Video Receivers characterization

Stuff I am working on
Post Reply
Daniel Wee
Site Admin
Posts: 2084
Joined: Wed 25 Feb 25 2009 8:00 pm

Video Receivers characterization

Post by Daniel Wee » Tue 10 Aug 10 2010 7:02 pm

I just did a side-by-side comparison between the Lawmate 2.4GHz receiver (which uses ComTech modules), the IF 2.4GHz receiver, a Chinese 2.4GHz video receiver that uses Airwave modules internally, and the Foxtech RC302 2.4GHz receiver. In this test, all were connected to an unmodulated 15mW source through a stepped attenuator chain of 125dB.
Video Receivers 035a.JPG
Video Receivers 035a.JPG (89.14 KiB) Viewed 15841 times
Video Receivers 037a.JPG
Video Receivers 037a.JPG (95.47 KiB) Viewed 15841 times
Video Receivers 036a.JPG
Video Receivers 036a.JPG (85.15 KiB) Viewed 15841 times
Upon initial inspection, it is plain that the RC302 is considerably smaller (and also lighter @43.5g) than all the other units. This may be important for installations which are carried around by the user (such as a belt mounted setup.) The Chinese unit came in a large and heavy steel case that had begun to rust by the time of this testing. Specifications wise:-

Lawmate RX-2460CK
Link: http://www.nghobbies.com/cart/index.php ... ucts_id=92
Nominal operating voltage: 12V
Minimum operating voltage: ~10V
Video Receivers 024a.JPG
Video Receivers 024a.JPG (66.05 KiB) Viewed 15841 times
Video Receivers 025a.JPG
Video Receivers 025a.JPG (64.33 KiB) Viewed 15841 times
(IF) GP-737 (a.k.a. GP-707 - different casing and styling)
Link: http://www.nghobbies.com/cart/index.php ... cts_id=348
Nominal operating voltage: 8V
Minimum operating voltage: ~6.5V
Video Receivers 027a.JPG
Video Receivers 027a.JPG (63.21 KiB) Viewed 15841 times
Video Receivers 029a.JPG
Video Receivers 029a.JPG (60.39 KiB) Viewed 15841 times
Foxtech RC302 (SKY-RX2188)
Link: http://www.foxtechfpv.com/foxtech-24g-8 ... p-182.html
Nominal operating voltage: 12V
Minimum operating voltage: ~6.5V
Video Receivers 022a.JPG
Video Receivers 022a.JPG (73.09 KiB) Viewed 15841 times
Video Receivers 020a.JPG
Video Receivers 020a.JPG (65.75 KiB) Viewed 15841 times
Chinese Airwave (AWM634RX) based receiver
Link: n/a
Nominal operating voltage: 12V
Minimum operating voltage: ~6.5V
Video Receivers 014a.JPG
Video Receivers 014a.JPG (81.66 KiB) Viewed 15841 times
Video Receivers 015a.JPG
Video Receivers 015a.JPG (72.55 KiB) Viewed 15841 times
It would appear that all these receivers perform quite similarly on basic tests, as far as sensitivity go. All go into full-quieting (black screen with no noise) at around -85dBm. This doesn't tell us very much about actual performance, though. For that, we will be doing an actual reception testing with a video transmitter with a standard video feed.

Update: The RC302 receiver has also been tested and the adjacent channel blocking starts around -65dBm. In this regard, the Lawmate receiver is a bit better, with blocking starting around -60dBm.

Daniel

Daniel Wee
Site Admin
Posts: 2084
Joined: Wed 25 Feb 25 2009 8:00 pm

Video Receivers characterization

Post by Daniel Wee » Tue 17 Aug 17 2010 8:52 pm

Video performance testing was done with a very weak RF signal being transmitted from the other room. The measured signal strength at the receiver is between -97dBm to -99dBm. All the receivers were tested using the exact same antenna in the exact same spot (+-1mm). In so far as was possible, everything was kept the same for all tests. Two sets of tests were made on two different days. The first photos of each receiver was from the first day, and the second from the second day. As you can see, there is good repeatability in the results. There was some Wi-Fi interference during the tests so you may want to ignore the Wi-Fi stuff.

On the first day, the test was made using CH2 (2.432MHz) and this favoured the non-Lawmate receivers because it better matched the frequency of the receiver. On the second day, the test was made using CH3 (2.450MHz) and should be equal for all receivers.

Lawmate RX-2460CK (Comtech FM2400RTIM8)
Full-quieting: -85dBm
Detection: -95dBm
Video test:
RX-Lawmate.JPG
RX-Lawmate.JPG (112.2 KiB) Viewed 15834 times
LM2-back2.JPG
LM2-back2.JPG (97.59 KiB) Viewed 15800 times
Foxtech RC302 (SKY-RX2188)
Full-quieting: -85dBm
Detection: -95dBm
Video test:
RX-RC302.JPG
RX-RC302.JPG (70.99 KiB) Viewed 15834 times
RC302-(95-back).JPG
RC302-(95-back).JPG (112.42 KiB) Viewed 15800 times
Unknown make (Airwave AWM634RX)
Full-quieting: -90dBm
Detection: -100dBm
Video test:
RX-Airwave2.JPG
RX-Airwave2.JPG (94.76 KiB) Viewed 15834 times
AW-(95-back).JPG
AW-(95-back).JPG (101.08 KiB) Viewed 15800 times
GP-737 (Goscam GP622R)
Full-quieting: -85dBm
Detection: -95dBm
Video test:
RX-GP737-2.JPG
RX-GP737-2.JPG (107.88 KiB) Viewed 15834 times
GP-(95-back).JPG
GP-(95-back).JPG (104.19 KiB) Viewed 15800 times
Daniel
Attachments
SKY-RX2188.pdf
(890.81 KiB) Downloaded 576 times
GOSCAM-17_33_1185610763.pdf
(1005.94 KiB) Downloaded 540 times
Comtech-fm2400rtim8.pdf
(540.68 KiB) Downloaded 530 times
Airwave-AWM634RX.pdf
(91.63 KiB) Downloaded 471 times

Daniel Wee
Site Admin
Posts: 2084
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: Video Receivers characterization

Post by Daniel Wee » Wed 18 Aug 18 2010 6:16 pm

Lawmate RX-2460CK (Comtech FM2400RTIM8)

This very popular receiver has been the workhorse receiver for 2.4GHz FPV and has been around for a long time. It is the biggest among the receivers tested and sells for around USD50 (NGHobbies) under various labels. It draws a hefty 240mA and runs pretty hot, mainly because it contains not one, but two, linear regulators - one of which is a 7809. This means that you cannot go lower than about 10V with the supply before the 7809 output starts to sag.

Frequency table:-
  • CH1 - 2410 MHz
    CH2 - 2430 MHz
    CH3 - 2450 MHz
    CH4 - 2470 MHz
    CH5 - 2370 MHz
    CH6 - 2390 MHz
    CH7 - 2490 MHz
    CH8 - 2510 MHz
*note: Older Lawmate receivers may have slightly different channel assignments

The receiver itself puts up a decent performance, with good adjacent channel blocking at around -60dBm. You can get a noisy image at -95dBm and a full-quieting image at -85dBm. Generally speaking, this is a tried and tested receiver and you probably can't go wrong with this for 2.4GHz operation. I modified mine and replaced the 5V linear regulator with a switching one to cut down on the heat dissipation.

It has been rumoured that Lawmate is getting out of the 2.4GHz business so this receiver may not be available for very much longer. It retails for around USD50 (NGHobbies) at the time of this review.

(IF) GP-737 (a.k.a. GP-707)

Frequency table:-
  • CH1 - 2414 MHz
    CH2 - 2432 MHz
    CH3 - 2450 MHz
    CH4 - 2468 MHz
Foxtech RC302 (SKY-RX2188)

Frequency table:-
  • CH1 - 2414 MHz
    CH2 - 2432 MHz
    CH3 - 2450 MHz
    CH4 - 2468 MHz
    CH5 - 2370 MHz
    CH6 - 2390 MHz
    CH7 - 2490 MHz
    CH8 - 2510 MHz
Summary of findings (tentative)

After extensive testing, it would appear that the RC302 performance is somewhat lacking, even though the module datasheet suggests a -90dBm sensitivity. The GP-737 (GP-707) receiver seems to be putting through a very respectable performance.

The Lawmate exhibits better adjacent channel rejection and this may help when using the receivers in a multi-frequency usage type of setting (where you have more than one 2.4GHz video channel in use). In most cases, this can be mitigated by careful selection of channels (avoiding adjacent channels).

All of the receivers contain linear regulators and have a tendency to get very hot during usage. This is especially so with the Lawmate receiver because it contains two linear regulators and thus gets hotter than the other two.

At the end of the day, I would say that the GP-737 is closely tied with the Lawmate for the best sensitivity performance, edging out the Lawmate by a hair. It also exhibits better colour saturation and has lower heat dissipation. Unfortunately, it only offers four channels and of the four, only CH3 is perfectly matched to the Lawmate transmitter frequencies - something to consider if you are using a Lawmate VTX. This is then followed by the Chinese receiver (using Airwave modules, and notwithstanding an apparently better tested sensitivity) and lastly by the RC302. The Airwave module does have nice saturation but the video signal is a little odd, losing lock quite easily.

Halfway through testing, the RC302 video output became very dark for some reason. The signal was still being received correctly but the video output stage may have developed a problem in the module itself. I was unable to fix this easily.
RC3022-back.JPG
RC3022-back.JPG (22.73 KiB) Viewed 15800 times
As much as I liked the small profile of the RC302 receiver, it looks like it may be lacking in some crucial areas of performance and reliability. The fact that it uses RP-SMA instead of regular SMA connectors may also be an important consideration for some.

update: Replacing the two output transistors on the RC302 fixed the problem with the darkened output. Stuff looks okay now.

For now - the GP-737 is best if you can live with the channel selection, or the Lawmate 2.4GHz receiver would be a safe bet but expect the colours to be a bit more washed out (less saturated.)

Daniel

Daniel Wee
Site Admin
Posts: 2084
Joined: Wed 25 Feb 25 2009 8:00 pm

Re: Video Receivers characterization

Post by Daniel Wee » Tue 24 Aug 24 2010 5:58 pm

Re-testing the RC302

Because of the output issue with the RC302, I decided to open it up and get it fixed. This involved replacing both the output transistors. In the process, I took pains to clean up what looked like residual flux/solder-paste on the board, with methylated alcohol. After this I checked that the output was now functional again and so I decided to make a quick test to see if the overall performance has changed.

RC302
RC302-7-(back)2.JPG
RC302-7-(back)2.JPG (91.91 KiB) Viewed 15791 times
GP-737
GP-7-(back)4.JPG
GP-7-(back)4.JPG (119.17 KiB) Viewed 15791 times
Lawmate
LM-7-(back).JPG
LM-7-(back).JPG (99.24 KiB) Viewed 15791 times
In this repeat test, you can see again that the GP-737 and the Lawmate are neck-and-neck in the shoot-out, but the RC302 lags behind somewhat. With just a bit stronger signal, the RC302 performs quite well. I should also mention that for some strange reason, the RC302 performs better with the input voltage around 5.5V (resulting in about 3.3V to the module). The datasheet for the module allows for an operating voltage up to 5.5V so it really should not make any difference but the colour noise seems to be slightly lower when operated at lower voltages.

Daniel

Post Reply