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Thread: ICOM 746 Pro Off Frequency

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  1. #1

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    I have a new (6 months) ICOM 746 Pro rig. I sent it in for service to ICOM to fix a PA problem back in August.

    Now that I have it back, I've had several reports that it is off frequency. Specifically, it is .03 Hz off. It doesn't drift, always the same.

    Does anyone know of a way I can fix this without shipping it back in? Is there a user servicable method for tuning the VFO on the rig? Any programmable way through the controls?

    Many thx,

    73 de ABYW
    - Rodger

  2. #2
    Join Date
    Nov 2002
    Location
    Houston, TX
    Posts
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    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (ab0yw @ Sep. 21 2003,21:40)</td></tr><tr><td id="QUOTE">Now that I have it back, I&#39;ve had several reports that it is off frequency. #Specifically, it is .03 Hz off. #It doesn&#39;t drift, always the same.[/QUOTE]<span id='postcolor'>
    How the #### can you measure that&#33;?

    For ham use, there is no real reason to have a super accurate frequency readout. I would be suspicious of anyone who thinks their dial readout is accurate, especially on SSB. Even on CW, the difference in what tone people prefer can cause a few tens of Hz apparent difference between readout comparisons.

    The only real way to tell what frequency is indicated is to zero-beat a CW signal. Since SSB doesn&#39;t have a carrier, that won&#39;t work. Also the audio of most rigs filters out the low frequencies, so as you get to zero-beat you lose the audio and can never quite tell, certainly not down to a Hz or 2.

    Personally I wouldn&#39;t worry about the difference. Let the observers think they are accurate. It&#39;s their dellusion.
    73,
    Walt, W5ALT
    ARRL Life Member
    Member SPAR [URL="http://www.spar-hams.org"]www.spar-hams.org[/URL]

  3. #3

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    Well, it is annoying, because, when I tell someone to go to a particular freq, they have to tune high to get my voice clear. I&#39;m not a stickler for the numbers, but it was noticed several times.

    I have a freq counter that I&#39;m going to try to verify it on. Anyhow, anyone have any ideas?

  4. #4
    Join Date
    Mar 2001
    Location
    Bremerton, WA
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    It better be a darn expensive frequency meter if it&#39;s going to measure 0.03 Hz&#33; That&#39;s WELL below the threshold of human hearing.

    Frequencies for hams are generally &quot;plus or minus QRM&quot;, so if you told someone to meet you on 21.275, he&#39;d more than likely listen around that frequency to find the spot least likely to cause interference to QSOs already in progress. Don&#39;t sweat the exact frequency unless you&#39;re really close to the band edges.

    I really don&#39;t think you&#39;re 0.03 Hertz off. It might be closer to 0.03 KHz, which is like 30 Hertz.
    Semper ubi sub ubi. 73
    K7KBN CWO4 USNR Ret.

  5. #5

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    Yes, yes, it is .03 KHz. Duh.. sorry guys&#33; Yes it sounds like QRM.

    Thanks

  6. #6
    Join Date
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    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (ab0yw @ Sep. 21 2003,22:47)</td></tr><tr><td id="QUOTE">Yes, yes, it is .03 KHz. #Duh.. sorry guys&#33; #Yes it sounds like QRM.[/QUOTE]<span id='postcolor'>
    If someone is worried about 0.030 kHz = 30 Hz on a SSB signal, then they need serious counseling&#33; I can change the tuning by a few tens of Hz depending on what pitch I think your voice should sound like.

    If you&#39;re really worried or just curious, try zero-beating WWV and check your readout. You better have a darned good frequency counter if you try that route. Most don&#39;t display enough digits to read down to the Hetz range when the signal is in the MegaHertz range. You won&#39;t be able to use SSB, either, since the signal will be offset from the non-existent carrier frequency. In CW, mode don&#39;t forget to account for the CW tone offset that most rigs use.

    I wouldn&#39;t worry about it. I would worry about anyone who thinks that difference is in any way important, though. They need help understanding their radios. That what the RIT or Clarifier knob is for.

    73,



    Walt, W5ALT
    ARRL Life Member
    Member SPAR [URL="http://www.spar-hams.org"]www.spar-hams.org[/URL]

  7. #7

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    .03 KHz is 30 Hz&#33; Virtually no one can tell the difference in that amount of frequency shift&#33; Do you mean 300 Hz or 0.300 KHz?

    Frankly, unless you have very recently calibrated the reference frequency oscillator in the unit to WWV or other reliable precision source, your dial reading and your absolute transmitting frequency are going to differ. I have seen digital readouts that are well over 2 KHz from what the actual frequency is. This is due to drifting of the reference oscillator.

    If you can receive WWV on the receiver portion, tune in the exact frequency (10.00000 MHz, 5.00000 MHz, 15.00000 MHz, etc.) with the receiver in the SSB portion. Then adjust the reference oscillator frequency until the signal is zero beat (you cannot hear any &quot;beat&quot; note and the &quot;S&quot; meter is fluxuating very slowly). If the reading changes, then adjust the tuning to the &quot;proper&quot; frequency and adjust the reference oscillator again. Do this until the signal is zero beat at the proper reading on the readout.

    Make sure that the RIT is not turned on&#33; This will make sure that the transmit signal and the receive signal are the same.

    As for someone telling you to go to a specific frequency, their readout may not be exactly in tune with yours. For example, recently two local amateurs who had been working FM and not SSB got 2 meter SSB equipment. They both dialed in 144.2000 MHz and each one sounded like &quot;Donald Duck&quot; to the other. I was called on the telephone and zero beated one amateur and then had the other one transmit. He was about 600 Hz off frequency. I then informed them to ignore the actual reading of the unit but to tune for when the audio sounded normal. It was then that they compared frequency readings and they differed by about 600 Hz. Frankly, they both were not &quot;exactly&quot; on 144.2000 MHz even though one of the units read such. According to my service monitor they were about 200 Hz low&#33; The service monitor is a &quot;bit&quot; more accurate than the amateur equipment (I calibrate all three of my service monitors to WWV on a very regular basis).

    Anyway, I &quot;love&quot; to hear stations discussing just who is on the &quot;right&quot; frequency or else trying to measure the frequency by just using their dial. Very seldom are they within 100 Hz of where they think they are&#33; Often they are 200 to 300 Hz or more away from what their dials are telling them. Again, this is using one of my service monitors to measure the frequency. By the time you get up to 2 meter SSB, the differences can be more like 1 KHz or more.

    Glen, K9STH

  8. #8

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    Thanks for the advice. According to my MFJ-259B (which isn&#39;t the most precise piece of equipment in the world), I am 400 Hz off frequency on 20m.

    The difference is that I tell someone to go to 14.340.00 and we both zero in. I am then &quot;twangy&quot; until they shoot up a bit. My cousin (who is stateside) pointed this out this weekend. He also sounded &quot;twangy&quot; to me, so I don&#39;t think this is anyone&#39;s imagination.


    To verify we both weren&#39;t slightly off frequency, I then asked another ham in a QSO on 20m. We both noticed the same thing, and I &gt;repeatedly&lt; had him move up and down to verify I was off frequency. If that wasn&#39;t convincing enough, I went to 17m and did the same with another contact.

    My question was, is there a way for a user to callibrate the 746 using the built-in controls? This problem did not exist prior to sending it in for service. It is annoying to me, and obviously callibration is possible.

    Thanks and 73

  9. #9
    Join Date
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    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (ab0yw @ Sep. 22 2003,08:27)</td></tr><tr><td id="QUOTE">My question was, is there a way for a user to callibrate the 746 using the built-in controls? #This problem did not exist prior to sending it in for service. #It is annoying to me, and obviously callibration is possible.[/QUOTE]<span id='postcolor'>
    Glen answered your question above. If you really want to know how close your rig is, don&#39;t check it in SSB mode with other SSB signals. Zero-beat against WWV or another standard AM signal.

    73,
    Walt, W5ALT
    ARRL Life Member
    Member SPAR [URL="http://www.spar-hams.org"]www.spar-hams.org[/URL]

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