Help with QRP Notebook SSB Phasing exciter

Discussion in 'Homebrew and Kit Projects' started by KG4GUF, Jun 30, 2008.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Left-3
ad: abrind-2
ad: L-Geochron
ad: L-MFJ
  1. KG4GUF

    KG4GUF Ham Member QRZ Page

    I think I've finally found what QRP transceiver I want to build (see: Altoids can SSB transceiver). However, I am unsure of some of the specifics. Like I mentioned in the other thread, I can handle the electronics/building part just fine and dandy, but it's the specifics of an RF system that I am still unfamiliar with.
    The specific circuit I was thinking about building is mentioned on pages 163-165 and the schematic is Fig 6-7 on page 164 of the QRP Notebook. I understand the basics of the system, but somethings still elude me.

    What is the SIG IN point located in the upperleft of the schematic? I would initially guess that this is where the audio comes in, however, I can clearly see the Audio amp down in the bottom left with a point going to a MIC AMP.

    Another question I have on this is how would I know what frequency the VFO is tuned to?

    Also, would I need a separate receiver, or would this work as receiver when i am not transmitting?

    That's all I have right now, any help is greatly appreciated!
  2. W1VT

    W1VT Ham Member QRZ Page

    SIG IN is the input for the VFO signal. According to Doug it should be +7dBm or 5mW.

    I've used two methods for indicating the frequency of a VFO. The most common is to make a mechanical dial with markings out of pen or pencil to indicate the frequency. The second is to make a frequency counter and actually count the frequency. Actually, if I remember right, I counted a multiple of the frequency, as I used dividers to obtain the phasing. In practice, dividers are a poor solution to the phasing problem, but I didn't know that before I built the radio in the mid 1980s.

    While it is possible to use diode mixers for both transmit and receive, it often isn't worth the hassle of switching around the signal or using bidirectional amplifiers to make it happen.
  3. AB9LZ

    AB9LZ Ham Member QRZ Page

    Before you do anything, secure access to an oscilliscope, phasing exciters are much trickier to get working than regular crystal filter types.

    73 m/4
    Last edited: Jun 30, 2008
  4. K3WRV

    K3WRV Guest

    The rig is an exciter only. To make it work as a transmitter, you'll need to add a VFO and an amplifier, even to get 5 W out of it. And you will need a separate receiver and probably some switching circuits as well

    There's a 6 meter SSB transceiver in Spring, 2008 QRP Quarterly (QRPARCI.ORG) by Allison, KB1GMX, but it's mostly a concept type article rather than a howto type. You could probably scale it for other bands. But I doubt it will fit in an Altoids tin.

    There are aslo the "SoftRock RXTX" rigs by Tony Parks that should be adaptable to SSB fairly easily, but the board is about 4x4 inches, so a bit large for Altoids.
  5. N0WVA

    N0WVA Ham Member QRZ Page

    When you build the VFO, you have to make some sort of dial readout know where you are in the band.

    Ive tried, but for the life of me, could never make that circuit from QRP notebook work.

    Anyone else tried it?
  6. AB9LZ

    AB9LZ Ham Member QRZ Page

    I have, and I did, but it wasn't easy, plus It doesn't want to stay in "balance". The output looks pretty bad after a short while. It was a good experience, but not a "daily user" circuit.

    There is much more than meets the eye when homebrewing. Believe it or not, learning code and building a CW rig will be easier than building a good working SSB rig.

    73 m/4
  7. W1VT

    W1VT Ham Member QRZ Page

    A good 6M phasing rig can be a lot of fun--in the 1997 Field Day I worked mostly QRP 6M with a 4 element Yagi--not only did I make 70 contacts but I worked Jimmy, who was operating J6/W6JKV! :D
  8. AB8RO

    AB8RO Ham Member QRZ Page

    I'm curious, where do you suspect that the instability was coming from?

    Man, you can say that again. I'm having a lot of fun but I'm sure not doing much operating :)

    Yep, but DSB is a much better choice for just getting something working.

    What approach do you use for building filters? I have a whole bunch of 11.998 Mhz crystals that I'd like to design a Cohn filter around but I have no idea what the motional parameters of the crystals are as they were surplus.
    Last edited: Jul 2, 2008
  9. AB8RO

    AB8RO Ham Member QRZ Page
  10. KG4GUF

    KG4GUF Ham Member QRZ Page

    Thanks guys for the answers. I'm still going to try something, it may not be as spectacular as an SSB homebrew rig, but atleast I can get started somewhere right?
    Thanks for everyone's help!
Thread Status:
Not open for further replies.

Share This Page

ad: hrd-2