Power Meter for DTV using Arduino

Hi all,

My project is about making an antenna rotator for the self-made UHF Digital TV antenna.

The main concern right now is the sampling of the DTV signal received from the UHF antenna (estimating at 400 - 700MHz). What I needed is just the power level of the received antenna, the unit of the output does not matter, as long as the magnitude is increased/decreased based on the performance with the 5v reference from the Arduino of the received signal so that the rotator can rotate accordingly.

I had look through the LT5534 RF Power Detector and it seemed promising, however it is only suitable with 50ohm output, and I am using 75Ohm Coax Cable, does not seemed feasible.

Is there anyway where I can feed the received signal from the Antenna into my Arduino so that I can measure its performance? With it I will only be able to rotate my antenna accordingly.

Thank you very much.

Is there anyway where I can feed the received signal from the Antenna into my Arduino so that I can measure its performance?

No.

Digital TV is different from analogue TV in that their is no carrier to use as a base level for received signal strength. Anything you measure with a power meter will change depending on the picture content of several stations being transmitted in the multiplex, or "mux" as it is know in the trade.

I had look through the LT5534 RF Power Detector and it seemed promising, however it is only suitable with 50ohm output, and I am using 75Ohm Coax Cable, does not seemed feasible.

I think that shows you how little you know about the subject. The mismatch of 50 ohm and 75 ohm is not very much and would not affect the relative reading. However as I just explained it it totally unsuitable for measuring power in a DTV system.

Made once an analogue TV signal strength meter (40+ years ago), and it was not easy.
Analogue TV has a suppressed main carrier, so bulk signal is varying a lot with picture info.
If I remember right, I had to measure/sample during the no-picture (sync) part of the signal.

Digital TV might be easier to measure than analogue TV, since it has multiple carriers per TV channel, and multiple TV channels per UHF channel block. Seems to be a total of 6817 carriers per block.

I suppose you need to use a splitter to feed the aerial signal simultaniously to the TV and measuring device.
Don’t know if that chip is sensitive enough for an aerial signal. You might need a booster in front of the chip.
Mismatch should indeed not be a problem.

Maybe better to make an accurate positioning system for your rotator, so it goes to the exact same position every time.
Leo…

https://www.jaycar.co.nz/digital-tv-signal-strength-meter/p/LT3332
https://www.ebay.com/p/95dtw-Dvb-t-Finder-Digital-Aerial-TV-Antenna-Signal-Strength-Meter-Practical/3006868825?iid=272856150246

Digital TV might be easier to measure than analogue TV, since it has multiple carriers per TV channel, and multiple TV channels per UHF channel block. Seems to be a total of 6817 carriers per block.

Sorry no. It is not that simple, those carriers are not constant signals like old analogue TV, read technical description of a DVB-T transmitter
The original DT TV used a 2K carrier system where as now their are some 8K systems as well in the UK.

Analogue TV has a suppressed main carrier,

Yes but it is present, it also has a vestigial sideband. What mattered was if the modulation was positive or negitave. The old 405 line system was positive modulation where the lowest RF power was transmitted in the sync pulses. The 625 line system that replaced it had negitave modulation where peak RF power was transmitted on the sync signals. This stopped the old 405 problem of picture roll on a weak signal. But this made measurements of received power easier, as the peak signal was constant.

for the self-made UHF Digital TV antenna.

Their is no difference between an analogue TV antenna and a digital TV antenna, they are the same thing.

Grumpy_Mike:
No.

Digital TV is different from analogue TV in that their is no carrier to use as a base level for received signal strength. Anything you measure with a power meter will change depending on the picture content of several stations being transmitted in the multiplex, or "mux" as it is know in the trade.
I think that shows you how little you know about the subject. The mismatch of 50 ohm and 75 ohm is not very much and would not affect the relative reading. However as I just explained it it totally unsuitable for measuring power in a DTV system.

Thank you very much for your input. Yes you are right, I got assigned with this project with almost no prior knowledge to it and I am now struggling trying to make this work.

If power is not suitable as my relative parameter to track the transmitting station, is there any alternative that I can turn to? It doesn't needs to be very accurate as long as the Arduino have a relative base to be referencing at.

Thank you very much.

One digital terrestial block containing several digital TV channels with thousands of carriers must be like random noise. I suspect that the signal strength meters I linked to are just a wideband (not tuned) amp with envelope detector. Maybe best to buy one, and crack it open.
Leo..

What commercial systems do is to in effect act like a set top box and decode the signal. Then from the demodulator you can get two vital measurements. One is signal strength but that alone is not enough to enable you to point an antenna. The other is signal quality a number given by the bit error rate. You see their is a lot of error correction going on in a digital TV transmitter and you do not notice any change in picture quality until it all falls in a heap. However if you look at how hard the error correction is working you can see how close to the edge your are. This is the real parameter you need to look at when pointing an antenna. Many times the maximum signal strength does not coincide with the minimum bit error rate or more likely the frame error rate know by the Farther Ted esque abbreviation of FEC, C for correction.

This leads you to a problem as DTV decoders are some what hard to get hold of. You have great difficulty even getting a data sheet and many times you have to sign a none disclosure agreement befor you can even look at one, let alone buy a chip. This is why commercial signal “strength” meters can cost upwards of £700.

Which means, I do not have the slightest chance for me to realize this project, even with the envelope detector that Wawa had suggested before? This is bad as my degree's on the stake for this thing.

Can't you use one of those cheap USB SDR digital TV devices and get the BER out?

You said the project was for an antenna rotator.
I think that block (or blocks) reception strength is more important than single channel data quality,
which can also be affected by other things like mutipath reception.
As said, buy one of those cheap meters I linked to, and try it or pull it apart.
Leo..

AWOL:
Can't you use one of those cheap USB SDR digital TV devices and get the BER out?

Thanks for the input, I've just looked through it. As far as I could understand, it is able to analyze BER and signal strength via the SDR software, but would I be able to extract the data out and send it to Arduino? That would be the crucial part, as my project is about having the rotator to allign itself automatically, rather than manually using the real-time data given by the SDR software sent into the Arduino.

Wawa:
You said the project was for an antenna rotator.
I think that block (or blocks) reception strength is more important than single channel data quality,
which can also be affected by other things like mutipath reception.
As said, buy one of those cheap meters I linked to, and try it or pull it apart.
Leo..

I guess I could have a try on that, or using the LT5534 chip I've mentioned earlier.

VHao:
This is bad as my degree's on the stake for this thing.

No it is not. A lot of students think that a project has to work in order to pass or indeed get a good mark, this is not the case. For 21 years I was a University Senior Lecturer and I have supervised countless projects. What we are looking for is not if a project is completed but how you go about it. What you have learned so far will be written up into your project. Then go back to your supervisor with these facts and ask for advice as to what direction they want you to take your project in.

Explain how a chip like the LT5534 is not suitable for the right reasons, not the spurious impedance matching bit. Incidentally that makes me think it is not an Electronics degree you are doing or you would have known that already.

Your supervisor might want you to test the chip's performance anyway or take a different approach. For example the locations of all the DTT transmitters are known and for all intents and purposes fixed. These could be pre programmed into your rotator and these known locations tried.

Or you could research commercial antenna pointing aids maybe even get one bought for you for your project, I know their is a lot more money in the UK University system than their was when I was there.

but would I be able to extract the data out and send it to Arduino?

I would doubt it, but if you could coax it to spit out the diagnostic page in a HTML web format maybe you could.

Just had a look at the menu of my Samsung TV, and it has a signal strength and a BER bar.
The BER bar is at zero, and the signal strength is at 97%.

Could be that the aerial direction has to be really off before the BER bar shows errors.
My guess is that signal strength is a better source of information to turn an aerial rotator (smaller window).
Leo..

My guess is that signal strength is a better source of information to turn an aerial rotator (smaller window).

Your guess is wrong.

I designed the digital set top box that OnDigital gave away with their subscription in the early 2000s. What is your DTTV experence?

Signal strength was an issue so as not to interfere with analogue TV. What is important is the reflections in any situation. In an ideal receiver location then yes you tune for maximum signal strength but many locations are not ideal. A good installer will install the antenna for minimum BER while trying to maximize the signal strength. However their were many crap installers.

Note that this signal strength is only available from the demodulator not the RF front end. The signals for DTV are about 60dBs down on what an equivalent analogue TV would be.

A DTV signal is pretty much a block of what looks like noise at more or less full amplitude containing many channels.

  • see 'the art of electronics'

Something like a AD8314 would detect it .

Allan

Thank you everyone for the input, for now I'll consult my supervisor on our upcoming meeting and see what will be the outcome.