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7987RE: Re: [RADIOSHACKDX394] Re: "Hollow" sound with TWO Antennas?

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  • josephrot
    Sep 30, 2013
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      Alas, it's "great" only if it happens to be the cause.


      You do have a YouTube or other audio recording of the  "hollow sound" in action ?


      Unless me brain skipped an earlier message noting a recording...


      Joe Rotello / Knoxville, TN / USA

      ---In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

      Great idea!!!! Bad speaker. So I bypassed the speaker by using the headphones. NOPE still there goes away below 13 and above 18


      Sent from my iPhone

      On Sep 29, 2013, at 13:30, <joerotello@...> wrote:


      Ernie, Tom and All...


      I remember back about 2003 or 2004, and we were a group of engineer/technicians being Dr. Kildare "diagnosing" a receiver that sounded very "hollow" for two stations adjacent frequency-wise. Only happened on *those* two stations, too. No, it wasn't a DX-394.


      We tested, boy did we test...

      Was it Tom's propagation or reflected signals, or some transmitter induced receiver mixer mania ?

      Nope. We used every decent testing and display hardware, and nothing looked wrong at all, as everything tested fine.


      Was it Joe's receiver front-end over load, perhaps two very strong signals mixing just right in an RF related sense, producing an odd result ?

      Again, Nope. We again used every decent testing and display hardware, and nothing looked wrong at all...everything tested fine.

      Do you all realize how embarrassed we all were when the true and proven culprit turned out, in this one case, to be....


      A defective dual-cone (wide range) speaker IN the receiver.


      Yes, the speaker. But how ?

      Because it ONLY went "sour" on those two received signals, as they were transmitted "just right" and they produced a deep bass "hollow sound" that was clearly heard, repetitively happened, exceedingly annoying as heck, happened at low-to-"intermediate" volume all the same, the receiver of course had no tone controls at all so we had nothing to tone adjust to test...

      Well, as I said, darn embarrassing to all us "yeah, right, real smart engineers, alright..."

      OK, so who solved the above puzzle?

      We were administered the Coup de grĂ¢ce in a manly humiliating way, too. One woman in the area piped up "Guys, you know that sort of sounds like my husband's stereo when he blew a speaker out or something like that..."

      We looked at each other, took her "consulting" advisory, and cracked the receiver case. Each of the three or four of us took turns pushing on the speaker cone (boy, did we look stupid) and we heard it audibly "rasp" a little.

      Being of good cheer, more or less, we pulled a nice similar size new speaker off a shelf and replaced it. The Lady was right.


      The moral of Joe's overly long, true life, raise-my-hand-and-swear story is:



      Call that woman !!

      Joe Rotello / Knoxville, TN / USA

      ---In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

      Nice. Now i really have a headache!! Great stuff and wow am i glad i asked about what I was observing/hearing.
      I was just at the dials and was hearing the "hollow" sound again, I decided to try it in a known freq. I chose 15mhzWWV and yes the hollow was there. I disconnected the E/W long wire the hollow went away but when I disconnected the N/S wire it remained.


      On Sun, Sep 29, 2013 at 9:25 AM, <joerotello@...> wrote:

      Tom...and Ernie...

      When we have tested the situation Ernie has described, it was more experiences signal overload than propagation or "dual-signal temporal arrival" as it used to be called at NASA years ago. And no, we did not really "blame" the receivers or in this case the DX-394.

      We verified the "hollow" sound in many cases and with the two DX-394 users with the assistance of spectrum analyzer, scope and a dual-signal generator for producing frequencies other than the two strong stations that can cause receivers to exhibit the symptom, which we were fortunate to also be able to test with.

      We brought along an SDR equipped unit as well, and in the case of the DX-394, reproduced the symptoms on the DX-394, and the hollowness or lack of it was also noticed on the SDR, with it's various filters and DSP to test and adjust against.

      Yes, a "hollow sound" can be caused by propagation / ghost / reflection effects, but in our humble experiences, it was exhibited on the DX-394 as more overload and sum+difference situations causing it, especially on SW, but also heard occasionally on AM.

      I think one or two of the Wikipedia author's and myself and another engineer corresponded with the authors of that page, and we were informed that eventually they will update the page to show other possibilities. The author's are sometimes hard to track down, but it's interesting to "meet" them over and above Wikipedia entries.

      So, there can be at least a few explanations...yes..

      But what's most important is that we users be aware that the situations and causes do exist, and many will hear such sound in ones electronic travels.

      Joe Rotello / Knoxville, TN / USA
      (no message history for brevity)

      Remember that when you think you have it all figured out... you wake up to start all over again!
      Trust yourself and MOST times you will not be disappointed
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