Jim "spam filter" Bartell
Edited by JimBartell, 09 August 2007 - 11:39 AM.
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New Video Transmitter
10 replies to this topic
Posted 17 August 2007 - 07:40 AM
I doubt that unit gives a reliable reception on the receiver side, as the modulation they use has easy distortion from reflections of the walls in a studio or any other room.
Posted 17 August 2007 - 08:46 AM
Hi Marc: I'm unable to find any documentation that specifies what form of modulation the Modulus is using; did you find it somewhere or is this something you know via experience / conversation with CIT?
Also, on what basis, fact or exerience are you concluding that AM in short range applications would be any more reflective or "distorted" as you put it than FM, CW, DSB or SSB forms of modulation? How would reflectivity distort an AM signal or are you saying that the receiver end of the equation would not be able to properly decode a scattered or multipathed AM signal the same as say an FM receiver?
Reflectivity and absorbtion has more to do with the frequency; lower frequencies being better able to to penetrate solid objects and higher frequencies being more easily scattered and absorbed.
Edited by Robert Starling, 17 August 2007 - 08:47 AM.
Posted 17 August 2007 - 08:51 AM
Mmmh something has catched my eye. Read this quote from the description: "The newest video sender GX-68 has been designed for steadicam users or professionals." OR professionals. So, we are no pros or what! ;-)
It actually doesn't look really stable and isn't legal for use here in Western Europe anyway.
Thanks for the spam, Jim ;-)
Posted 22 August 2007 - 05:22 AM
I have been trying multiple units the last years (my background is electronics design).
The better transmition/receiving is through diversity receivers other then with single antenna's.
The diversity receivers can't reliable receive standard FM video transmition as the bandwidth and therefore the frequencies of FM very too much to catch the best signal. Even on both antenna's.
Adding more power to the transmitter-part even made it worse, as the reflections became bigger too, suppressing the original signal further. I tested and modified units from 60mW upto 1.5W. The more power only has only advantages outdoor in line-of-sight transmissions.
The only reliable modulation indoor turns out to be the COFDM links which are more expensive to achieve and is digital, so you have more frame delays caused by the digital encoding-decoding in DVB-T. The behavior of the COFDM modulation is that the frequency band used is narrow and constant, making it for a diversity receiver much easier to choose the best incoming signal.
You also have the WIFI transceivers, but they take easily a half second delay, which is not what I'm looking for either.
My previous reply is based on 3 things:
- 1. they mention AM?? modulation. Video transmission is not possible to get proper noise free transmission in AM, so it must be FM and an error on the webpage. Which makes me scratch my head if they are professional...
- 2. Since it is most likely FM modulation, I have enough bad experiences with this.
- 3. They have no Diversity receiving part, which will end up 200% in reflections.
Posted 23 August 2007 - 07:43 AM
Hi Brad, as far as I can see on the websites, they will use the analog FM transmission with the disadvantages I mentioned before.
The second unit will work better with the diversity, but still reliable error free video transmission is not garanteed.
It all depends what your needs are. If it's to verify what the camera operator is shooting, it will work fine with some distorted images now and then. If's to be used to record the video, it's not good enough.
Posted 28 August 2007 - 11:52 PM
This is my first post on this group. I'm a Video Assist operator in Montreal.
I've just receive a GX-68/M and a GX-68/HP with a M-806 receiver for trial from www.imagegearinc.com
At first look, it seems to work as good as a Modulus, but I need to do some "Onset" testing before give my final conclusion.
There's also a review of the SPX-68 from RF-Links here: RF-Links SPX-68S Transmitter Review
Posted 08 September 2007 - 12:47 AM
Haven't tried the Gx68...
I had an earlier models... now that said...
Ordering from rf-links is a bit of a one way street. If you don't like the product then be prepared to live with your mistake.
Want a demo unit? Well, no... not really...
Demo is stretching a bit, but how about a return policy? Nadda...
Why did I buy it knowing full well it could be a mistake?
At the time we were in a bit of a crunch and it was an affordable model. I too was attracted to the "video sender" wording, but beyond those words lies little truth. (well, it does send video... sorta).
In any event, Marc nailed about every problem without actually using the unit. My experience was not one of the best and it probably still sits in a box on my old desk.
At the time, that was what we had for the budget so while I knew it was a risk it was the only one the powers that be would take. For these types of purchases, research and don't skimp too much. It's better to waste on something useful then to simply waste.
Posted 09 September 2007 - 06:06 AM
You're right about ordering directly from RF-Links. I had serious issues with the guy there, voiced my opinion, and didn't order the product because of his ridiculous policies. But he referred me to Mike Wilder (firstname.lastname@example.org) at Image Gear (http://imagegearinc.com) who was very accomodating and allowed me the option to demo the unit and if I didn't like it, I could return for a full refund.
That being said, my initial tests were on par with the Modulus. I tested it side-by-side with two Modulus 3000's and had comparable results so I bought the RF-Links unit as it was brand new and less expensive.
I don't have a lot of on-set experience with it because I've either been on sets where they have their own transmitters or I use my Transvideo Titan (which I love). Did use it recently, however, and strangely it worked great the first part of the day, and then not so great the latter part of the day. No idea why. Thought heat, perhaps, but it never really got that hot. Since I had compared to the Modulus before I assumed it was just where we were working, but the video playback guy put up his Modulus and got a great picture which was good for the show but bummed me out.
Posted 09 September 2007 - 01:27 PM
As a follow up to my review of the SPX-68, I still stand behind the service of Mike Wilder at Image Gear and the side-by-side comparisons I made to the Modulus 3000.
Since that time I've had two on-set failures with the SPX-68S, at least one I believe to be heat related as Dan mentioned. The good news is Image Gear repaired / replaced them both out within 2-3 days at no charge (other than shipping) and that's not bad considering it had to cross the border.
The bad news is it weakened my confidence in the product, not to mention the immediate stress it caused during the shoots.
With that in-mind I just pony'd up last week for a Canatrans and have retired the SPX-68 to backup / rental status.
In retrospect it would have been nicer / better to have started out with a Canatrans or Modulus but as we all know the accessories investment as an owner/operator seems like a never ending journey... or maybe it really never ends at all? The SPX-68 at least got me started with a transmitter system, will be a good backup unit for the future and has more than paid for itself in rentals (I had Terry West make a dual 9 volt w/BNC adapter so it can be used with any camera or system).