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Re: [BCD396XT] BCD396XT Intermediate Frequencies / image reception

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  • MCH
    Assuming a 15 kHz channel plan (correct me if you re using a 20 kHz plan): Is the problem an issue on 147.075 MHz as well? If not, can you simply lock out
    Message 1 of 10 , Aug 2, 2011
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      Assuming a 15 kHz channel plan (correct me if you're using a 20 kHz
      plan): Is the problem an issue on 147.075 MHz as well? If not, can you
      simply lock out 147.080 MHz from the search?

      You could also try the notch filter (cavity or shorted stub) tuned to
      162.400 MHz which would do two things:

      1. Get rid of one of the intermod products (which should eliminate the
      mix since it's in your receiver), and

      2. Likely increase the sensitivity of your receiver, as the 162.400 MHz
      transmitter must be pretty strong where you are located.

      If you have the problem with those two frequencies, you may have the
      same from say 162.400 and 154.770 ending up on 147.140 MHz. It's always
      a good idea to attenuate a strong RF signal near your receiver's location.

      You could also put say a Micor or MASTR II front end in line with your
      scanner, but that would likely reduce the sensitive range to a MHz or
      so. Since you have the generator, you could easily tune one of those
      front ends to the band of interest.

      I've put notch cavities on equipment located at the same site and had
      usable reception as close as 60 kHz away from the transmitter. You are
      dealing with a much easier situation.

      Joe M.

      Andy Carstarphen wrote:
      > It looks like it is mixing occurring in the front of the receiver. I set my service monitor to generate a signal on 154.740 and as soon as I placed it into GENerate mode, it duplicated the event. I turned the IF shift on for that channel but it made no difference. I was performing a 2 meter audit using the logging feature of Free Scan. I'll just have to handle that particular frequency manually.
      >
      > Thanks,
      >
      >
      > Andy Carstarphen - WY5V
      >
      >
      >> ________________________________
      >> From: MCH <mch@...>
      >> To: BCD396XT@yahoogroups.com
      >> Sent: Tuesday, August 2, 2011 7:52 PM
      >> Subject: Re: [BCD396XT] BCD396XT Intermediate Frequencies / image reception
      >>
      >>
      >>
      >> What you are describing has nothing to do with the XT - or any radio for
      >> that matter. It is classic 2A-B intermod (AKA mixing). Where it is
      >> mixing could be anything from the PA of the NOAA transmitter to a loose
      >> connection on your roof. It could also be mixing in the front end of
      >> your receiver.
      >>
      >> CTCSS will only help if the 147.080 frequency CTCSS is different than
      >> that used on 154.740 MHz. Or, you can use an RF filter (AKA cavity)
      >> which may or may not help the problem. It will help if the mix is in the
      >> front end of your receiver. It will not help is the mix is anywhere else.
      >>
      >> You would likely hear the same thing on any receiver tuned to 147.08 MHz.
      >>
      >> The only significance of 7.66 MHz is that it is the separation of the A
      >> and B transmitters, and of the A transmitter and your receive frequency.
      >>
      >> The same thing will often happen with any two transmitters where you are
      >> trying to monitor a frequency that is 2A-B MHz away.
      >>
      >> In your case:
      >>
      >> 162.400 = B
      >> 154.740 = A
      >> 147.080
      >>
      >> Joe M.
      >>
      >> ANDY - WY5V wrote:
      >>> In looking up the specifications for the scanner I find the following information:
      >>>
      >>> 1st IF: 380.7 to 380.8 MHz / 265.5 to 265.6 MHz
      >>> 2nd IF: 10.8 MHz
      >>> 3rd IF: 450 kHz
      >>>
      >>> I know that there is an IF shift feature. But before I use it, I want to know if there is anything special about 7.66 MHz. The reason I ask. I have discovered that when two particular transmitters are on the air, I hear them both on another frequency. Here are the stations involved:
      >>>
      >>> 162.400 KEC56
      >>> 154.740 KLD811
      >>> 147.080 RX only
      >>>
      >>> KEC56 is the local NWS All Hazards Radio station. So it is on the air continuously. When KLD811 keys up, I hear them both on my scanner on 147.080. Here is the arithmetic:
      >>>
      >>>
      >>> 162.400 - 154.740 = 7.66 MHz
      >>> 154.740 - 147.080 = 7.66 MHz
      >>>
      >>> So, does anyone know if there is anything special about 7.66 MHz inside the BCD396XT?
      >>>
      >>> Andy
      >>>
      >>>
      >>>
      >>> ------------------------------------
      >>>
      >>> Yahoo! Groups Links
      >>>
      >>>
      >>>
      >>>
      >>> ----------------------------------------------------------
      >>>
      >>>
      >>> No virus found in this incoming message.
      >>> Checked by AVG - www.avg.com
      >>> Version: 9.0.901 / Virus Database: 271.1.1/3806 - Release Date: 08/02/11 14:34:00
      >>>
      >>
      >>
      >>
      >
      > [Non-text portions of this message have been removed]
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
      >
    • Andy Carstarphen
      Texas currently uses a 20 KHz band plan. I will simply use a different radio to monitor that frequency for activity. Of the nearly 300 frequencies I have
      Message 2 of 10 , Aug 2, 2011
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        Texas currently uses a 20 KHz band plan. I will simply use a different radio to monitor that frequency for activity. Of the nearly 300 frequencies I have programmed in, this is the only one that has encountered the problem.


        73,

         
        Andy Carstarphen - WY5V


        >________________________________
        >From: MCH <mch@...>
        >To: BCD396XT@yahoogroups.com
        >Sent: Tuesday, August 2, 2011 11:04 PM
        >Subject: Re: [BCD396XT] BCD396XT Intermediate Frequencies / image reception
        >
        >

        >Assuming a 15 kHz channel plan (correct me if you're using a 20 kHz
        >plan): Is the problem an issue on 147.075 MHz as well? If not, can you
        >simply lock out 147.080 MHz from the search?
        >
        >You could also try the notch filter (cavity or shorted stub) tuned to
        >162.400 MHz which would do two things:
        >
        >1. Get rid of one of the intermod products (which should eliminate the
        >mix since it's in your receiver), and
        >
        >2. Likely increase the sensitivity of your receiver, as the 162.400 MHz
        >transmitter must be pretty strong where you are located.
        >
        >If you have the problem with those two frequencies, you may have the
        >same from say 162.400 and 154.770 ending up on 147.140 MHz. It's always
        >a good idea to attenuate a strong RF signal near your receiver's location.
        >
        >You could also put say a Micor or MASTR II front end in line with your
        >scanner, but that would likely reduce the sensitive range to a MHz or
        >so. Since you have the generator, you could easily tune one of those
        >front ends to the band of interest.
        >
        >I've put notch cavities on equipment located at the same site and had
        >usable reception as close as 60 kHz away from the transmitter. You are
        >dealing with a much easier situation.
        >
        >Joe M.
        >
        >Andy Carstarphen wrote:
        >> It looks like it is mixing occurring in the front of the receiver. I set my service monitor to generate a signal on 154.740 and as soon as I placed it into GENerate mode, it duplicated the event. I turned the IF shift on for that channel but it made no difference. I was performing a 2 meter audit using the logging feature of Free Scan. I'll just have to handle that particular frequency manually.
        >>
        >> Thanks,
        >>
        >>
        >> Andy Carstarphen - WY5V
        >>
        >>
        >>> ________________________________
        >>> From: MCH <mch@...>
        >>> To: BCD396XT@yahoogroups.com
        >>> Sent: Tuesday, August 2, 2011 7:52 PM
        >>> Subject: Re: [BCD396XT] BCD396XT Intermediate Frequencies / image reception
        >>>
        >>>
        >>>
        >>> What you are describing has nothing to do with the XT - or any radio for
        >>> that matter. It is classic 2A-B intermod (AKA mixing). Where it is
        >>> mixing could be anything from the PA of the NOAA transmitter to a loose
        >>> connection on your roof. It could also be mixing in the front end of
        >>> your receiver.
        >>>
        >>> CTCSS will only help if the 147.080 frequency CTCSS is different than
        >>> that used on 154.740 MHz. Or, you can use an RF filter (AKA cavity)
        >>> which may or may not help the problem. It will help if the mix is in the
        >>> front end of your receiver. It will not help is the mix is anywhere else.
        >>>
        >>> You would likely hear the same thing on any receiver tuned to 147.08 MHz.
        >>>
        >>> The only significance of 7.66 MHz is that it is the separation of the A
        >>> and B transmitters, and of the A transmitter and your receive frequency.
        >>>
        >>> The same thing will often happen with any two transmitters where you are
        >>> trying to monitor a frequency that is 2A-B MHz away.
        >>>
        >>> In your case:
        >>>
        >>> 162.400 = B
        >>> 154.740 = A
        >>> 147.080
        >>>
        >>> Joe M.
        >>>
        >>> ANDY - WY5V wrote:
        >>>> In looking up the specifications for the scanner I find the following information:
        >>>>
        >>>> 1st IF: 380.7 to 380.8 MHz / 265.5 to 265.6 MHz
        >>>> 2nd IF: 10.8 MHz
        >>>> 3rd IF: 450 kHz
        >>>>
        >>>> I know that there is an IF shift feature. But before I use it, I want to know if there is anything special about 7.66 MHz. The reason I ask. I have discovered that when two particular transmitters are on the air, I hear them both on another frequency. Here are the stations involved:
        >>>>
        >>>> 162.400 KEC56
        >>>> 154.740 KLD811
        >>>> 147.080 RX only
        >>>>
        >>>> KEC56 is the local NWS All Hazards Radio station. So it is on the air continuously. When KLD811 keys up, I hear them both on my scanner on 147.080. Here is the arithmetic:
        >>>>
        >>>>
        >>>> 162.400 - 154.740 = 7.66 MHz
        >>>> 154.740 - 147.080 = 7.66 MHz
        >>>>
        >>>> So, does anyone know if there is anything special about 7.66 MHz inside the BCD396XT?
        >>>>
        >>>> Andy
        >>>>
        >>>>
        >>>>
        >>>> ------------------------------------
        >>>>
        >>>> Yahoo! Groups Links
        >>>>
        >>>>
        >>>>
        >>>>
        >>>> ----------------------------------------------------------
        >>>>
        >>>>
        >>>> No virus found in this incoming message.
        >>>> Checked by AVG - www.avg.com
        >>>> Version: 9.0.901 / Virus Database: 271.1.1/3806 - Release Date: 08/02/11 14:34:00
        >>>>
        >>>
        >>>
        >>>
        >>
        >> [Non-text portions of this message have been removed]
        >>
        >>
        >>
        >> ------------------------------------
        >>
        >> Yahoo! Groups Links
        >>
        >>
        >>
        >>
        >
        >
        >
        >

        [Non-text portions of this message have been removed]
      • Tony Langdon, VK3JED
        ... Sounds like it s the front end of the scanner that s causing the intermod. 73 de VK3JED / VK3IRL http://vkradio.com
        Message 3 of 10 , Aug 3, 2011
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          At 04:14 PM 8/3/2011, you wrote:
          >Texas currently uses a 20 KHz band plan. I will simply use a
          >different radio to monitor that frequency for activity. Of the
          >nearly 300 frequencies I have programmed in, this is the only one
          >that has encountered the problem.

          Sounds like it's the front end of the scanner that's causing the intermod.

          73 de VK3JED / VK3IRL
          http://vkradio.com
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