Joe,
Your setup must be much better than my Kenwood TS-590S. On Tuesday evening I
did not see any of the stuff you observed. The W1AW signal looked normal to
me. If there is a problem with the W1AW Icom transmitters, I feel sure the
Station Manager will take corrective action.
I have seen some bad looking signal on the bands but W1AW was not one of them.
Dick AA5VU
On Jan 29, 2013, at 10:10 PM, "Joe Subich, W4TV" <lists@subich.com> wrote:
>
> Dick,
>
> Unless you were observing the bulletins on *Monday* night local, don't
> be making any kind of statement about "local" interference. I've been
> doing this quite a few years - I was OO Coordinator in Ohio 30+ years
> ago and an OO for many years before than - I can certainly recognize
> the difference between audio harmonics in an AFSK (and PSK) generator
> and "local interference". I can also recognize symptoms that appear on
> one signal and not on other signals of similar strength nearby.
>
> That capture was made with an Elecraft K3/P3 - the P3 is an IF spectrum
> analyzer - its pick-off point is prior to any narrow filters and prior to any
> AGC action. Its results are not subject to misalignment (the
> improper receive mixer settings) and/or transceiver AGC action which
> makes "measurements" made with the waterfall of typical user digital
> software useless and inaccurate.
>
> > I think you owe the Joe Carcia, NJ1Q, the W1AW Station Manager and
> > this reflector a retracton for your public comments about the
> > "terrible" W1AW signal and your statement "….One simply *can not*
> > run "all sliders to the max" and "all knobs to the right" with AFSK."
>
> Since you called out the station ... I was not able to see a signal
> - either RTTY or PSK - on 20 meters at 2300Z Tuesday. I did look at
> the 80 and 40 meter PSK signals and noticed that they show the same
> problem of insufficient carrier suppression exhibited by the 20 meter
> signal (although they do not show the "audio harmonic" issues which
> were present on both the 20 meter AFSK and PSK31 bulletins).
>
> The 80 meter broadcast (www.subich.com/80M_carrier_-35dB.jpg) shows
> carrier only about 35 dB below the PSK level. The 40 Meter broadcast
> (www.subich.com/40M_carrier_-22dB.jpg) is even worse with carrier only about
> 22 dB below the PSK level as well as what appears to be 120 Hz
> "hum" (note the two "humps" above the 40 meter PSK signal was another
> (interfering) signal - it appeared and disappeared independently of
> signal being observed). Even if one assumed a 6dB "back off" from
> the CW/PEP level to prevent ALC action, carrier suppression of less
> than 40 dB is not exactly "good engineering practice."
>
> Modern DSP based transceivers are capable of essentially infinite
> carrier suppression. Absent excess IF gain and ALC, a properly aligned
> analog balanced modulator should provide more than 40 dB of carrier
> suppression and proper placement of the carrier on the skirt of the
> transmit IF filter should attenuate any residual carrier by another 10
> to 20 dB. With an "S9" (-73 dBm) signal, the carrier of any properly
> aligned SSB transmitter should be in the background noise at most urban
> or suburban receive locations on any frequency below 25 MHz.
>
>> The Station Manager uses a custom interface hard wired to the digital
>> ports on the rear - not via the Mic connector as implied in your
>> message.
>
> The Icom "ACC" port is not immune to over drive any more than a mic
> input; the only difference is that the clipping level is somewhat
> higher. However, Icom generally specifies pin 4 of the ACC connector
> at 100 mV RMS - not substantially higher than the level of an electret
> mic. The effects of audio clipping in the mic amplifier or modulator
> are quite distinctive and unmistakeable just as insufficient carrier
> suppression is clearly visible on a spectrum analyzer but not on the
> waterfall of most digital software - particularly when the receiver
> is tuned to the same carrier frequency as the transmitter.
>
> I stand by my observations and measurements - were I an active OO today
> I would have sent a notice to the station involved for all three
> transmitters. The signals do not exhibit good engineering practice
> and there were no unaccounted for sources of interference to make the
> observations ambiguous.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 1/29/2013 9:48 PM, Dick Kriss wrote:
>> Joe Subich, W4TV
>>
>> It was pretty obvious you were talking about a W1AW with the "terrible" AFSK
>> signal. There are no W1AW RTTY bulletins on Tuesdays so I listened to the
>> early BPSK-31 bulletin on 14.095 and on 18.102.5 using a Kenwood TS-590S
>> with a direct USB interface to fldigi-3.21.67 on an iMac with OS X 10.8.2.
>> The W1AW signal was on frequency on both bands with solid print, clean
>> looking BPSK-31 signals with none of the harmonics or birdies you mentioned.
>>
>> I am aware of the W1AW setup with Icom transmitters and the station manager
>> tries very hard to be sure each band dedicated transmitter is correctly
>> adjusted with no ALC showing. The Station Manager uses a custom interface
>> hard wired to the digital ports on the rear - not via the Mic connector as
>> implied in your message.
>>
>> I think you owe the Joe Carcia, NJ1Q, the W1AW Station Manager and this
>> reflector a retracton for your public comments about the "terrible" W1AW
>> signal and your statement "….One simply *can not* run "all sliders to the
>> max" and "all knobs to the right" with AFSK."
>>
>> You may want to check your setup for local interference causing the
>> harmonics and birdies you observed. There was no evidence of harmonics or
>> birdies on the early 29-Jan-2013 PSK-31 bulletin.
>>
>> Dick AA5VU
>>
>>
>>
>>> Date: Tue, 29 Jan 2013 10:38:45 -0500
>>> From: Joe Subich, W4TV <lists@subich.com>
>>> To: MMTTY@yahoogroups.com, RTTY <rtty@contesting.com>
>>> Subject: [RTTY] Bad AFSK
>>> Message-ID: <5107ED05.6010405@subich.com>
>>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>>
>>>
>>> Elecraft have taken the lead on FSK bandwidth - thanks to W7AY, K0SM
>>> and W0YK among others. Lets hope other manufacturers follow quickly.
>>>
>>> Yesterday evening as I was looking for some RTTY activity to try the
>>> new Elecraft "narrow FSK filter", I stumbled across another terrible
>>> AFSK signal. It just happens to belong to a well known club so I
>>> won't give the call here but I have contacted the trustee.
>>>
>>> However, I've posted a screen capture from my P3 that clearly shows
>>> what happens when over driving the mic input of an SSB transmitter at:
>>> http://www.subich.com/BAD_AFSK.jpg (the last spike at about 14.0972
>>> is a local birdie).
>>>
>>> Note this transmitter has not only "second harmonic" energy at
>>> +1 KHz/340 Hz shift and "fourth harmonic" energy at +2 KHz/680 Hz
>>> shift, it also shows insufficient opposite sideband suppression (or
>>> possibly IMD in the PA - it's impossible to tell which).
>>>
>>> One simply *can not* run "all sliders to the max" and "all knobs to
>>> the right" with AFSK. Any manufacturer or individual who says to
>>> do so is giving you bad advice. Again, unless you have the tools
>>> to make absolutely sure you are generating clean AFSK, *use FSK*,
>>> the clicks are far less objectionable than 2nd/3rd audio harmonics
>>> that are suppressed by -18 and -15 dB respectively. This capture
>>> was made during a fade - signal levels were generally much higher
>>> and even the spurious signals were well above -73 dBm (S9+).
>>>
>>> 73,
>>>
>>> ... Joe, W4TV
>>
>>
>>
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|
