SB-102 Aux Crystal

Discussion in '"Boat Anchor" & Classic Equipment' started by W8TMT, Sep 3, 2021.

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  1. W8TMT

    W8TMT Ham Member QRZ Page

    I picked up a beautiful SB-102 at the Dayton Hamfest a few years back. I've been tinkering with it on and off - new caps, replaced out of spec resistors, alignment, etc. and have it working very well except for a few quirks that remain. The transmitter is very near full output and I'm very impressed with the receiver performance. Anyway, to the chase. It has an auxiliary crystal installed stamped 5451.85 kHz which could have been used for:
    3.5475 Mhz
    7.0475 Mhz
    14.0475 Mhz
    21.0475 Mhz
    28.0475 Mhz
    I confirmed the first 3 to actually operate of the calculated frequencies.
    Does anyone know the significance of any of these frequencies? I'm curious what a previous owner could have done with this.
    Terry W8TMT
  2. N8YX

    N8YX Ham Member QRZ Page

    FT4/FT8 or PSK31, most likely.
  3. W3RU

    W3RU Ham Member QRZ Page

    Probably used for a 40 meter or 80 meter CW net of the day - back just before the incentive licensing rules took effect as these are all Extra CW frequencies now. The original user may well have been the net control station so everyone could zero beat on him with their VFOs. This frequency is relatively close to the band edge, so xtal control was probably important to the user.

    Jack W3RU
  4. N0NC

    N0NC Premium Subscriber QRZ Page

    ARRL code practice and bulletin frequencies. 47.5 kHz above the bottom of the band. Maybe used by and OBS (Official bulletin Station) some time in the past.

    73, Chuck
    N2EY and AD5HR like this.
  5. N2EY

    N2EY XML Subscriber QRZ Page

    No they aren't.

    They're all 47.5 kHz above the bottom edge of the band, not 4.75 kHz.


    Such auxiliary control could be....tricky....because the resulting frequency was only as accurate as the heterodyne crystal for the band in question.

    73 de Jim, N2EY
  6. W3RU

    W3RU Ham Member QRZ Page

    Good catch!

    Jack W3RU
  7. W8TMT

    W8TMT Ham Member QRZ Page

    Thanks, Chuck - that's gotta be it. Maybe some youngster used this rig to learn the code. I like it more than ever!

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