Returning from Tx in transverter mode

[Roberto48]

Hi,

First: my Portsdown is working great, even on 13cm! Thanks to the designers.

But I have a small problem... When switching back from Tx mode, the transverter LED for that band is burning and DIGITHIN-7 = high. After I select a preset the normal band LED is on again. This behavior is only in MPEG2 mode...
Anyone an Idea?

Thanks!
Rob PA0RWE

[G8GKQ]

Hi Rob

I think that what you are seeing is as designed. The band and transverter select LEDs were supposed to stay on in receive mode so that the correct receive down-converter could be selected. It sounds like you are transmitting in a transverter mode (is the frequency button split with F: xxx T: xxx ?) and then when you select a preset it is switching to a non-transverter band. However, the behaviour should be the same in MPEG-2 as H264....

Sorry, it is quite complicated and confusing. I have tried to explain it here: https://wiki.batc.org.uk/Portsdown_2018 ... _and_Bands

Some photos of the touchscreen and the LEDs would help.

Dave, G8GKQ

[Roberto48]

Hi Dave,

Thanks for reply!

As far as I can see I'm not in transverter mode. I'm using the 8-band decoder and RF-switch.
The strange thing is that this problem was introduced after I build the Portsdown in a nice enclosure. I checked all the connections twice...
I have added 3 photo's so you can see what I mean.
1st: Normal situation 2: In TX mode and 3: return from Tx. As you can see the green LED is lighted.

I did a factory restore but the problem stays.

BTW: there is no difference between H264 and MPEG-2 anymore....

Rob

[G8GKQ]

Hi Rob

I now remember that I've seen something similar to this before. It's a short-circuit or open circuit in the wiring between the RPi and the 8-band switch board. Probably an open-circuit on the line from pin 7 on the RPi.

Dave

[Roberto48]

Hi Dave,

I think I found the problem.. It seems that the T-line not becomes real 0 when in normal mode. When I add a pull-down resistor of 10K between the T-line and ground, the problem is over. Maybe some leakage....

Rob

[G8GKQ]

Hi Rob

I have just reproduced your problem! Investigating now....

Dave

[Roberto48]

OK Dave,

Maybe you have to add a software pull-down for the T - I/O pin.

Good luck!
Rob

[G8GKQ]

Rob

I had seen this problem as a weak glow on the indicator LED that I have on pin 7 on my test rig, but not really thought about it.

Pin 7 has a 50K pull-up by default, and when rpidatv terminates at the end of a "Portsdown", "UGLY" or "DIGITHIN" transmit session, the GPIO is sometimes released because it is used as a clock in "DIGITHIN" mode. This causes it to be pulled high by the 50K and activate the transverter switch.

The perils of shared GPIOs!

I have added a few lines of code to set Pin 7 as an output again at the end of a transmit session, so there may be a brief pulse of pull-up, but with a 10K pull-down this should not be apparent.

The fix will be in the next release (201811300).

Dave

[Roberto48]

Hi Dave,

I understand what is happening! I leave the 10K in place HI!

Thanks for the fix.

Rob PA0RWE