Improving PlayTV reception Part 2

So it turns out that my PlayTV stuttering issues are probably not linked to signal strength, having verified the aerial (new), cabling (RG6) and signal strength reported by 2 other digital receivers as very high (one reports 100%). During tuning, PlayTV seems to briefly indicate 100% also. It's not the HDD (off during live TV) and I've tried 720p and 1080i output with no difference.

But no matter - I'll wait for poor weather to test if an amp makes the difference.

The following setup shows what I've tried with a 5V masthead amp and it doesn't seem to make things worse at least, with or without 5V injection from 2nd USB port.

So because I don't have a DTV spectrum analyser, I'm just going to assume the masthead amp is doing something here. Certainly I see the signal input on the PlayTV jump to +5V potential in the above scenario, but can't determine the nature of the AC (MHz). I'll have to wait for some more testing.

Onboard Power

This is the ultimate goal - powering the amp from PlayTV. On the PCB there seems to be 1.9V and 3.3V rails (see comments on previous post - thanks Rowan). Finally I found the voltage divider - an IC indicated in the image with pin configuration below.

5V   __.___.__  3.3V
       |   |
Gnd  __|   |
       |   |
1.9V __|___|__  1.2V

So basically I need to either tap the mini-USB jack directly or the pin above to power the aerial signal (see marked solder point).

Dissecting the PS3 PlayTV for Poor Reception

I recently purchased a PlayTV (see here also) and am fairly happy with it (many software improvements could be made - see later) but I'm having previously unencountered reception problems. It would seem I'm not alone and have even spoken to friends worse off than me where they have a working STB, but can not even use the purchased PlayTV due to weak signal.

In my case, whereas my old Sony DVR is able to receive all channels perfectly, the PlayTV breaks up and skips, mainly on ABC/ABC2. I'm no expert, but put this down to a cheap design without pre-amplification.

I had a thought; with USB connected to the unit (and therefore 5V +/- 0.25 and capability to deliver 500mA), why not devise a simple in line amplification solution drawing on no external power source? Sure I can buy a cots distribution amplifier, but yet another power pack when USB is available?

Time then to investigate the PlayTV PCB. Here's the front:

and here's the back, flipped for convenience:

I'm not an electronic engineer and know little more than basic electrical theory, but the first thing apparent to me is that the board uses contacts 2/3 only (USB data) and does not use the 5V bus power (contact 1).

That is, from the micro USB spec:
1 VBUS Red
2 D- White
3 D+ Green
4 ID <Ra_PLUG_ID
5 GND Black
Shell Shield Drain Wire

Not knowing anything about USB, I can only guess power for the USB and DVB circuitry is drawn directly from data signal itself (order of a few hundred millivots on/off depending) and assume likewise the LED is powered by some sort of rectification of this.

So far so good then - 5V seems available for use. After some further research, it seems that some STBs have the ability to inject the source coax with 5V DC to power an upstream masthead amplifier. Such an amplifier is shown here. I have ordered one and now just need to figure out how to solder onto that tiny tiny 5V rail. Any tips are welcome. Also, without a schematic, I'm not sure of the implications of placing an additional 5V DC onto the DTV signal. I presume however that with other types of masthead amplifiers being common fare, this is not doing anything unusual.

Who are you to dismiss the method?

Now individual political beliefs aside, this is a new level of unprincipled politics even for...well...politicians.

http://www.news.com.au/story/0,27574,26424610-2,00.html

Tony Abbott has said time and again on the record that he doesn't believe in man-made global warming, despite all the evidence from IPCC around reduced Antarctic ice sheets, rising sea levels and rising atmospheric CO2 concentrations. He intends to sink the government's CPRS in this private belief - a scheme that developed bipartisanly under the Howard govt with questionable watering down made during now-laughable "good faith" bargaining from the Libs.

In fact it's been said they got everything they asked for - ammendments I think giving us even less reason to untar ourselves as the per-capita highest carbon emitter in the world. The later we act, the more expensive it becomes and surely the more reliant we become upon imported technology as a result. ABC Business Reporter Adam Kholer's comments last night - we pay more now for not acting upon Kyoto a decade ago.

Ok my point (which I promised was not to be political) - make no mistake that these anthropogenic climate change skeptics (and there are a fair few of them) dismiss nothing less than centuries of progress in my field of establishing a scientific method based on informed hypothesis, empirical evidence, rigorous testing and peer review. This method matured through onslaughts from the same sorts of people that once found their political home within an oppressive Church at a time whence it was more convenient to incarcerate or even execute scientists than face up to threats to personal belief systems or accumulated wealth.

So yes, same shit, different century. But does anyone not see the irony that even these people and their schoolboy trust funds get it, yet a great many people in Australia's second largest political party just can't?

If you want to read the IPCC summary for yourself, it is here. Vote with your conscience.

http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf