I built the 30M W5USJ LPF from the chart, next. You'll notice on the chart that the input and output impedances for this filter are close to 50 ohms with little differences. My tests showed the same--45 Vpp (5W) output either way. That indicates if one can design the trap filter for close to 50 ohms, then the filter is indeed symmetrical. Too bad Chuck Carpenter is not still around so we could ask him if he noticed the impedances were the same for this filter and not as close to 50 ohms for the others. 73, Steve AA7U

We're all aware of the current FCC regs for harmonics and spurious outputs from a transmitter needing to be -43 dBc or greater below the fundamental output. Here's a 40 M LPF with the original response of the filter when the current -43 dBc wasn't in effect vs. with adding the trap capacitors across the two inductors, showing how the filter easily surpasses -43 dBc--quite a dramatic difference. (I used a 40 dB tap for these pictures.) 73, Steve AA7U

I've recently been testing a 14Mc power amp circuit, comparing several output transistors for 5 watts (45 Vpp) into a measured 50 ohm dummy load. I put a scope probe on the output and adjust for 45 Vpp with bench power supply set to 12.8 volts. I've found that a good transistor will give 5 watts out at that frequency at 12.8 volts. My reference has been a genuine 2SC5739. I adjust the input power from the function generator to give 45 Vpp output with the reference, then substitute other transistors to see how they compare. For instance the 2SC2078 is a popular transistor used in many CB radios as the final transistor. I have several genuine 2078s as pulls from old CBs (all over 10 years old) found in thrift shops. Most of them have a blown output transistor, but the few that are good I save the transistors. A good 2078 will give 46 Vpp or sometimes a little more output compared to the reference 5739. If you look on eBay there are literally hundreds of sellers of the 2078--the majority of them from China. I found a US seller offering 10 of them for a reasonable price and bought them to test. Every single one was a fake counterfeit with 30-35 Vpp output at 14Mc! When I complained, I was given a full refund. Someone sent me two 2078s to test, bought from a reputable US seller that most of us have bought from. Both of these too were fake counterfeits with 30-35 Vpp output. My last purchase of 2078s was from another US seller on eBay--his ad shows testing them on a Peak meter--he tests them for beta (gain) at the low currents any of these test meters can only test at. I corresponded with the seller, saying such a test at such low currents didn't tell much, that a real test would be for output power. He responded that he could only test the way he was showing but that previous purchasers seemed to be happy with these 2078s. I bought 5 of them to test--they finally arrived today, after 12 days! He's in Las Vegas, only a day or two mail time from me in Arizona, so for unknown reasons he appears to be very slow in shipping. I immediately tested all 5 and I'm very happy to report they all passed--3 gave 46 Vpp output, the other two 45.7 and 45.6 Vpp--exceeding the reference 5739 set for 45 Vpp. So these are the first Chinese 2SC2078s I can recommend, if you're looking for a decent RF power transistor. https://www.ebay.com/itm/286038719772 is the item and seller. Again note that you'll probably wait quite awhile to get these. (Email me privately if you want to know who the other seller of the fake ones is that I tested, I don't want to give his name out publicly since I've bought many things from him over the years and this is the first time I've seen fake counterfeit parts from him. Hopefully this particular part is the only fake part he's selling--listed as 2SC2078.) 73, Steve AA7U

There is a correction to the schematic! I left out the negative feedback resistor and cap on Q1. Corrected schematic here along with same picture of the test fixture from before (which has the feedback). If you saved the previous schematic, throw it away and save this one! Steve AA7U

Here's my latest rig (see pic below). It is a 10 Watt PEP single conversion transceiver using 6 printed circuit boards in a copper clad PCB enclosure. I've been having a lot of fun talking to my friends on 40 meters with this rig. The boards are as follows: 1. VFO board. (purple, front) This uses a raspberry pi pico. The pico has a really inexpensive debug probe you can get for $15. Debuggers make it really easy to find problems with your code. The board has an Si5351 and a 26 MHz 0.5ppm TCXO reference oscillator. I used Platformio IDE to develop the C++ code for this rig. I chose the Arduino framework in Platformio. 2. TX amp and filter board (left wall of enclosure). This board takes the output of the product detector (though a high pass filter) and amplifies it by 40dB. It has 2 stages.: a 2N3904 followed by a 2SC3357. It then filters the output with a triple-tuned bandpass filter for 40 meters. The purpose of the triple tuned bandpass filter is to filter out any spurs from the mixer before they get to the predriver and final amplifier. I thought about relay switching this band pass filter with one used in the front end board, but that would have over-complicated things and maybe introduced some paths to cause oscillation. I wanted to avoid bi-directional amplifiers as I wanted the rig to have AGC. 3. Predriver and final amplifier board (red, rear). This board takes the -9dBm output from the TX amp and filter board and amplifies it to +40dBm (10 Watts PEP). It has 2 stages. A pair of 2SC5706's followed by a pair of RD06HHF1's. If you push it you can get 12 watts PEP out of it, but I don't like running things at their limits. There is only one relay in this rig and it is on this board. The nice thing about push-pull amplifiers is that they attenuate the second harmonic significantly. The 5th order low pass filter on this board is good enough to attenuate all harmonics below the -43dBm limit. 4. Front end and crystal filter. (Green board closest to the rear and close to the pre-driver and final amplifier board). This board has a triple tuned bandpass filter before the mixer and also injects transmit audio into the mixer (which serves as the balanced modulator) during transmit. The output of the mixer is amplified using a 2SC3357 and then put through a 6dB pad before being presented to the 6 pole crystal filter. The crystal filter uses 12.288 MHz crystals. One thing to note about the 2SC3357: You can run it with 40mA of quiescent current, but you need to keep the the Vce below 12 volt absolute maximum in the datasheet. I power all the 2SC3357's in this rig with a switched 9 volt regulated supply. 5. Hycas IF amplifier board with AGC. (Green board closest to the right side of the enclosure). This is a variant of the Hycas IF amplifier featured in QST: https://www.ka7exm.net/hycas/hycas_200712_qst.pdf with some switching modifications to allow adjustable gain on transmit. 6. Product Detector/TX mixer/Audio Amplifier board. (Green board closest to the left front mounted on the bottom of the enclosure). This board contains a mixer, an NE5534 op-amp, and an LM380 audio amplifier.

Gang, I accepted the Soldersmoke DC Receiver Challenge on April 19th. Here is my 3 stage audio amplifier I finished this morning. Please join in on the fun! 73, Alan, N8WQ