For those interested in getting a copy of Todd’s web site current as Oct 5th, go the the following address and download the 35MB pdf file,
….PLEASE DON’T POST THE URL IN PLAIN TEXT….
Todd, VE7BPO, who runs the “Pop Korn” site for homebrewers may have to discontinue the QRPHB web site (http://www.qrp.pops.net/) all together. He and the web master have been having bandwidth problems and it looks like the issues may continue for the foreseeable future. Throughput has been really bad the last few days, and today the site server simply froze up due to a lot of download requests. At present, Todd has taken the site off-line and will probably not bring it back up. Stay tuned for further developments.
My personal thanks to Todd for all these years of service and sharing with the homebrew community. On the plus side, he will have more time to devote to experiments and testing/measurements that would normally be spent on web site updates. I came across Todd’s work and site back in the late 90’s and have been a fan ever since. He and his site will be missed!
Wanted to mention what I found by comparing the molded inductor verse the use of a toroid for the RF Phase Shift.
Found that the molded inductor (molded inductor for the primary and four turns of hook-up wire for the secondary) has at least a 10 dBm loss at 7 MHz. I wound a toroid for the same component with ten turns for the primary and four turns for the secondary on a FT37-61 and had only a 2.8 dBm loss at 7 Mhz. So, using the toroid is the better choice. But, modeling this new insight with LTSpice still leaves me with some doubt. The RF level going into the Detector stage is still not up to 700mv which I think would be necessary for good sensitivity. I doubt I will continue on with this project in its present form. Still have some desire to use the LO ceramic osc and hook it up to a homebrew NE602/LM386 receiver I build a few years ago to see if that would work.
Have discovered some really interesting functions for LTSpice…things I wish I had known years ago. Still learning how to set-up sources for driving oscillators, mixers, etc and what types of analysis’s tell me what type of information. This learning has turned out to be more fun that I first imagined!
With the fourth just around the corner, I doubt I will get much done till next week. I have started to do the 30 meter mod for my KX1 and also want to do the auto tuner kit while I am in the kit building mood.
Hope everyone has a good and safe Fourth of July weekend!
Been trying to use LTSpice with the binuaral receiver project. What I have learned is I am quite stupid when it comes to modelling a stage and understanding what is going on (using LTSpice). I have pestered a very patient friend from down under and I decided this morning that I should be able to answer some of the questions I have been throwing his way.
So, for the near future, I need to get a better handle on understanding and using LTSpice … then I can go back to modelling what I am doing before snuffing solder fumes. There is enough tutorial info out there on the web about LTSpice and how to make the best use of it…and I need to learn (relearn???…now I am wondering how much of it I learned the first time) LTSpice from a homebrewers point of view and how to make it a useful tool for me.
This is rather embarrassing to admit, but it is the truth and I really want to be able to use it (LTSpice) the way others have come to use it and learn from it.
Mark, again thanks for some really important “learns learned”!
P.S. – I can now model a VXO with some success!
Well, found that a bad scope probe can be a big problem when trying to understand things…LOL. Since replacing the bad probe, I discovered that the LO is working fine, have just over a volt coming out and going to the Product Detector. The RF input section still bothers me but it seems to be working as it should. However, the RF Phase Shift inductor (molded inductor) may be a problem, so after looking at things, I am going to take Mark’s advice and try a torroid. This may help recover some gain I seem to be losing. I get a three fold gain in voltage (317mv input/922mv output) from the RF Amp…but this varies as the input signal decreases in amplitude.
I have thought about incorporating some type of feedback for the RF Amp section to help maintain the RF level from the input to the Product Detector. I can hear a signal with -50 dBm input, but any less than that and I lose all AF going to a speaker/headphone. I should be able to use half that value of input signal and still hear a signal. I am thinking after I try swapping a torroid for the molded inductor, I may switch to a single signal type detector or pop a NE602 in-place of the current front end and see what I get. Since I wouldn’t be able to hear the binuaral effect anyway (due to being deaf in one ear), I might as well move on and try other ideas.
I built a 40 meter NE602 receiver a number of years ago and it was fun and simple. I may use the LO from this project and incorporate that receiver into a single signal receiver. I want to make up one 80 meter LO and one 40 meter LO on separate PCB boards to have on the bench for future use. All in all, this has been a fun and thought provoking exercise. I need to keep a focus on little things that can affect the overall success of the project (Thanks Mark of helping me learn this!), and remember to check my measurement methods to ensure they are sound and accurate.
I will probably have one more update after this and then move on to another project involving a remote terminal for my PHSNA.
Been wrapped up in a bunch of chores/Honey-Do’s/etc and haven’t had much time to spend at the bench. Finally got back at it tonight and rechecked some measurements I did earlier on the LO and RF portion of the receiver project…and they do not match what I had recorded earlier.
Since the forecast is for rain all day tomorrow, I hope to remeasure everything and re-evaluate what I have so far and where to go from here. Since I am deaf in one ear…making a binaural receiver makes little sense. Have been thinking of changing directions with this project since the LO was the main interest when I started this whole thing. Thinking of rewiring the front end and using a NE602 to see what that produces…and spend some more time with the current product detector to better understand it.
A special thanks goes out to Mark Dunning from down-under who has pointed out some items I overlooked…and in general made me reconsider just what I am doing and where I might go with this. Its always better to have an extra pair of eyes and a second opinion to help one focus on what they are doing!
Well, the signal level loss was not as bad as I first thought…but the ability to discern AF is not what I was hoping for. With a -40 dBm input signal level, the AF (in headphones) is just barely noticeable. Actually, from -35dBm input and lower, the AF is nearly useable.
I have post the signal level loss with a -3dBm input signal level to show the loss for the RF portion of the receiver to be about -7dBm (from input to product detector).
The RF Amp is working, but I am losing a lot of the signal before it gets to the Product Detector. The RF Amp is giving at least 25 dBm of gain…but from the collector to the Product Detector I am losing almost 20 dBm…so something is amiss with the RF portion of this project.
I need to measure each section to map out the loss and then figure out why…or just call it quits for now and move on to another project. I was thinking of using a NE602 for the front end and use the output pins (5 & 6) for the input to the Product Detector. I built a DC receiver a few years ago that used the NE602 and it worked rather nicely. I found the project and wondering if I want to just “jerry-rig” up the idea to see if it works. Since I am deaf in one ear, a binaural receiver isn’t of much use to me…but i did want to play around with the crystal resonator LO and that is what got me started on this project in the first place.
Am quite happy with the LO part of the circuit and I can duplicate it for both 80 and 40 meters…so may build up a couple LO circuits to have on-hand for bench work. Nice to have a steady sig gen with only a few parts!
Have to think about all of this for a day or two and then decide what I am going to do. But that is where I am for now. I can make the receiver work…but it is about as deaf as I am and that is really no good to anyone .
Hello to Fred…glad your happy with my more frequent updates!!!
Well, wired up one stage of the AF section (which provided one earphone worth of audio). Using my sig gen I could hear and tune above and below the signal…but that is with about zero dBm of input signal. When I connected the project to a 40 meter antenna, I heard nothing!
Need to check the Input RF Preamp and see if it is working. There were enough 40 meter CW signals on the air tonight that I should have heard something. I may have to add a RF amp to the front end if everything else is working as it should.
The RF Phase Splitter is working as I can turn it all the one way and have lots of audio when using the sig gen for an input, and then when turned all the other way, have nothing. I am not going to build the second AF section until I determine what or why I cannot hear any 40 meter CW signals.
Finally made some time to work on the Binuaral Receiver today. Finished installing the parts for the RF Phase Shift and Product Detector sections and now am ready to install the LO/Product Detector interface transformer. The transformer is a trifilar wound torroid “roid”. I don’t care too much about winding them, or tinning the leads…but do like them as I can make each into a value that is needed and not have to order a particular inductor for each project.
I was checking the LO output with the DSA815-TG spectrum analyzer earlier today. Noticed that the second and third harmonics are only down about -15 to -17 dBm from the fundamental frequency. I may have to build either a LPF or BPF if this project turns into a transceiver instead of just a receiver.
Anyway, time to eat and get to Bible study (Wednesday night activity at our church), so will have to finish the install of the transformer either tonight or tomorrow after I get back from a group hike along the Waterloo Trail near here.