Topics

uBITX - Digital mode power variation with input frequency #ubitx #ft8

Robbie Robertson
 

I'm new to uBITX, but used to operating digital modes (including FT8), but I'm not sure if what I'm seeing is a fault, or normal for the uBITX...
I'm using WSJT-X, and when I TX on the lower end of the 'spectrum' I get a much higher power output that the higher end (sorry I haven't got a power meter, but I can see the current being drawn from the power supply changing, and also the signal meter on my FT767 with no antenna attached).
This is strangely, the complete opposite I get when operating using the FT767 (i.e. high power at the higher end of the audio range).

Has anyone else experienced this,, or has a view on how to address it?

btw - I'm using a Easi Digi interface to feed PC headphone socket output into the mic socker connection (no mic attached).

Ghericoan
 

This seems normal to me now that I hear someone else is also dealing with it. It doesn't matter which digital mode I use, the power drops off a bit once I move either side of 1200hz in the waterfall. That 1200hz mark is peak current draw at 1.3A dc input, once I move down to 500hz or up to 1500hz there is roughly 200-300ma current draw difference.

Move from 1200hz up to 1800hz and the difference is 350-425ma less draw. I would stab a guess that it has to do with the response of the SSB filter.


Also, side note, I found the WSJT-X drives the ubitx much harder than FLDigi for some odd reason.

On Thu, May 24, 2018, 1:57 PM Robbie Robertson <robbie.robertson@...> wrote:
I'm new to uBITX, but used to operating digital modes (including FT8), but I'm not sure if what I'm seeing is a fault, or normal for the uBITX...
I'm using WSJT-X, and when I TX on the lower end of the 'spectrum' I get a much higher power output that the higher end (sorry I haven't got a power meter, but I can see the current being drawn from the power supply changing, and also the signal meter on my FT767 with no antenna attached).
This is strangely, the complete opposite I get when operating using the FT767 (i.e. high power at the higher end of the audio range).

Has anyone else experienced this,, or has a view on how to address it?

btw - I'm using a Easi Digi interface to feed PC headphone socket output into the mic socker connection (no mic attached).


--
----------
N5WLF, Greggory (or my nickname, Ghericoan)
General Class, Digital Radio Hobbyist

Bo Barry <bobarr@...>
 

Yep thats normal if the passband does not have a flat response. My Icom has a 3kHz passband and you can see the uneven signal pulses near the edges. Hang in the middle in a clear spot and you are OK. Check the fixed TX freq option. Use shift click to pick one out.
having a blast with mine on FT8. Bands are spotty, but I was at least heard in Germany with my 3 watts on 20 just now.
Bo W4GHV

Tim Gorman
 

This is because of how narrow the SSB filter is. Once you begin to move
out of the passband your power output will drop. The filter in the
ubitx is pretty narrow. It's not surprising you see a drop-off after
1600hz.

tim ab0wr

On Thu, 24 May 2018 10:57:27 -0700
"Robbie Robertson" <@Aardvarx55> wrote:

I'm new to uBITX, but used to operating digital modes (including
FT8), but I'm not sure if what I'm seeing is a fault, or normal for
the uBITX... I'm using WSJT-X, and when I TX on the lower end of the
'spectrum' I get a much higher power output that the higher end
(sorry I haven't got a power meter, but I can see the current being
drawn from the power supply changing, and also the signal meter on my
FT767 with no antenna attached). This is strangely, the complete
opposite I get when operating using the FT767 (i.e. high power at the
higher end of the audio range).

Has anyone else experienced this,, or has a view on how to address it?

btw - I'm using a Easi Digi interface to feed PC headphone socket
output into the mic socker connection (no mic attached).

Ralph Mowery
 

I have made some rough measurments and found the filter to be about 1600 to 1700 Hz wide.  If one wants to just the digital then the BFO frequency can be moved about 200 to 300 Hz to get the power up at the  higher audio frequencies.

 

On Thu, May 24, 2018 at 5:23 PM, Tim Gorman <tgorman2@...> wrote:
This is because of how narrow the SSB filter is. Once you begin to move
out of the passband your power output will drop. The filter in the
ubitx is pretty narrow. It's not surprising you see a drop-off after
1600hz.

tim ab0wr

On Thu, 24 May 2018 10:57:27 -0700
"Robbie Robertson" <robbie.robertson@...> wrote:

> I'm new to uBITX, but used to operating digital modes (including
> FT8), but I'm not sure if what I'm seeing is a fault, or normal for
> the uBITX... I'm using WSJT-X, and when I TX on the lower end of the
> 'spectrum' I get a much higher power output that the higher end
> (sorry I haven't got a power meter, but I can see the current being
> drawn from the power supply changing, and also the signal meter on my
> FT767 with no antenna attached). This is strangely, the complete
> opposite I get when operating using the FT767 (i.e. high power at the
> higher end of the audio range).
>
> Has anyone else experienced this,, or has a view on how to address it?
>


Robbie Robertson
 

Sorry to be such a novice, but is that 1600-1700 centered around a particular frequency?

Ghericoan
 

If you are operating at 7070khz, and you feed in an audio tone of 1000hz, the rig will output rf at 7071khz to give you an idea.

The SSB filter operates at AF, but it is relative to where the oscillator is operating. Least thats the best sense I can make of it.

If this reply seems off, I apologize, I am missing emails here and there from this thread.

On Thu, May 24, 2018, 6:17 PM Robbie Robertson <robbie.robertson@...> wrote:
Sorry to be such a novice, but is that 1600-1700 centered around a particular frequency?


--
----------
N5WLF, Greggory (or my nickname, Ghericoan)
General Class, Digital Radio Hobbyist

Ralph Mowery
 

That is the total bandwidth of the filter.

The following is not exact but close enough for me to see what was going on.

I fed an audio signal into the mic input at 1000 Hz.  At 28 Mhz I was getting 5.5 watts out of a modified ubitx using  the better output transistors and several other modifications that have been made by others.

From that point I moved the audio signal up and down to where the power dropped off to about 3.5 watts.

With the bfo set to  11.996.800 mhz the low end was 500 hz and the high end 1900 hz
                               11.996.600               low end was 600 hz and the high end 2100 hz
                               11.996.400                                    400 hz                             1800 hz

If the bfo is moved too close to the filter, the 'carrier' power will go up and reach about 5 to 10 milliwatts output.

de ku4pt


On Thu, May 24, 2018 at 6:17 PM, Robbie Robertson <robbie.robertson@...> wrote:
Sorry to be such a novice, but is that 1600-1700 centered around a particular frequency?
_._,_._,_


Robbie Robertson
 

Many thanks for the help guys (it's much appreciated :o).
I'll have to do some testing on mine, as I didn't think I was seeing a 'curve' in the power out, rather something more linear, with high output at say 500Hz, and steadily decreasing as I move up.
This is probably just my very basic testing, so I'll report back when I've completed a test with small changes.
I guess if there is a sweet spot range, then that's where I'll call CQ...

Robbie G0HYN

John P
 

I haven't been following all the uBitX threads closely, but I believe someone out there has developed software with CAT control. If that is indeed the case, using that can fix your problem.

For FT-8 on my Yaesu FT-891 I use DxCommander to control the radio and WSJT-X for the FT-8 part of things. WSJT allows you to use full-blown split frequency mode or it can "Fake It". In either case, what it does is adjust the transmitter frequency so as to keep the audio signal near the center of the filter. So for example, if I'm transmitting on the 1,500Hz audio slice, it will drop the transmit frequency to 7.0735, which means the filter will be seeing a 1,000 Hz signal.

One of these days, I'll get the uBitX out of the box and put together!
--
John - WA2FZW

Robbie Robertson
 

Thanks John. I too use DxCommander to control my Yaesu FT767 (with WSJT-X), but now I can use CAT directly to the uBITX (sudo FT817).
I'm not familiar with using split frequencies, as I naively thought that at 'the other' end they would rx a different frequency from me than they had original sent on.
So I think your saying that the software/rig can adjust the tx frequency to keep the audio stays in my 'sweet spot', but the receiving station would get the same see my signal in the same spot on their waterfall as they have transmitted on... is that right?

I'll do some reading... :o)

Robbie G0HYN

John P
 

That is correct. And it's not necessary to be on the same slice as the other station. 

--
John - WA2FZW

Robbie Robertson
 

Well, as the old saying goes, 'you learn something new everyday' :o)

Many thanks.

Robbie G0HYN