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Author Topic: Question on fldifi screen and operation -sweet spot?  (Read 122 times)

N3KXZ

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Question on fldifi screen and operation -sweet spot?
« on: February 27, 2023, 06:36:24 PM »

I guess I don't understand exactly what the fldigi screen is showing me.

The manual says "The sweet spot is the audio frequency at which your transceiver provides the best filtering for a particular signal type." I use the defaults. How does that default of 1500 relate to the frequency and the bandwidth? What does that 1500 number really mean? I thought it was the offset from the carrier frequency ...

For example, tonight I tuned into the WA1W digital bulletin at 7095, which tonight was on RTTY. When I tuned my rig to 7095 I could hear the signal but it did not appear on the screen at all. In order to put the signal directly in the "sweet spot" on the screen I needed to dial my rig to 7094.1. Does this mean that my digital counter is off? (BTW that is possible- I am using a 3rd party freq counter that includes a homebrew circuit for my vintage Kenwood TS-420.)

If 1500 is the carrier freq offset, then 7094.1 + 1500 = 7095.6, correct? is 600Hz a lot to be off? Or are they other considerations to make, like effects of propagation or other settings?

Thanks,
Keith
N3KXZ





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KE6SLS

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #1 on: February 27, 2023, 08:43:35 PM »

Hi Keith,

I guess the first fuzzy bit I have is understanding what a TS-420 is.  I've not heard of that rig so I am unable to offer any tips about that specific radio.

Here's a GREAT link for all FLDigi users:
https://orcadigitalnet.com/quick-start/

In a nut shell.  ALL digital modes are in USB mode.  Many new ops don't realize this as their radios will default to LSB since that is the typical mode for 75/80 meters.  So make sure your rig is in USB while you're enjoying the digital modes.

Since this is an old radio, you will likely have to listen for callers and do your best to center on their frequency on the FLDigi water fall.  It's especially easy if the ops use the "TUNE" button on FLDigi, you will see that and can easily click on that signal in the water fall with your mouse.

The sweet spot was chosen over  a decade ago as being the default in FLDigi.  Very rarely do I see stations not using the 1500hz.  Now a caveat is working PSK31 mode.  This is an ultra-narrow mode where many ops can use a single frequency (on radio dial) and simply click on any given audio signal on the waterfall to QSO with.

Another very handy tip is make sure to turn on the RxID at the top right of FLDigi.  If an op is transmitting a TxID your station should hear that ID and automatically change into the correct operating mode the sending station is using.

If your radio drifts, you will have to compensate for it manually in FLDigi.  You can use the arrows on either side of the water fall frequency displayed center bottom of FLDigi screen.  However, if you are using PSK31 or any of the PSK modes, you can turn on the AFC button at bottom right and this should track that signal as you qso.  Other modes, you will want to turn off the AFC.

I hope you enjoy the modes!

73
Jaye
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N3KXZ

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #2 on: February 27, 2023, 09:13:24 PM »

Hi Jaye- thanks for your comments. I apologize there is a typo in my original post- I have a Kenwood TS-520, not a TS-420. And yea, set rig to USB for digital modes :-) Haven't used the AFC control yet, thanks for mentioning that.

Keith
N3KXZ
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W1VT

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #3 on: February 28, 2023, 03:15:10 AM »

The new digi modes like FT8 are USB.
But RTTY is LSB!  I used RTTY back in 1982 with a TS-820S. 
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W3NR

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #4 on: February 28, 2023, 06:30:47 AM »

All modems in fldigi are USB, RTTY included.

Ed W3NR
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W1VT

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #5 on: February 28, 2023, 06:54:33 AM »

A USB modem used to decode traditional LSB modem can be used if the tones are reversed.
DX spots normally use the traditional LSB convention.  I use MMTTY for RTTY.

https://hamsoft.ca/pages/mmtty.php

N1MM Logger+ will integrate with it for RTTY contests.
https://n1mmwp.hamdocs.com/
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W3NR

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #6 on: February 28, 2023, 07:06:37 AM »

N1MM also supports fldigi as a RTTY modem and  fldigi is still set to USB, not LSB.

Dave did exactly what you said, he coded the RTTY modem to use USB,

This was done sometime in the 2006 or so time frame.

Ed W3NR
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W3NR

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #7 on: February 28, 2023, 07:51:18 AM »

Considering the age of the 520, being off 600Hz is acceptable, but not by much.

I would be glad if that all that it is off. Work around it and accept it is what it is.

Ed W3NR
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K9AO

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Re: Question on fldifi screen and operation -sweet spot?
« Reply #8 on: February 28, 2023, 08:21:37 AM »

Since the 520 does not have CAT control the "sweet spot" won't do anything for you.

The idea of it is that it'll move the current current cursor selection to the frequency you have set as the sweet spot. The idea here it to place the desired signal centered on a narrow IF filter if you have one so that you can cut the QRM if there is any. It will retune the radio to place the signal under the cursor centered at the sweet spot frequency you have set. Then you switch to a narrow filter or adjust the filters to narrow the passband as needed. By getting the desired signal at the filter center you have a very easy time to make these adjustments.

But your rig can't make use of this without CAT control.
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