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Kenwood TH-D74A for satellite work?

Discussion in 'Satellite and Space Communications' started by WD9EWK, Oct 6, 2016.

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  1. 9G5AR

    9G5AR Ham Member QRZ Page

    I'm certain glad to have got them (kenwood HT's) while I could.


    My sat kit consists of the following.......

    Elk - Antenna
    FT-818 - Tx
    TH-D72 - Tx/Rx ( FM )
    TH-D74 - Rx /Recorder ( SSB )

    MFJ 916B - Diplexer /Duplexer.

    The MFJ 916b does not seem to work well (desenses the TH-d74) on mode J (v/u) sats.
    ( although it claims a 60dB isolation ).

    Has anyone tried the Comet CF-4160J ?

    Below are some pics of the internals.
    That internal shield in the comet must count for something.

    CF-4160J.png MFJ 916B.png
     
  2. WD9EWK

    WD9EWK Ham Member QRZ Page

    I have tried the Comet unit, and some from Diamond as well. I'm still happy with the MFJ-916B, even with V/U satellites. A few years ago, a comparison between the MFJ-916B and Diamond MX-72 diplexers was done, and the MFJ outperformed the Diamond unit. I also saw this review of the Comet CF-4160J you mentioned.

    As for using the TH-D74 as the downlink receiver with V/U satellites, I occasionally saw some desense, mostly when satellites are close to the horizon. I would see some of that when working FO-29 in the past. I have not tried using the TH-D74 as the downlink receiver with RS-44 yet. I think what might be happening is that RF - or that pesky third harmonic of the 2m uplink frequency - may be getting directly into the TH-D74. The TH-D74's case doesn't shield the insides as well as the case of a radio like an FT-817 or FT-818.

    In recent times, I have started using an Icom IC-R30 receiver with an FT-817 for working the SSB satellites. I think it has a slight edge over the TH-D74 for SSB reception at 2m and 70cm. Like the TH-D74, it has a built-in recording function, and the WAV files made by the IC-R30 aren't as big as the WAV files made by the TH-D74. My FT-817/IC-R30 combination did well with RS-44 a couple of weekends ago, when I was working satellites from DM31 in southern Arizona.

    Happy 2021, and 73!
     
    9G5AR likes this.
  3. 9G5AR

    9G5AR Ham Member QRZ Page

    When you do try the TH-d74 (as receiver) with RS-44, please post a summary of your observations.

    Radiomasterlist has the ff ....

    R30 receiver sensitivity (SSB/CW) : (-117dBm)
    0.25 uV (144~148 MHz, 10dB S/N)
    0.32 uV (430~450 MHz, 10dB S/N)

    TH-d74 receiver sensitivity (SSB) : (-123bBm)
    0.16 uV (144~148 MHz, 10dB S/N)
    0.16 uV (430~450 MHz, 10dB S/N)

    FT-818 receiver sensitivity (SSB) : (-125dBm)
    0.125 uV (144~148 MHz, 10dB S/N)
    0.125 uV (430~450 MHz, 10dB S/N)

    I understand that the th-d74 case may not be doing a good job of shielding, but I'd like to make the best of what I have..
    :)

    I tested my MFJ916b with a VNA and found it offers no more than 50dB isolation.
    The RS-44 Tx freq I tested ( 145.960mhz - on the low freq port ) could be heard on the high freq port / desensing it.

    With the cable to the th-d74 antenna port disconnected, I did not noticehear anything get directly into the th-d74.

    Looking forward to your experience/feedback on the TH-d74 Rx on RS-44.
    Thanks for the great suggestions.
     
    KA2CZU likes this.
  4. IU2OZH

    IU2OZH Ham Member QRZ Page

    Hi there, I'm a newbie to linear sats to please take my comment with a grain of salt, I'm still trying to learn the ropes...

    My current setup is an IC-705 on TX with a TH-D74 on RX.
    I keep my arrow antenna on the balcony of my apartment. I have only been able to complete a couple QSOs so far but it's pretty fun to try.

    Up until a few days ago I was having a hard time even finding myself but after adding the diplexer on the RX side I can now hear myself pretty often on most U/V sats (like CAS4A).
    To make things easier (or more complicated...) I'm also developing my own "doppler shift adjuster" with a raspberry pi (https://github.com/giordyb/doppler_shifter)

    I Usually I keep the radios on my desk and have some RG58 cables (about 3.6m long) going to the Arrow outside and go back and forth between the desk and the balcony to adjust the antenna as the sat moves.

    Today I tried something different: I made an extension cord for the mic and PTT (so that I can leave the 705 on the desk) and moved outside with the D74 and headphones so that I can move the antenna better. Was able to hear myself on a U/V sat this morning but when I tried RS44 every time I pressed the PTT I heard what I think is de-sense, even when lowering the power output of the 705 to 5w.
    I remember being able to use RS44 before but I was not as closed to the antenna as today.
    Any suggestions?
    Thanks and 73
     
    N4DJC likes this.
  5. N4DJC

    N4DJC Ham Member QRZ Page

    The 705 is a nice radio, even for FM if you’re not blindly calling. It tunes as fine as you want and the waterfall is very helpful if you’re not using computer control.
     
  6. WD9EWK

    WD9EWK Ham Member QRZ Page

    Sounds like the antenna and D74 need to be separated more, like you had originally.

    I saw a similar thing in the past with FO-29, 2m uplink with 70cm downlink. Once that satellite was higher in the sky, and my antenna was pointing away from the horizon, any interference from my 2m uplink went away. I haven't tried RS-44 with the D74 as the downlink receiver, but I hear what you describe with other radios as the downlink receiver (Yaesu FT-817, Icom IC-R30) if my antenna is pointing closer to the horizon than over my head.

    73.
     
  7. IU2OZH

    IU2OZH Ham Member QRZ Page

    Tried RS44 again but this time I kept the radio far from the antenna and only had a little bit of de-sense, was able to hear myself clearly on the downlink. Thank you for the tip!
     
    WD9EWK likes this.
  8. IU2OZH

    IU2OZH Ham Member QRZ Page

    The 705 is a great radio and I wish I could reverse the roles in my setup and be able to use the 705 as the RX instead of the TX.
    If only someone would make a handheld that can TX on SSB at U/V (other than the "shoulder-able" Yaesu 817/818)...
     
    N4DJC likes this.

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