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   Home   Help Search  
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Author Topic: Finding the DX TX freq on FT8  (Read 4529 times)
W1JTO
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Posts: 65




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« Reply #45 on: November 05, 2017, 02:15:14 PM »

Dumb  question,  But if the calling freq is +1500 how does the answering station know what freq to work from ?

So in split I call CQ in 7074 (7075.5, right ?) how do I inform the "hounds" where to go to finish theCQ with me ?

Thank you in advance.

73 John W1JTO
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VA3VF
Member

Posts: 819




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« Reply #46 on: November 05, 2017, 02:36:02 PM »

Dumb  question,  But if the calling freq is +1500 how does the answering station know what freq to work from ?

So in split I call CQ in 7074 (7075.5, right ?) how do I inform the "hounds" where to go to finish theCQ with me ?

Thank you in advance.

73 John W1JTO


You don't inform them. If they receive your signal, it'll show on their band activity window. They then call you on any frequency they want within the segment, and if you receive their signal, it'll show on your band activity window. There is a possibility that multiple stations will call you, each on a different frequency. This is how FT8 split works.
« Last Edit: November 05, 2017, 02:42:51 PM by VA3VF » Logged
AA4PB
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Posts: 14339




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« Reply #47 on: November 05, 2017, 04:21:29 PM »

"We know that the SSB passband rolls off above and below 1500 Hz by default for most rigs, unless we have tailored the TX on the rig (some of the newer rigs have TX filter shaping).  So, our signal output will be diminished if we're not sending the tone at 1500 Hz"

This isn't true on most rigs which have decent IF filters. The filter may begin to roll off below 300Hz and above 2700Hz but the Tx output should be within a dB or so between 300Hz and 2700Hz. If it began to roll off as soon as you moved away from 1500Hz you'd have some pretty weird sounding voice on SSB.

The reason for split is as presented in the WSJT documentation, if you are generating any harmonics then keeping the audio signal in the upper range will move the harmonics outside the upper edge of the filter so they won't be transmitted. The fact is that if you are not overdriving any of your audio stages then you shouldn't be generating any harmonics so you can use any audio frequency between 300Hz and 2700Hz without an issue with transmitting harmonics. Think about PSK31 and all the other digital modes including keying CW via audio - None of that software even has a "split" function to keep your audio at 1500Hz.

I just finished some testing with my IC-756PRO. For the same input audio level I actually get about 10W more output at 300Hz than I do at 1500Hz or 2700Hz. I expect that may be caused by the frequency response of the isolation transformer in the interface rather than the radio itself.

« Last Edit: November 05, 2017, 04:40:34 PM by AA4PB » Logged

Bob  AA4PB
Garrisonville, VA
W1JTO
Member

Posts: 65




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« Reply #48 on: November 07, 2017, 02:31:55 PM »

Thanks for the noob tutorial... Will try it out this weekend.

So call CQ on 7075.5 right ?

John
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AA2UK
Member

Posts: 319




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« Reply #49 on: November 08, 2017, 04:11:46 AM »

Thanks for the noob tutorial... Will try it out this weekend.

So call CQ on 7075.5 right ?

John
\ 7074
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K0UA
Member

Posts: 1380




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« Reply #50 on: November 08, 2017, 06:10:09 AM »

Thanks for the noob tutorial... Will try it out this weekend.

So call CQ on 7075.5 right ?

John

WSJT-x will take you to 7074 as the base frequency when you go to 40 meters.  If your audio frequency is 1500hz you will be at 7075.5  But you will have to find a clear "hole" where ever you can.  40 meters will be very crowded most of the evening and night time.  If you want to call CQ, you will just have to fit in.  There is just one FT8 base frequency, of 7074 so stay there and move your audio frequency around as needed.  Turn on split with "fake it" selected and the program will manage your rig so that your audio frequency stays within the transmit bandwidth "sweet spot" of your rig.   Have fun.
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W1JTO
Member

Posts: 65




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« Reply #51 on: November 08, 2017, 01:19:47 PM »

Thanks for the noob tutorial... Will try it out this weekend.

So call CQ on 7075.5 right ?

John

WSJT-x will take you to 7074 as the base frequency when you go to 40 meters.  If your audio frequency is 1500hz you will be at 7075.5  But you will have to find a clear "hole" where ever you can.  40 meters will be very crowded most of the evening and night time.  If you want to call CQ, you will just have to fit in.  There is just one FT8 base frequency, of 7074 so stay there and move your audio frequency around as needed.  Turn on split with "fake it" selected and the program will manage your rig so that your audio frequency stays within the transmit bandwidth "sweet spot" of your rig.   Have fun.

OK do both split options "fake it" and "rig" require CIV control of my 7000 ?

73  John W1JTO
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K0UA
Member

Posts: 1380




Ignore
« Reply #52 on: November 08, 2017, 01:30:12 PM »

Thanks for the noob tutorial... Will try it out this weekend.

So call CQ on 7075.5 right ?

John

WSJT-x will take you to 7074 as the base frequency when you go to 40 meters.  If your audio frequency is 1500hz you will be at 7075.5  But you will have to find a clear "hole" where ever you can.  40 meters will be very crowded most of the evening and night time.  If you want to call CQ, you will just have to fit in.  There is just one FT8 base frequency, of 7074 so stay there and move your audio frequency around as needed.  Turn on split with "fake it" selected and the program will manage your rig so that your audio frequency stays within the transmit bandwidth "sweet spot" of your rig.   Have fun.

OK do both split options "fake it" and "rig" require CIV control of my 7000 ?

73  John W1JTO
Yes.  As does sequencing / keying of your rig.  I can't imagine using FT8 with CAT control of a rig.  Although a couple of people here have.  One mentioned a homebrew rig with not Computer control available.  I would have thought it nearly impossible, but apparently not. It sure would be a big PITA
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