857D for 2m weak signal work / digi modes

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KO4LZ, Jun 26, 2020.

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  1. KO4LZ

    KO4LZ XML Subscriber QRZ Page

    Anyone else using a Yaesu 857D for 2m weak signal work, especially for MSK144 or FT8? I've used this rig successfully on 6 meters, but seem to be having some issues on 2 meters, mostly on receive.

    I know 2m is different from 6 m, and I have checked my timing /frequency cal / audio levels / RF spectrum / noise, etc. etc. ;) I can receive and decode signals properly, but it seems I am often heard more often than I hear, which is a bit puzzling when I'm only using 50W and an indoor antenna (compared to "big gun" stations).

    I'm curious to hear from anyone who is actually using an 857D for 2m digital work: what settings are you using (e.g. DNR on/off/settings, etc.), what soundcard interface, or any other tips you may have.

    Thanks and 73,
    Paul, KO4LZ
     
  2. WA9SVD

    WA9SVD Ham Member QRZ Page

    I don't have an 857, but if your settings for FT8 work on 6 Meters, they should not require much tweaking on other bands, including 2 Meters. I'd suggest an outdoor antenna to start with; even a simple quarter wave whip shouldn't be too difficult, even with HOA's. There simply may be little 2 Meter activity (FT8 or otherwise) in your area; you might try contacting/joining a local club for help/suggestions.
     
  3. KN4ZKT

    KN4ZKT Ham Member QRZ Page

    This is most likely happening if you are running a smallish antenna, and the stations hearing you are running large antennas high in the air.

    How big is your antenna? You'll probably benefit a lot from just having an antenna outdoors, even if its only a small loop or dipole.

    I've worked out to about 100 miles on 2m FT8 with just a dipole at about 35ft, and 100 watts.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Quick test for receiver sensitivity that involves no test equipment: Unplug your 2m antenna from the rig, check the background noise level (S-meter is probably at "0" but also listen to it with the volume turned up and a speaker or headphones connected), then plug in the antenna, connecting it to the radio. Check noise level again. If it doesn't change at all, your receiver noise figure is higher than atmospheric noise levels with that antenna and as such your receiving capability will be limited by that.

    A receiving preamp would likely help in such a situation.

    Of course, bigger and "outdoor" antennas would also help -- and probably more than a preamp. But if it's impossible to improve the antenna, you might try a receiving preamp. Problem is, with a transceiver you'd need either a T/R switch preamp that can bypass itself when transmitting, or modifying the transceiver to place the preamp in the receive line only to assure you can't transmit into it.
     
    KO4LZ likes this.
  5. KO4LZ

    KO4LZ XML Subscriber QRZ Page

    Well, since I happened to have some test equipment handy .... :) 12 dB SINAD at 144.150 (FM, 3 kHz dev) was ~ -123.20 dBm.

    CMA180_Yaesu857D.JPG
     
    WD4ELG and PY2RAF like this.
  6. KO4LZ

    KO4LZ XML Subscriber QRZ Page

    I've had successful 2m QSOs at 500 miles and spots at over 1000 miles with this radio (857D with 50W out and 5el indoor yagi) so even this "modest" setup works okay on this side of the Mississippi :)

    My main question was whether the 857D's noise reduction feature actually helped or hurt for digital modes like MSK144 or FT8 (I can tell it helps with SSB and CW). The problem is that coming up with a repeatable, controllable test for decode performance specific to 2m digital modes is somwhat non-trivial ... and this is from someone who has a vector signal generator (SMA200A) and spectrum/signal analyzer (FSW44) in his shack. Measuring "standard" receiver parameters (like sensitivity, see above post) is very easy for me to do.

    I can create an MSK144 signal using MATLAB and/or make a "clean" IQ recording of an MSK144 signal and use those to test decode performance, but before I went that route I was wondering if anyone had experience with the effect of the 857D's NR, et al on 2m digi mode signals.

    Thanks and 73, Paul KO4LZ
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That's not particularly sensitive.

    Did you try the "noise level increase with antenna connected" test (which must be done on CW/SSB, not on FM)?

    That's more revealing. If the noise level increases with the antenna connected, you have all the sensitivity you can use; if it does not...you don't.
     
    WA9SVD likes this.
  8. KN4ZKT

    KN4ZKT Ham Member QRZ Page

    Right, but was this during an opening? I'm mainly referring to dead band conditions.

    I actually decoded you on 2m FT8 the other day, but I don't think you heard me responding :)
     
  9. KO4LZ

    KO4LZ XML Subscriber QRZ Page

    Sorry, but you'd have to define what you mean by "opening" and "dead band" By my definition, no one is making any QSOs on a "dead band" regardless of antenna, transmit power, or mode.

    I had a 542 mile contact just this morning on 2 meters. Yesterday I had four weak signal QSOs on 2 meters, including one exactly 999 miles away. The others were only 526, 297, and 206 miles. Which ones of these were due to "openings"? Does one need an "opening" for any 2 meter weak signal contacts, or can one just QRO and make contacts anytime, anywhere?

    Maybe you should try an indoor antenna :)
     
  10. KO4LZ

    KO4LZ XML Subscriber QRZ Page

    Well, according to Yaesu that's actually better than spec (-123 dBm = 0.16 μV, spec is 0.2 μV, or -121 dBm).

    Even my 9700 is spec'ed at "Less than 0.18 μV" (no idea how much "less" it is ... will measure later).
     
    PY2RAF likes this.

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