The first thing that I noticed was that I had my RF gain and Audio gain controls wired backwards. After I fixed that I noticed that the receiver had a real bad drift problem. I immediately asked for some help finding some new capacitors on the QRP-L mail list. Steve Smith, WB6TNL came to my rescue with some nice NP0 capacitors for C2, C4, C5, C6, and C8. C8 evidently was the worst offender because as soon as I replaced that capacitor the frequency drift improved immediately! Before I replaced C8, the radio was just about useless. Now I can go make a cup of coffee and the radio is still on frequency when I get back to the shack. :)
Now I want to add some modifications to this receiver: a S-meter and a digital display. I will update my blog when those modications are complete.
Hello Alan,congrats,nice project and improvement on it,
ReplyDeletecoud you give me more details about L1 and L2 (how many turns ,wire,dimmentions) ernando@oil.com.br,tanks
Toledo,
ReplyDeleteSorry for the delay factor in replying to your question. I will also email you my answer.
L1 = T-50-2 toroid. Sec. 26 turns #26 enameled wire, pri. 1 turn #26 closewound over bottom of sec.
L2 = T-50-6 toroid. 22 turns #26
Good luck on your build of the Neophyte Receiver!
Thanks for posting this. Do you really need both switches S1A and S1B? Or should I see one of these switches as part of one of the alternative connections?
ReplyDeleteSteve, thanks for stopping by the blog. The DPDT switch is so you can turn on/off the filter circuit. If you don't need the filter you can get rid of the switch and the entire filter circuit also. Let me know if you have any more questions.
ReplyDeleteI decided to build this rig, following your schematic. It works well on SSB and CW, though I find tuning to be more critical than I'd like. My rig struggles with AM signals though as there's a great deal of heterodyning going on and it's hard to hear much else. I'm sure I'll have fun in days ahead tweaking it and trying to improve it. Thanks very much for posting this schematic. It's a great project.
ReplyDeleteI decided to build this rig, following your schematic. It works well on SSB and CW, though I find tuning to be more critical than I'd like. My rig struggles with AM signals though as there's a great deal of heterodyning going on and it's hard to hear much else. I'm sure I'll have fun in days ahead tweaking it and trying to improve it. Thanks very much for posting this schematic. It's a great project.
ReplyDeleteSteve, you are welcome! Congrats on building a working receiver. It is always fun to tweak and improve a circuit. In my opinion, that is when the real learning begins!
ReplyDeleteHi Alan, I'm so happy to find your blog about the Improved Neophyte. I'm a newbie at kit building. I ordered the PC board from FAR circuit, collected all the parts. I got it to work sorta except for the audio filter which is why I wanted to build this receiver.
ReplyDeleteThanks for the advice about using NPO caps to reduce drift...I will have to do that! But before that, I have to solve a couple issues: 1. the frequency range is near the top of 40m (7.288 to 7.3xx), how do I get it to tune lower in the 40m band...around 7.030mhz for QRP? 2. The audio filter part is oscillating, when I switch the filter on, I hear this high pitch piercing tone! I've checked all the parts in the audio filter circuit so I'm not sure what is causing the oscillation.
Also, I have trouble finding a 25pf air capacitor, does it have to be around 25pf? If i use something higher in value, what happens? Does the frequency range "scrunched" together? Thank you for your advice! Anh N7ANH
Hi Anh, it is nice to meet you! I couldn't find a 25pf air variable capacitor either so I opted for a 50pf air cap that was in my junk box. By experimentation I was able to get a tuning range of 7.000 to 7.233 MHz. I used C9 trimmer cap to adjust bottom of the band tuning (band edge set).
ReplyDeleteSet your receiver as low as it will go (7.288 MHz) and adjust C9 to get you close to 7.030 MHz or the very bottom band edge 7.000 MHz. If that doesn't work, you may have to add a turn to L2
I built another receiver in 2022 (my third version). In my first version I used a 741 op amp rather than the TL081 referenced in the original article. The filter worked great.
Please send me an email and pictures of your build. My email is oalanjones at gmail dot com
N8WQ
Thank you Alan for your advice and encouragement! I finished the Improved Neophyte and got it working! I enclosed the project in a 28oz tomato can! Thanks again es 73, N7ANH
ReplyDelete