Bridgecom repeater?

Discussion in 'Ham Radio Discussions' started by WA2NAN, Sep 20, 2019.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I agree, but using CTCSS 100% of the time and opening the squelch all the way might work.

    I don't think they tried that yet, but should.
     
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    I am under the impression that the squelch cannot be easily disabled and the minimum level that the squelch can be set requires a -122 dBm signal (about 0.2-microvolts) to open. That is an almost "full quieting" signal.

    Is there somewhere, on the Internet, that the technical manual for the repeater can be found? I would definitely like to see just how the squelch works and if it can be defeated.

    Glen, K9STH
     
  3. K7JEM

    K7JEM Ham Member QRZ Page

    .2 uV is nowhere near full quieting. At best, it is squelch threshold on a non pre-amplified reciever.
     
  4. WA6OSX

    WA6OSX Ham Member QRZ Page

    kerry, i think you're just missing that old school hysteresis squelch...
     
    WG8Z likes this.
  5. WA2NAN

    WA2NAN Ham Member QRZ Page

    I've been looking at the settings again on the Bridgecom. Receiver setting have
    1) CSQ REPEAT-not checked
    2)COS SETTINGS - VALID SIGNAL OR CARRIER
    (I'm using carrier)
    3) RX SIGNALING set to 151.4
    4)TX SIGNALING set to 151.4 (also has carrier only (CSQ) - off)
    5(TX HOLD TIME set to 3000 (ms)
    ANY COMMENTS??
    Are their any bridgecom users out there that have a good setup that works well and doesn't drop squelch on weaker signals? Please let me know...……..tnx
     
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    JEM:

    At least 20 dB quieting and, with a fair number of receivers, near full quieting especially with an "active" front end. I agree that with a passive front end, it takes at least 0.5-microvolts or more.


    NAN:

    Try the "valid signal" COS setting and see what happens.

    Glen, K9STH
     
  7. K7JEM

    K7JEM Ham Member QRZ Page

    It takes a lot of signal to get to "full quieting", it doesn't happen anywhere near 12dB SINAD or 20dB quieting. It is an easily measured parameter, all you need is a signal generator and a dBm meter, like a telephony transmission test set. Set your signal generator to 100 uV with a dead carrier. Measure the output noise from the speaker, with volume set fairly high. This might be in the range of -45 to -50dBm or so, depending on how quiet the signal generator is, etc. Then reduce the signal generator output until you see the noise start to rise. At that point, you are not longer "fully quieted". You might specify that there needs to be a 3dB increase in noise to get a hard line measurement, but in any case, this number is going to be more than a uV, in the best RX.

    12dB SINAD is a level most modern manufacturers use to specify sensitivity on mobile FM radios. This level occurs around 4dB above the RX noise floor. The noise floor is dependent on the RX bandwidth and the noise figure of the particular radio.

    On a 15KHz wide RX, the noise power is at -132dBm (at room temperature). The very best a RX could be is -128dBm for 12dB SINAD, but this assumes a RX noise figure of 0dB, which is not possible. Typical NF for FM receivers is from 5 to 10dB (sometimes more, with a passive front end).

    This means a very "hot" RX will have a 12dB SINAD of -123dBm or around .16uV. This number typically is closer to .2uV, or around -121dBm. Typically, 20dB quieting will be reached at a 3dB stronger signal than the 12dB SINAD level. If the RX is -123 at 12dB, then the 20 dB quieting point will be around -120. The "full quieting" level will be around 15 dB (or more) above the 20dB quieting point, or around -105dBm or 1.26uV of signal, maybe more.
     
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    JEM:

    I am from the 20 dB quieting era and not the 12 dB SINAD. Over the years, I have seen a fair number of receivers that achieve 20 dB quieting at the 0.2-microvolt level. The 20 dB quieting level occurs at the point where noise just starts to appear in the signal. It does not take all that much more signal level to reach full quieting.

    The original sensitivity level, to reach the 20 dB quieting point, was, with Motorola and General Electric receivers, for several decades, no more than 0.5-microvolts. Then, in the 1970s, receivers with a 0.35-microvolt signal level started becoming available. With the high band Motorola MHT series Motrac units I have seen the 20 dB quieting level reached at around 0.2-microvolts fairly common.

    Most experienced two-way radio technicians got where they could determine the 20 dB quieting point "by ear". When challenged to make the measurement "by ear" and then have the sensitivity measured using an actual meter, the difference was, with an experienced technician, within a dB or so. Basically, close enough for all practical purposes.

    To measure the 20 dB quieting point using an actual meter, a VOM, with a cupric oxide rectifier for AC measurement, was connected across the receiver audio output. With the squelch open, but no signal generator attached, the volume control was adjusted for some convenient voltage level. For example 3-volts. Then, the signal generator, with a well calibrated attenuator, was attached. Next, the signal was adjusted to where the VOM read 1/10th the reading of the initial no signal level which, with a 3-volt initial reading would be 0.3-volts. The reading, on the signal generator attenuator, then indicated the 20 dB quieting level.

    During the 1970s, when I owned the Motorola reconditioned equipment center for the south-central United States, I definitely measured several thousand of the MHT Motrac units.

    Glen, K9STH
     
  9. W4OKW

    W4OKW Ham Member QRZ Page

    Go to the Repeater Builder website and look for the SC-50 Squelch kit. This is a MICOR squelch circuit that can be added to any receiver (it uses discriminator audio which is available from the Bridgecom). Sounds like a hysteresis issue and the SC-50 will fix that.
     
    WG8Z likes this.
  10. K7JEM

    K7JEM Ham Member QRZ Page

    I agree with most of what you posted, the big thing I am pointing out is that it takes around 15dB more of signal to go from 20 dB quieting to full quieting. That is to say that you will never reach full quieting on less than a microvolt of signal, even on the very best reciever. Typically, it will take a couple of microvolts, or more, to get there.

    The definition of "full quieting" is the point where the audio signal doesn't get any quieter, even as RF signal increases. Perhaps you are using a different definition.
     

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