Aerocom Atom aircraft HF transmitter

Discussion in 'Amplitude Modulation' started by SM0GLD, Apr 2, 2019.

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  1. KB3OUK

    KB3OUK Ham Member QRZ Page

    3 6146s mod by a pair is probably conservatively running about 90 watts carrier. If the components could handle it you might be able to get 120-150 watts carrier from it, that tube lineup makes it pretty much a mini auto-tuning Johnson Valiant.
    SM0GLD and AC0OB like this.
  2. SM0GLD

    SM0GLD Ham Member QRZ Page

    I fund the Johnson Valiant schematic and it seams quite similar to the Aerocom tx.
    TX tubes: 1x 5654, 1x 5686 and 3x 6146.
    Modulator: 1x 5749, 1x 5726 and 2x 6146.
    Just as in the Valiant the modulator uses inter stage transformer.
  3. SM0AOM

    SM0AOM Ham Member QRZ Page

    I believe that this transmitter is similar to the transmitter half of the Collins 18S-4, which was
    about 100 W carrier output "on a sunny day". However, its smaller size would put it in the 60-70 W carrier category.

    The current draw of 5 A at 28V would barely suffice to power the filaments and control circuits of the transmitter in idle. A more realistic current draw would be in the order of 20-25 A.

    I am somewhat curious of the provenance of the unit.
    It is mid-50s, so it was sold and installed after the major shift from HF to VHF for domestic ATC.

    Also, the aircraft that were using such equipment could not be either too small, or too large, ruling out general aviation on one end, and larger air transport such as the DC-3 , Ju-52 or DC-6 at the other end.
    They mostly used Collins or SRT avionics for international flying and oceanic ATC.

    This would point to the Lockheed Electra or Lodestar class of smaller twin-engine air transport, that were around in the Nordic countries for charter flights and newspaper deliveries.

    A check with the avionics people at the Arlanda Historic Aircraft collection, where at least one Lockheed Electra Jr is preserved may give some pointers.

    KD2ACO likes this.
  4. SM0GLD

    SM0GLD Ham Member QRZ Page

    Hi K-A
    A transport plane landed at Bromma airport in the mid 70s. The radio was taken out for repair but was never reinstalled.
    Later the flight company went bankrupt and the radio was forgotten for many years. The plane was parked at Bromma Airport for a long time.
    I know the repairman and there is no schematics to be found.

    Yes I believe so. The genemotor is labelled 20amp.

    The hole thing is not very complicated but i suspect there is a few things missing.
    Perhaps I have to draw my own schematic.
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    The equipment can be dated to the mid-50s, both due to the use of the 6146, and due to the ARINC 400 "form-factor" which was introduced at this time.

    A major obstacle when dealing with ARINC packaged equipment may be to find the mounting racks and the mating connectors.

    If the bankrupt airline can be identified, the aircraft type may be located.

  6. W0KPX

    W0KPX Ham Member QRZ Page

    There is a Convair 440 sitting on the south side of the field at Bromma visible on Google maps. Could this be the aircraft this transmitter came from?
  7. SM0AOM

    SM0AOM Ham Member QRZ Page

    This is the written-off airframe of ex-Linjeflyg SE-CCX which has been parked there since the late 70s.

    I very much doubt that the Linjeflyg Convairs ever carried HF, as they flew only domestic routes, and were operational during the period when VHF ATC communications had become fully implemented in domestic airspace.

    The description fits in on the Airtaco or Transair Lockheed twin-engine small transport planes.

  8. SM0GLD

    SM0GLD Ham Member QRZ Page

    Although very interesting, but I dont think finding the airplane can get me closer to the schematics.
  9. SM0AOM

    SM0AOM Ham Member QRZ Page

    You may contact Sten, SM7WT, who worked in the avionics business at Transair for a long time.

    He could know something about this type of equipment.

    SM0GLD likes this.
  10. N0WEK

    N0WEK Ham Member QRZ Page

    Updating an old thread.

    Did you ever get that transmitter running?

    I've got just the power/modulator box for a similar rig but this one runs off of 28 volt and 115 volt 400 Hz power. The 400 Hz stuff doesn't have much of a use but I figured I'd save the audio section with the pair of 6146s and the mod transformer.

    I haven't found any other info on these.

    Greg N0WEK

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