84 replies to this topic

[Mr.RC-Cam]

There have been discussions in the past about reading the signal strength (RSSI) pin that is inside many popular wireless video receivers. It's a simple hack for adding a signal strength readout. Using the RSSI is nice tool to compare antenna performance, avoid signal loss during use, optimize antenna installations, and so on. As mentioned before, a voltmeter can be used, but reading voltages is not very intuitive.

So I upgraded a previous design and used a nice numeric LCD display. The RSSI voltage is converted to a 0-100% value (0= no RF signal, 100 = full RF signal). A percent value is so much easier on the eyes than the raw RSSI voltage.

Here's the front view of the prototype:


Here's the back view. The lower left shows a hidden calibrate push switch. That is to say, because every receiver is different, there is a built-in utility that automatically calibrates things for a 0-100% range.


Here it is wired to a typical 900Mhz Rx (three wires: Power, Gnd, RSSI).


This is NOT a open source project since I am considering commercializing it later this year. But if there is any interest in it now, I can have some made for a special forum member purchase. Like some of my past specials, it would be a discounted price and limited to *registered* rc-cam forum members. Target price for this deal will be around $25-$30. If interested, then post your "I want one" in this thread (please do NOT email or PM me). If there is enough takers I'll get some built later this month.

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Edited by Mr.RC-Cam, 02 June 2010 - 08:34 AM.

[mrfliboy]

I want one!!

[Mr.RC-Cam]

Good to see a "I want one." While we wait for more interest to appear, here is the preliminary instruction manual that describes the installation.

 rssi_instructions.pdf   185.59K   733 downloads

[mrfliboy]

Instructions look great.

Edited by mrfliboy, 03 May 2010 - 03:28 PM.

[Kilrah]

I want 4, but need to check about RSSI in my new RXs first

[Terry]

Thats something I have been wanting to add for a long time but never get round to it, if they work on your 5.8Ghz RX's then I will have 2 for now.

Terry

[Mr.RC-Cam]

if they work on your 5.8Ghz RX's then I will have 2 for now.

I've tested it on the dpcav 5.8GHz Rx and compared a 100mW Tx with the 500mW 5.8GHz proto Tx. As expected, the RSSI readings easily showed the stronger signal.

I ordered the solder paste stencil today and I expect it in a couple weeks. I'll keep this member-only invitation open for a few more days, then it will be closed down and parts will be ordered. Once I have the paste stencil I will be able to get the boards assembled.

[Old Man Mike]

I've tested it on the dpcav 5.8GHz Rx and compared a 100mW Tx with the 500mW 5.8GHz proto Tx. As expected, the RSSI readings easily showed the stronger signal.

I ordered the solder paste stencil today and I expect it in a couple weeks. Once I have the paste stencil I will be able to get the boards assembled.

This will be a nice device to help tune up RF systems. After doing a similar design integrated into an OSD, I'll offer a caution note about the AGC sensitivity to temperature. At least for Lawmate units, the AGC will read about 10 dB higher in it's aprox 45 dB measurement range at initial turn on compared to a warm unit 30 mins later. You can imagine how this could confuse someone attempting to compare performance. Also note that since the AGC is a very non-linear output, showing a percentage could be a bit misleading. Here is a typical AGC response for the Lawmate:



(Bottom of scale is A/D output where 800 is aprox 4 volts)

I had to use the six linear scaled segments in the processing to get reasonable accuracy of measurements.

Finally to complicated things a bit more, most of the the Chinese units have a reversed AGC curve where the strongest signal produces the lowest voltage which you can see is the opposite response of the Lawmate.

Just thought this info might be helpful.

OMM

[Mr.RC-Cam]

Thanks for sharing the dB scaling data, it's all great stuff to discuss. I too have observed the RSSI curve performance on many different A/V receivers and I can confirm that they are non-linear, temperature drift, and their dB scaling varies substantially from Rx to Rx. For sure, precision instrument makers like HP and TekTronix do not need to worry about competition from nifty measuring system hacks like this. But having used RSSI for a variety of testing in the past, I can say that it is a useful and affordable way to make RF comparison measurements. The alternatives can cost as much as a nice luxury car.

Good point regarding the reversed scaling on the Chinese Rx's. It is handled by the calibration feature built into the meter. It is smart enough to recognize the RSSI's slope polarity and dynamic range. In the end, it's just a bit of software magic.

[Midwest-Flyer]

I want one

[Old Man Mike]

...
Good point regarding the reversed scaling on the Chinese Rx's. It is handled by the calibration feature built into the meter. It is smart enough to recognize the RSSI's slope polarity and dynamic range. In the end, it's just a bit of software magic.

Nice work! I wondered if you went that extra step in the software. I like to support fine engineering so please sign me up for one.

OMM

[Devonian]

I want one - well, 2 actually.

If possible, to keep shipping reasonable, could we organise one person in the UK to receive all for UK people and then re-distribute them? (re-posting cost to be covered of course).

Nigel.

[Mr.RC-Cam]

If possible, to keep shipping reasonable, could we organise one person in the UK to receive all for UK people and then re-distribute them? (re-posting cost to be covered of course).

It would be less work for me, so you have my vote. However, the expected international shipping cost should be low enough to make the effort unnecessary. Please mention the group shipment idea again when I get close to shipping the meters.

[Terry]

Knowing the cost of duty and shipping I think sending direct would be less risky.

Terry

[galaxiex]

Very nice! I want one. maybe even 4 of them....

Edited by galaxiex, 07 May 2010 - 04:53 AM.

[Devonian]

Knowing the cost of duty and shipping I think sending direct would be less risky.

Terry

Sad but true.

I'd like mine marked as 'gift'

Nigel.

[masam]

Yes, I want one. Hopefully the cost of shipping is not too much.

[Flyonlion]

Oh yeah I WANT ONE

[Mr.RC-Cam]

The solder paste stencil is fabricated. That means RSSI board assembly will begin in a couple days. All payments will need to be handled by PayPal (sorry, but no other payment methods are available for this special deal).

But before we settle the payments, let's confirm the "I want one" counts:

mrfliboy: 1 (SHIPPED MAY 19)
Kirah: 4 (SHIPPED MAY 20)
Terry: 2 (SHIPPED MAY 19)
Midwest Flyer: 1 (SHIPPED MAY 22)
Old Man Mike: 1 (SHIPPED MAY 21)
galaxiex: 1 (SHIPPED MAY 20)
Devonian: 2 (SHIPPED MAY 19)
masam: 1 (SHIPPED MAY 20)
Flyonlion: 1 (SHIPPED MAY 21)
Sebastian: 4 (SHIPPED MAY 19)
andrei: 1 (SHIPPED MAY 21)
kist2001: 2 (SHIPPED MAY 25)

If your name is missing, or you need to change your quantity, then post the details in this thread BEFORE May 15.

Edited by Mr.RC-Cam, 02 June 2010 - 08:34 AM.
Updated shipped info

[Terry]

No 2 for now pls

Terry