Announcement

Collapse
No announcement yet.

VERY Close call

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • VERY Close call

    So I was outside DXing and I thought I saw a flash of lightning but I looked up and saw stars and I didn't hear thunder so I ignored it, then a couple minutes later it started sprinkleing then literally 5sec later it starts POURING very hard rain and I basically threw my ka1103 in my sweatshirt pocket and ran inside leaving the pole up and dryed it off and luckly it wasn't really wet at all, whew...
    That was quite the weird storm it only lasted about a total of 15sec.

    PS: on 330khz I hear the exact same audio as WCLO (1230khz)? STL? Image? Something else?

  • #2
    I've seen storms like that.
    330khz should have nothing but non-directional beacons, I think. Not an STL.
    Mike B.
    Enfield, CT
    -72° 30' W/41° 59' N
    FN31RX


    Online since 1999 and still going at

    mikesdx.com

    Comment


    • #3
      I no longer have LW radio, but ISTR hearing spurs/images of WINZ 940 on a relative's rig. I say it has to be the radio itself.

      cd

      Comment


      • #4
        Strange. On both counts.

        WCLO on 330 is an image. This will get a bit long

        Nearly all radios use Edwin Armstrong's "superheterodyne" circuit.

        If you want to listen to WCLO -- if you tune to 1230 -- a "local oscillator" circuit in the radio is set to generate a "dead air" signal on 1680. This signal is sent to a "mixer", where it is mixed with signals coming from the antenna. With regard to WCLO, this mixer has four outputs:

        1230 (WCLO)
        1680 (dead air signal)
        450 (1680-1230)
        2910 (1680+1230)

        The output of the mixer goes to an "intermediate frequency amplifier", which contains a sharp filter passing only 450KHz. The other three signals are discarded. 450KHz is amplified, demodulated, and sent to the speaker -- and you hear WCLO.

        Now, let's say you tune to 330 instead. The local oscillator is retuned to 780. The four outputs of the mixer:

        330 (navigation beacon)
        780 (dead air signal)
        450 (780-330)
        1110 (780+330)

        And again, the intermediate frequency amplifier amplifies the signal on 450KHz and feeds it to the speaker.

        The advantage of this circuit is that most of the frequency selectivity and amplification happens at 450KHz regardless of what frequency you're actually listening to. You don't have to retune multiple circuits every time you change frequency.

        =====

        Going back to our 330 example though.. Again, we have the local oscillator running on 780. What happens if, along with the navigation beacon on 330, we have a strong signal on 1230 from WCLO?

        1230 (WCLO)
        780 (dead air signal)
        -450 (780-1230)
        2010 (780+1230)

        There's no such thing as negative frequency but that just means the signal on 450 coming out of the mixer is "upside-down". You can't tell the difference. When tuned to 330, your radio will *also* respond to signals on 1230. And across the board, you'll hear things 900KHz above the frequency you're tuned to. 480 & 590 in Beloit; 170, 410, 580, and 650 in Madison; etc...

        To prevent this phenomenon, most radios contain some kind of filter between the antenna and the mixer. This filter prevents signals 900KHz above the tuned frequency from reaching the mixer. However, no filter is perfect. It's especially difficult to provide a decent filter in a radio like the KA1103 that covers a wide variety of frequencies.

        ============

        The only frequency band authorized for studio-transmitter links is 944-952MHz. 942-944 and two microwave frequencies near 19GHz used to be available and stations authorized for those bands may still use them.

        There are however a wide variety of bands available for remote pickup (RPU) service:
        26MHz band (widely used to deliver cues *from* the station *to* field crews, and frequently heard rebroadcasting the station's air signal)
        153, 161, 166, and 170MHz bands
        450-451MHz, often paired with 455-456MHz

        and even more for television.
        Doug Smith W9WI
        Pleasant View, TN EM66
        http://www.w9wi.com

        Comment


        • #5
          Well, in my case, it's been over 40 years, so my memory is fuzzy....but I think that I was getting WINZ on more than one spot on the LW dial.

          cd

          Comment


          • #6
            Ok, don't neccicaraly get the whole local oscillator thing but I do get the filter thing.
            Also the whole reason I was on LW was to try and hear those beacons but I didn't hear any, any idea why?
            Are STLs "encrypted" or simply FM / AM? And how could i hear one? (RTL-SDR?)
            Are remote pickups the way live remote broadcasts get back to the studio? And what frequencies are things like sattelite downlinks for stuff like a syndicated show? And there's no way the speciffaly put it down to all the studios and or transmitters so can basically anyone get it by pointing it at it?

            Comment


            • #7
              STLs focus all of their power in one direction since they are a point to point wireless link, so you'd have to be right in the path of one to receive it. I imagine the newer ones are all digital. Satellites are mostly all up in the Ghz+ range and I imagine everything is digital by now. There are some unencrypted feeds that can be received using a FTA satellite receiver. I seem to remember back in the 90s when satellite TV was still analog you could pick up raw feeds from the national networks. This was back when you needed a huge dish and it had to be rotated to pick up different satellites. Satellite felt like uncharted territory back then, nowadays its no different than cable.
              DX Radios:
              Sony XDR-F1HD
              Sony XDR-S10HDiP
              Tecsun PL-390

              Comment


              • #8
                Not sure why you aren't hearing any beacons. According to several air navigation sites the one at the Janesville Airport is still active, on 375KHz. It should be sending "JVL" in Morse. (.--- ...- .-..) The Google aerial photo does show the building that used to house it is still there. I can't see the antenna but I wouldn't be surprised if it doesn't show up in aerial photos.

                Many STLs are now digital although I think some are still analog FM. WCLO is, for some reason, authorized for *two* STLs. One is on 951.5 and originates in downtown Janesville, on Parker Place between Milwaukee and Court Streets. The other is on 944.5 and originates at the WJVL transmitter site. WJVL is licensed for a STL on 948.5 which originates at the Parker Place site -- and terminates at the *AM* transmitter site. I'm thinking there's a typo in there somewhere. If any of these are analog I would expect they could be heard on a RTL-SDR.

                Remote pickup stations (RPU) *used* to be how live remotes got back. Today they're more often done by cellphone. (and with data service and better codecs than are used for voice calls, you could get very good audio quality over a cellular connection) WCLO is still authorized for five mobile units on 455.7MHz. (transmitting to an automatic relay station which retransmits their signals on 450.7) This kind of thing is usually used for newsgathering and may not be intended to be put on the air. There's also a 15-watt transmitter on 450.85 at the AM transmitter, which is probably used to relay transmitter telemetry back to the studio.

                Satellite downlinks are in the C-band (3700-4200MHz) and Ku-band. (11700-12200MHz) Most are digital these days. (but often, a standard protocol with no encryption is used, so you can monitor if you have a digital receiver) No, they generally don't spot-beam that kind of thing, so they're accessible pretty much anywhere in North America.
                Doug Smith W9WI
                Pleasant View, TN EM66
                http://www.w9wi.com

                Comment


                • #9
                  In the early 1970s an AM station had a DJ in a promo van at a strip mall about a mile west of here. Their RPU was in the 170-MHz band, easily heard on my hi-VHF http://www.qsl.net/wa5iyx/GEN-1451a.htm set. Their tiny Yagi on the van was pointed towards the Tower of the Americas (where the TV remotes still beam their microwave horns at). In the 1990s, while looking for some CATV egress in the 170-MHz zone with a BC-50XL and its whip, I heard this strong RPU from several miles away.

                  73, Pat - WA5IYX

                  Comment

                  Working...
                  X