Antenna Referred Power Measurement.

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rob2396
Posts: 5
Joined: Fri Dec 16, 2016 7:11 pm

Antenna Referred Power Measurement.

Postby rob2396 » Fri Dec 16, 2016 7:51 pm

Hi all
If you place your mouse cursor over the signal level in the main frequency display of the Receiver Panel (RX) of my RSP1 it displays "Antenna Referred Power Measurement".

Question: What does this mean as I can not find Antenna Referred Power anywhere? Or is this a colloquialism from the USA?

Thanks Rob
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DanubeBCL
Posts: 168
Joined: Sat Jul 02, 2016 12:39 pm

Re: Antenna Referred Power Measurement.

Postby DanubeBCL » Sat Dec 17, 2016 10:55 am

dBm is a power measurement unit (power in relation to 1 milliwatt). In radios the power normally is calculated from the voltage on the 50 Ohms antenna input. Maybe the "creator" of this expression wanted to express all this in one term. But I also think the expression is not very meaningful.
In SDR software/radio combinations where you can "create" almost any dBm (and S meter) value by gain and AGC adjustment I think a dBm value is pretty useless. It is just a lottery number for relative assessments, but not for exact measuring. It pretends accuracy, but there is none. SDR receivers where the dBm values really reflect the power at the 50 Ohms input (e. g. Perseus, Winradio G3xDDC, PowerSDR/Angelia and others) play in a different league.
73s, Heinrich

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rob2396
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Joined: Fri Dec 16, 2016 7:11 pm

Re: Antenna Referred Power Measurement.

Postby rob2396 » Sat Dec 17, 2016 11:35 am

Danube Bcl
Thank you for the very concise reply. I agree with you the expression used is unfortunate, perhaps a more applicable definition might be in order or not to use one at all. Thanks again.

Regards

Rob2396
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dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: Antenna Referred Power Measurement.

Postby dsalomon » Sat Dec 17, 2016 2:35 pm

DanubeBCL's post makes me wonder about something. The other SDRs he mentioned that "play in another league" do so mainly because they sample the signal at a much higher rate and with more bits. I have a NetSDR, and a WinRadioG33DDC, which have 16-bit, 122msps and 16-bit 100msps ADCs, respectively. Comparing them to other SDRs that I have with 12, or even 8 bit architectures (i.e. some RTL SDRs) one really can see the different league they play in.

So, what makes me curious is - are there SDRs either currently in production, or being developed with even better ADCs than the current crop of SDRs? The best specs I am aware of in CURRENT SDRs are 370msps / 16-bit ADCs. The Crimson TNG from Per-Vices has "four independent receive chains" with ADC specs of 370msps / 16-bits. That's 3 TIMES as fast as the fastest ADC in any other SDR that I've seen. Here's their main website: http://www.pervices.com/. The cost, a mere $14,500. Yikes! :o So, that's definitely in another league from the current crop, and the price is also in another league. Has anyone done any side-by-side performance comparisons of this against other SDRs. Does anyone know of any other SDRs, current or in development with ADCs that exceed 122msps / 16-bit, but are not quite at the Crimson TNG level? Is there a smaller step up from the current top tier?

Best regards - David

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DanubeBCL
Posts: 168
Joined: Sat Jul 02, 2016 12:39 pm

Re: Antenna Referred Power Measurement.

Postby DanubeBCL » Sat Dec 17, 2016 6:42 pm

Well David, there are certainly "better" SDRs with higher direct sampling rates and so on, but I have given up to look for new SDR receivers. The ones I own (Perseus, G33DDC, Anan Angelia, apart from the toys like Funcube, RSP1 or RTL dongles) were expensive enough and it makes no sense for me to hunt for new equipment.
The local RF noise situation here has become so bad over the last 3 or 4 years (mainly by the European plague homeplug powerline PLC modems) that every high quality receiver is money thrown out of the window (for me). Only a remote receiver somewhere in the quiet countryside could play with its muscles. But this is far away from reality for me.
I just wanted to comment that the dBm "measurement" in SDRuno/RSP is to be treated with care unless it's garanteed that it is calibrated. But just move the gain slider in SDRuno and you can see any phantasy result. I do not critisize this, because one must take the budget price into account and should not expect a precise RF gear like a Rhode & Schwarz or something.
73s, Heinrich

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dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: Antenna Referred Power Measurement.

Postby dsalomon » Sun Dec 18, 2016 3:22 pm

DanubeBCL -

I agree with your comments re: measurements. The only measurements I trust are Sherwoods. He's measured and writeen up a few of the SDRs, although I don't recall which ones at the moment. He came up with a measurement that fairly measures them and that the manufacturers cannot fudge (although I cannot recall that either off the top of my head - getting old, can't remember stuff anymore :-). There's another guy, Adam Farson / AB4OJ, who is also very technically competent and has done SDR testing on a number of radios, producing some interesting papers on the results. He's got a page (http://www.ab4oj.com/test/main.html) with some great links to radio testing and measurement educational and reference materials. Here's a link to his page listing the SDRs (and other radios) he's tested: http://www.ab4oj.com/test/reports.html.

Re: the noise, sorry to hear about the use of the powerline devices. They were tried here in the US and, thankfully beaten into submission for various reasons. I recall that the ARRL fought hard against federal support for funding for that technology. There are times that we here in the US who are ARRL members whine and complain about our membership money being wasted. However, when something BIG comes along, like powerline, they do a great job going to bat for the amateur community to try to avoid thing that are bad for radio. When we fight the government about taking away our space, or allowing a technology that clearly causes RFI, we always fall back on the good that amateur radio does for the community, especially in times of emergency. It's the only card we have to play.

Anyway, I digress. Perhaps you can find someone who lives out in the country somewhere to host your radios, PC and an antenna? Your comment got me thinking about that. I live in a small town that's been growing very, very quickly over the past few years and even though it's still a pretty small town, the growth has definitely caused RFI growth as well. Simon Brown recently (well, within the last year or so) moved from Switzerland back to the UK, but he's still in the country. I know he's got antennas...lots of antennas. I wonder if he would consider being a host for some SDRs. I might put together a proposal to him. Something like, we pay for all the associated costs (i.e. a PC, battery backup, a receive only antenna, a percentage of his internet costs), plus a little extra each month to give him some incentive to be a host. By "we", I mean anyone I can find who might be interested in something like this. In exchange, he finds a quiet corner in his house to connect everything up. We would control and maintain everything remotely. So all he would have to do, besides the initial hookup, are things like disconnect antennas, PCs and radios during storms (which I assume he does anyway) and anything else that could not be done remotely. I've done remote PC support for people for many years, so I know it can be done and it's not terribly difficult to set up. Hmmm, gotta think some more about this...

Best regards - David

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someYguy
Posts: 46
Joined: Sun Apr 10, 2016 7:12 pm

Re: Antenna Referred Power Measurement.

Postby someYguy » Mon Dec 19, 2016 10:01 pm

Actually, the latest version of SDRuno does seem to have very good automatic & accurate power measurement figures, and you can easily calibrate HDSDR, SDRSharp, and SDR Console to do same.

I have used the RSP1 as a test device and found it to be both sensitive and accurate once calibrated. To calibrate, I use a signal of known strength from a calibrated HP model 8656B RF signal generator. For measurements, I usually calibrate to a reference line of -30dbm at the top of the screen. I do this by disabling both the LNA and the AGC in the RSP Device Control Panel. Gain Reduction is set manually to achieve calibration to the -30dbm reference signal. At present, SDRSharp seems to be best software for this.

Using this method, I've found the RSP1 to be quite linear and accurate across the power measurement range of -120dbm to -20dbm. If higher input levels are to be measured, I use a calibrated step attenuator at the RSP1 input and simply subtract the value.

I also have checked this setup against a known calibrated Instek model GSP-810 spectrum analyzer and the two agree to within < 1dbm.

This is for basic signal and power measurement, but the RSP1 can also be used as test equipment for much more, such as antenna analysis, etc.

If interested, see my post here: http://www.sdrplay.com/community/viewtopic.php?f=7&t=1562

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DanubeBCL
Posts: 168
Joined: Sat Jul 02, 2016 12:39 pm

Re: Antenna Referred Power Measurement.

Postby DanubeBCL » Tue Dec 20, 2016 10:49 am

To David,
to avoid being off topic too much I try a short answer: In Europe the powerline modems (PLT, PLC, dLAN, powerLAN etc.) have been generously allowed at high noise levels due to intensive "work" of the industry lobbyists at the European Parliament, using up to 105 dBµV broadband power on unshielded power lines in the houses. They mean practically the death of any reception between 1.6 and 78 MHz except for the ham radio bands which they statically notch after heavy protests. The most heard argument of the politicians was: Nobody needs shortwave radios any more.
73, Heinrich

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LulaNord
Posts: 1
Joined: Wed May 31, 2017 6:45 pm

Re: Antenna Referred Power Measurement.

Postby LulaNord » Wed May 31, 2017 6:51 pm

Hi...i am a new user here. As per my knowledge in radios the power normally is calculated from the voltage on the 50 Ohms antenna input. Maybe the "creator" of this expression wanted to express all this in one term. But I also think the expression is not very meaningful.

assembly circuit

JMG
Posts: 16
Joined: Thu Mar 26, 2015 9:58 pm

Re: Antenna Referred Power Measurement.

Postby JMG » Thu Jun 01, 2017 8:14 am

"dBm" makes a lot of sense! DBm is a logarithmic parameter for rf-power, not depending on the impedance.

In the near future it will replace all the last century parameters like dBuV, S-units, receiver sensitivity uV, power....
All modern test equipment like signal-generators, power sources, power meters, spectrum analysers, etc. they all rely on dBm already.

The dBm value of the RSP receivers is the absolute, real RMS power at the receiver input, measured within the IF channel. It is a unique feature which can not be found at any other SDR unit! It allows the receiver to be used as a precise tool to measure rf power over a frequency range of 10kHz...2GHz. The accuracy has been found to be within +/-0.5dB within the most settings. Amacing.

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