[RTTY] Spot frequency

Joe Subich, W4TV lists at subich.com
Sun Jun 13 19:49:20 PDT 2010



One minor correction ...

 > Menu 6-5 "Packet tone frequency":  Set to the MARK tone (2125 default)

By setting "Packet tone frequency" to 2210 (Mark + shift/2) the filters
will be properly centered on the AFSK tones.   The 85 Hz offset is not
a problem unless you try to use the 250 Hz filter pair.  "Packet tone
frequency" should be set to the "center" of the RTTY tones.

73,

    ... Joe, W4TV


On 6/13/2010 10:27 PM, Joe Subich, W4TV wrote:
>
>   >  So how exactly is this done?
>
> If you must use AFSK - even though the FT-1000 and its siblings make
> FSK so much easier - use the MENU SYSTEM to set things correctly (it's
> all in the manuals).
>
> Menu 6-4 "Packet Display Offset":  Set to the MARK tone (-2.125 for LSB)
> Menu 6-5 "Packet tone frequency":  Set to the MARK tone (2125 default)
> Note: if you use AFSK tones other than the traditional "High Tones"
> (2125/2295) replace -2.125/2125 with your MARK tone frequency.
>
> It is as SIMPLE as that to make the PKT mode in the FT-1000 family of
> transceivers display correctly when using PKT mode for AFSK.
>
> 73,
>
>      ... Joe, W4TV
>
>
> On 6/13/2010 9:06 PM, Jerry Rappel wrote:
>>
>> That said, good rigs won't have this problem if you set them up
>> correctly. The menu of the FT-1000MP for example, allows you to apply
>> a dial offset to the AFSK ("PKT") mode.
>>
>>
>> ---------------------------------------
>>
>>
>>
>> So how exactly is this done?
>>
>> Thanks,
>>
>>
>>
>> Jerry  WWØE
>>
>> ==============================
>>
>>
>>
>>> From: chen at mac.com Date: Sun, 13 Jun 2010 18:01:08 -0700 To:
>>> rtty at contesting.com Subject: Re: [RTTY] Spot frequency
>>>
>>>
>>> On Jun 13, 2010, at 5:18 PM, Gary AL9A wrote:
>>>
>>>> I seem to remember this was due to the 2125 Hz shift. Is this a
>>>> difference between running FSK or AFSK?
>>>
>>>
>>> By convention, RTTY signals are identified by the Mark frequency.
>>>
>>> Most radios when operated in FSK mode will display the mark carrier
>>> as the VFO dial frequency. So, the problem is most likely *not* be
>>> originating from you.
>>>
>>> But take the case of an AFSK op who just worked you (and presumably
>>> zero beat with you)...
>>>
>>> If his VFO dial is showing the suppressed carrier frequency of an
>>> LSB transmitter, and he using the 2125/2295 tone pair, then his
>>> (and your) mark carrier will be 2.125 kHz below his dial frequency.
>>> If he is spotting from his VFO dial, the spot will read 2.1 kHz
>>> higher than your actual mark frequency.
>>>
>>> Now, what if he is using USB?
>>>
>>> In this case, assuming he is using the same 2125/2295 tone pair,
>>> his mark carrier will be 2.295 kHz above his suppressed carrier.
>>> (Notice that the mark, by convention is always the higher frequency
>>> of the two RF carriers.) If he is reading off a VFO dial that
>>> displays the SSB suppressed frequency, his packetcluster spot will
>>> then be 2.3 kHz too low.
>>>
>>> That said, good rigs won't have this problem if you set them up
>>> correctly. The menu of the FT-1000MP for example, allows you to
>>> apply a dial offset to the AFSK ("PKT") mode.
>>>
>>> Even if the radio does not have that feature, software modems often
>>> have a place where you tell it to how to label the waterfall
>>> frequency. cocoaModem for example has a VFO offset box, plus a menu
>>> to tell it if you are using USB/LSB and it will apply the
>>> arithmetic gymnastics to display the number that has to be added to
>>> or subtracted from the VFO dial to get the actual frequency of your
>>> RTTY mark. cocoaModem will in fact reverse the waterfall (lower
>>> tones appearing on the right side of the waterfall instead of
>>> higher tones always on the right) when you transceive in LSB so
>>> that the waterfall will show the higher RF carrier always to be on
>>> the right of the waterfall.
>>>
>>> With all the tools at our fingertips, (including a calculator :-),
>>> there should be no excuse for not spotting the mark frequency of an
>>> RTTY signal properly.
>>>
>>> 73 Chen, W7AY
>>>
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>>> RTTY at contesting.com
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