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AB0L
 AB0L
(@3d0g)
Estimable Member Member
Joined: 1 year ago
Posts: 108
December 5, 2019 8:46 pm  

QRP Guys DSB (dual sideband) digital FT8 transceiver: https://qrpguys.com/digital-transceiver ($40)

 

Midnight Design Solutions digital mode SSB transceiver: http://www.midnightdesignsolutions.com/phaser  ($50)

 

AB0L (Formerly N0KAI)
-----
Kenwood TM-V71A, Kenwood TS-590S, Motorola XPR4550, TYT MD-UV380, Kenwood TH-D7A, BTECH UV-5X3, µBITX V5 QRP


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kx3dx
(@kx3dx)
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Joined: 1 year ago
Posts: 9
January 4, 2020 7:45 am  

The Phaser is SSB not DSB - a big plus.  The DSB one will booger up the other side-band.


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AB0L
 AB0L
(@3d0g)
Estimable Member Member
Joined: 1 year ago
Posts: 108
January 4, 2020 7:31 pm  
Posted by: @kx3dx

The Phaser is SSB not DSB - a big plus.  The DSB one will booger up the other side-band.

Meh. It's a hobby. We're perfectly entitled to operate DSB FT8. In fact, it wouldn't be difficult to take advantage of the "reversed" LSB signal to improve reception. The QRP guys unit gives you 3 (or more if you like) bands to operate in. You gotta drop another $50 for each band with the Phaser. Phaser puts out 4W whereas the QRP does maybe 1.5W on the usable USB signal. Phaser RF circuit is a better design IMO.

Tradeoffs. That's what makes this a hobby!

AB0L (Formerly N0KAI)
-----
Kenwood TM-V71A, Kenwood TS-590S, Motorola XPR4550, TYT MD-UV380, Kenwood TH-D7A, BTECH UV-5X3, µBITX V5 QRP


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kx3dx
(@kx3dx)
Active Member Member
Joined: 1 year ago
Posts: 9
January 5, 2020 7:19 pm  

Didn't mean to make that an acerbic comment - just informational.  If enough FT8'ers use DSB, the PSK32 sub-band would experience substantial interference.  Maybe I'm the only one still using PSK32...


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AB0L
 AB0L
(@3d0g)
Estimable Member Member
Joined: 1 year ago
Posts: 108
January 6, 2020 8:34 am  

I must not understand PSK. For example, take 40M FT8. That signal is 50Hz of bandwidth somewhere between 7,074,000Hz and 7,076,000Hz. At the high end, that would be 7,075,950-7,076,000Hz which would make the useless LSB signal be 7,072,000-7,072,050Hz, right? PSK is 7,040,000Hz. That's still over 32kHz away. I've seen a lot of grumbling about the DSB "interference" but I must be missing something as I don't see any bandwidth allocations that fall in the 7,072,000-7,074,000Hz range. LSB voice users, to be sure, but again, it's 50Hz QRM out of a 3kHz voice signal. Trivially easy to hear over, if it's even noticed at all.

The point about volume is a fair one, however. If everyone was doing 40M FT8 DSB, there would be a 2kHz chunk of LSB that voice couldn't use. OTOH, if DSB became that popular, WSJT-X would certainly be modified to take advantage of the inverse LSB signal for improved decoding.

AB0L (Formerly N0KAI)
-----
Kenwood TM-V71A, Kenwood TS-590S, Motorola XPR4550, TYT MD-UV380, Kenwood TH-D7A, BTECH UV-5X3, µBITX V5 QRP


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kx3dx
(@kx3dx)
Active Member Member
Joined: 1 year ago
Posts: 9
January 6, 2020 7:40 pm  

40m dx PSK-31 is 7030kc, USB; NA PSK-31 is 7070kc, USB.  Since FT8 is 7074kc, a 2500cy USB signal will have a LSB image at 7071.5kc, right on top of the PSK31 calling frequency.  Or is my in-my-head math wrong?  20M and the other bands are similar.

A ham making a DSB transmitter to play with is fine (actually encouraged!).  Marketing one as a commercial product is irresponsible.  In my opinion, of course...

Dave - kx3dx


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AB0L
 AB0L
(@3d0g)
Estimable Member Member
Joined: 1 year ago
Posts: 108
January 6, 2020 8:34 pm  

Goes to show I don't know squat about PSK. 😀 

My chart showed 7,040,000Hz. PSK-31 is apparently a different beast? FT8 sub-band ends at 2000Hz to avoid stomping on Olivia. That would make the LSB signal not a direct hit with PSK-31 but awfully close indeed.

Should a PCB and collection of lose electronic parts be considered a commercial product? The number of hams that could actually design their own DSB transceiver is quite small and rapidly growing smaller. I bet well less than half have even touched a soldering iron. Perhaps kits like these can be a gateway to bigger things, even with their known deficiencies?

AB0L (Formerly N0KAI)
-----
Kenwood TM-V71A, Kenwood TS-590S, Motorola XPR4550, TYT MD-UV380, Kenwood TH-D7A, BTECH UV-5X3, µBITX V5 QRP


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