Noise figures for VHF/UHF rigs... what is typical?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K3RW, Oct 23, 2019.

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  1. KN4ZKT

    KN4ZKT Ham Member QRZ Page

    Why not consider adding a band pass filter for 2m and 70cm?
     
  2. HB9PJT

    HB9PJT Ham Member QRZ Page

    Rob Sherwood's tabel does also show some VHF/UHF rigs and there sensitvity http://www.sherweng.com/table.html

    I wouldn't look at IC-910 or iC-821 because they have a very bad VFO and their transmit signal rushes all over the band and other OM are disturbed by it. I would use a mast preamplifier at the antenna if the low attenuation coax cable is more than 10 or 20 m long. This allows you to compensate for cable losses and optimize the sensitivity or noise figure of the receiver, but at the expense of the large signal behaviour.

    73, Peter - HB9PJT
     
  3. KN4ZKT

    KN4ZKT Ham Member QRZ Page

    Makes sense. When you mean by the expense of large signal behavior, as in your receiver being overloaded? Not sure what you mean exactly. Thanks!
     
  4. HB9PJT

    HB9PJT Ham Member QRZ Page

    If there are other powerful amateur radio stations nearby or other commercial transmitters, your receiver can be overloaded if the preamplifier is on and you are using a powerful antenna array.

    73, Peter - HB9PJT
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Also, remote (masthead) preamps must be switched out of line for transmitting, and for high powered stations (kW or more) this is a challenge. It can be done, but not cheaply.
     
  6. HB9PJT

    HB9PJT Ham Member QRZ Page

    When we did VHF and UHF contests in our club, we always had mast preamps in use and 500 to 1000 Watt. You have to pay attention to a few things, but it is not complicated. Either you need a sequencer or a radio that doesn't transmit before it outputs the PTT signal and a small interface for feeding the preamplifier. Up to 100 watts or so, you can also use the preamplifiers with HF-VOX.

    73, Peter - HB9PJT
     
  7. NQ1B

    NQ1B Ham Member QRZ Page

    I've found that rotating my 2M yagi around the horizon, I can tell when I'm pointing at Boston, about 180 miles away. There is a very noticeable increase in background noise level.

    Fortunately the noise sources in the local small town/rural area aren't bad.
     
  8. KN4ZKT

    KN4ZKT Ham Member QRZ Page

    That's interesting, are you sure it's noise from Boston? I can't hear power line noise over 1 mile at my QTH, and I have a 9 element (17ft boom) 2 element yagi.
     
  9. NQ1B

    NQ1B Ham Member QRZ Page

    Am I absolutely sure? No. But there are no significant population centers, factories, industrial zones, airports, etc. in that direction. The center of the small town where I live is in a completely different direction.

    I suppose it's possible that there's noise from power lines or something that just happens to be on the same approximate bearing as Boston.

    I'm also using a 9-element horizontal yagi.
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    180 miles is really far to be picking up wideband noise at 144 MHz.

    I'd suspect it's something else in that direction.
     

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