开云体育

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

Gang, 1. First of all you are going to need something like the following RF probe to measure the output of the f_T tester we have been discussing in previous posts. There are a lot of RF probes that use the one diode, a 4.7M resistor and .... For this project I wanted more sensitivity. RF probe <https://tinyurl.com/yh2estzc> The reason for this is that I find that with the Rigol scope there is some jitter on the max values of the output from the CAL and OUTPUT. I am going to use the probe and an analog VTVM, B+K Model 177 VTVM, for a more steady reading. This meter I found at a swapmeet for $20 USD and I refurbished to like new. Big meter. 2. You will need the f_T fixture found at f_T fixture <https://techlib.com/newprojects.htm> Copyright by Charles Wenzel. No call sign that I see. This will now allow you to check all your transistor stock, old and new (see below), and document your builds. Call it f_T#1 by CW for your measurements using the original unmodified version. Now make your measurements according to the instructions in the schematic. V_in=1.0V_pk or 0.707V_RMS. Whatever voltage you get a CAL, and it may not be 100mV, make that the voltage out, V_OUT, to increase f_input to match. Then multiply the f_in by 20 to get f_T. Easy as pie. They just need to match. The value is not critical. 3. [Advanced] Now, Steve, AA7U, and I have mods to the fixture. Simple. Change the 150ohm resistor from V_cc to the 1K and 82ohm node to a variable resistor. I used a 2K and Steve uses a 500 ohm variable. The 500 will work better, but I didn't have one. Use this variable to adjust the bias to get 10mA through the 100ohm emitter resistor for the transistor you are testing. Since Steve and I are doing measurements for the V_ce in the spec sheet, we have a variable lab supply for the 5V source and we vary it to get the V_ce in the datasheet and adjust the variable R to get 10mA. You measure V_c, the collector voltage to ground, subtract 1.0V to get V_ce. This is going to be like adjusting a regen receiver. Also, use a SPDT switch and just switch V_CAL and V_OUT to your voltage measurement scope or meter so you won't be moving leads back and forth. Idea from Steve, AA7U. Speeds things up. 4. Cheap transistors. <https://www.aliexpress.us/item/3256805183310544.html> I have the 1,000 2N3904 NPN transistors received yesterday. Using the f_T#1 configuration, so that you can compare your 2N3904s to these, here is what I get. The cost was $14.64 USD from the site. He has about 50,000,000 left, so rush and get yours before they run out. There are some other transistors there and 1,000x2N7000 JFETs for $23.89+$7.94S&H. Now I did the following measurements as a first pass test to determine how critical the V_ce voltage is to the resulting f_T. It does matter. Also, I'm using the Rigol scope, so mileage may vary until I can get round to it using the diode probe and eliminate the small jitter. V_cc replaces the 5V supply in the schematic. V_c is voltage from the collector of the DUT to ground. V_ce is 1.0V subtracted from V_c, since there is a 1.0V drop across the 100 ohm emitter resistor due to 10.0mA current through it. V_cc I_C V_c V_ce f_T 5.25V 10.0mA 1.58V 0.58V ---- couldn't get a match V_OUT too low 9.00V 10.0mA 5.42V 4.42V 104MHz 12.0V 10.0mA 8.44V 7.44V 142MHz 23.6V 10.0mA 21.00V 20.0V 176MHz h_FE=331 as measured on the Chinese Critter Checker h_FE between 100 min and 300 max on Philips Semiconductor datasheet at I_C=10.0mA. Don't know what the emitter current is in the tester, not sure it's a valid comparison. f_T is shown to be 300MHz minimum in the datasheet. Because the h_FE=331 value, I'd expect the f_T value to be lower, but by how much is a guess. At f_T=176MHz, the transistors should be good enough for up to 0.1*f_T or so, but that is to be determined. For smaller quantities and better quality, you may want to shop around. I'm just pointing out how cheap these things were and I have a large number of projects to experiment using them in. It would be a waste to not use them up. They came in 12 days from the order date. These are

Nice piece this morning on NPR regarding Digi-Key. https://www.npr.org/2025/04/24/nx-s1-5332209/digikey-tariff-small-minnesota-town-big-company I didn't know it was started by a ham (AE5E) Jerry KI4IO Warrenton, VA

Looking through my library, this is the earliest example of using PCB pads glued to a board for construction. Is it the earliest you have seen? September 1979 QST (back when there were construction articles) "Quick and Easy Circuit Boards for the Beginner" by Doug DeMaw, W1FB <sk>. Page 30-34 of the "QRP Classics" book by the ARRL dated 1990. FYI -- chuck adams, aa7fo QRP WAS 17m started Apr 2, 2025 WAS-17 QRP --> TX,FL,SC,GA,OK,AR,KS,AL,AZ,MN PA,CA,CO,WI,NE,ID,IL,NC DXCC W,VE,JA,PY

Not a direct answer to your question, but ... yes, LTspice can be tough but probably no more than any other true SPICE package. I've presenting an introductory talk on the subject at FDIM. I'm not a super "power user" though. If you have an .asc file that's giving you problems, you can email it to me (include any models not part of the program) and I'll see if I can figure it out. Sometimes a second set of eyes can find a problem. 73 Nick, WA5BDU

I bought a no name LC100a on aliexpress figuring it was worth the risk as they offered free returns. Unless I am really missing something, it looks like I will be taking them up on the free return. I understand my testing method is awful. 5% caps using one cheap device to compare to another cheap device should make most cringe but the Kaiweets meter is usually good. Those are 330pf caps. I have some 1% ones I should dig out but at this point I doubt it will matter. I did run and save all the self calibration routines several times. This is my fault for expecting anything better for $13 from a seller called Pure Pure Grocery Store but sometimes it is fun to roll the dice. Fun fact, the price is already up $5 from 2 weeks ago. Does anyone with one of these devices know of a trick I might be missing or as I suspect is this just more garbage made with floor sweepings?

I've begun building this transmitter (Manhattan style) but cannot get the oscillator to oscillate. Has anyone built this before? I also put the oscillator into LTSpice and did not see oscillation. Does anyone know if this will work?