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Type: Posts; User: neazoi

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  1. Closed: How does single signal reception work in this transceiver?

    Hi I have designed this transceiver which is capable of upper sideband (USB) detection whereas keeping the LSB in AM mode and attenuated. So sort of single signal reception.
    This works like a charm,...
  2. Closed: Re: Grid leak VS Diode detection in regen set, advantages disadvantages

    Here are some changes I did on the third circuit to hopefully operate on a low voltage.

    1. Instead of using a variometer for L2/L3, use static coils and connect a shunt variable capacitor in order...
  3. Closed: Re: Grid leak VS Diode detection in regen set, advantages disadvantages

    How about the third link I posted? He seems to know what he is doing. I consider the circuits in figure 6 and 7
  4. Closed: Grid leak VS Diode detection in regen set, advantages disadvantages

    Hi, I consider building a small tube regenerative set and try some things out for experimentation.

    I have found two detection techniques.
    The first uses the "grid-leak" and this is common in most...
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    Closed: Replacing AT45DB081B with SST25VF080B

    Hi, in my project http://qrp.gr/cb2/hardware/schematic.gif I want to replace the AT45DB081B with SST25VF080B which is available in DIP.
    http://qrp.gr/cb2/manual/index.html (reference manual, see...
  6. Closed: Regenerative receiver based on my franklin oscillator

    In my page I have designed this franklin oscillator http://qrp.gr/minivfo/
    Now I want to investigate it's conversion to a regenerative receiver.

    As far as I can understand, I need to limit the...
  7. Closed: Re: Key switches in vintage PC keyboard. Toxic or not?

    In the beginning I thought the conductive area of the film was touching the PCB pads. Thank god I read about how capacitive switches work on wiki. These film disks are soldered on the "foamy"...
  8. Closed: Re: Key switches in vintage PC keyboard. Toxic or not?

    Get rid of an XT keyboard? That is collective :)

    Well, I measured these films with a continuity meter. The surface of the film that touches the pads on the PCB is non-conductive! The metal must be...
  9. Closed: Key switches in vintage PC keyboard. Toxic or not?

    Hi I have a vintage PC-XT keyboard, the model Keytronic KB5151 pro series. The manual of the jr model is attached, which I suppose is the same.
    The manual writes:

    Capacitive key switches are used...
  10. Closed: Re: Tube filaments on 230v? What do I need to know?

    It is intended as a lightweight and cheap CW transmitter. Since I already have these tubes... But I was thinking of completely isolate the chassis from the circuit anyway (chassis floating) because I...
  11. Closed: Re: Tube filaments on 230v? What do I need to know?

    Since they are in series, it wouldn't matter would it? Because the voltage at the ends of each filament is 45-50v anyway. This is what I am talking about.
    Maybe it's a good idea to do what Brian...
  12. Closed: Re: Tube filaments on 230v? What do I need to know?

    These are U type tubes.
  13. Closed: Re: Tube filaments on 230v? What do I need to know?

    Sorry I did not understand well what you are saying. I am not going to connect anything to the chassis. A thermistor in series with the 5 tubes. You worry for isolation because the thermistor...
  14. Closed: Re: Tube filaments on 230v? What do I need to know?

    How about if I use a thermistor and all 5 tubes? (4 x UL84 + 1 x UCL82). Their filament voltages add for 230v but I guess it is ok to run a bit lower. So can I use a thermistor in place and of what...
  15. Closed: Re: TTL to AF tone and AF tone to TTL conversion. Ideas, suggestions

    Of course. And it takes lot of trial and error practically. However because of the ASK, I tend not to think of frequency here. Even if this tone frequency is not stable enough and even if it is full...
  16. Closed: Re: TTL to AF tone and AF tone to TTL conversion. Ideas, suggestions

    Thanks Brian that is very useful to know!
    What if I did not use a capacitor in the detector, but drive the transistor base directly with a diode? This should be fast and detect only the positive...
  17. Closed: TTL to AF tone and AF tone to TTL conversion. Ideas, suggestions

    Hi, I have a kind of special requirement. I want two MCUs with serial (TTL) ports to communicate each other over a channel that accepts only audio signals, like the telephone or a ham radio...
  18. Closed: Re: Convert RS232 to UART and vice versa (discrete)

    There may be several reasons, and of different consideration for each hobbyist.
    Cost, availability and obsolescence may be some, but to my view availability is a main issue. You just may not happen...
  19. Closed: Re: Convert RS232 to UART and vice versa (discrete)

    Well I finally took the signals directly from the chip pins http://qrp.gr/cb2/hardware/schematic_simple.gif and it worked!
    The author of the firmware has included an RS232/TTL setting in the...
  20. Closed: Re: Tube filaments on 230v? What do I need to know?

    Ok so for 3x ul84 and 1x ucl82 this will be
    3x45 + 50 = 185v
    230 - 185 = 45v
    45v/0.1A = 450

    So the power resistor in series with the filaments should be 450 ohms?
  21. Closed: Re: Convert RS232 to UART and vice versa (discrete)

    I will draw a small schematic just to make sure I have understood that correctly. In the mean time, I am thinking that the MCU outputs a TTL actually isn't it? So can I just bypass the negative...
  22. Closed: Convert RS232 to UART and vice versa (discrete)

    I have this circuit http://qrp.gr/cb2/hardware/schematic_simple.gif and I need to make it communicate with this http://qrp.gr/cb2/modem/modem3.gif
    But the modem IC uses UART 0/5v. I do not want to...
  23. Closed: Re: Tube filaments on 230v? What do I need to know?

    I could reduce the number of tubes, which will require 185v for the filaments, and use a power resistor for the rest of the voltage drop. What current and value resistor should I use for the purpose?
  24. Closed: Re: Tube filaments on 230v? What do I need to know?

    I remember old television sets tubes filaments glowed brightly when the tv was switched on. Then they shut off and after a few seconds went red glow (normal operation). This is the case in almost all...
  25. Closed: Re: TCM3105 what happens if data is sent at a higher rate?

    So can I leave the settings of the tcm3105 at 1200/1200 and just send ttl data at lower speeds?
    But not the other way round, right?
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