While I certainly appreciate your excitement over EDM, you are quoting people that represent the company. Not exactly an unbiased opinion. The first quote talks about looking at a spec sheet. What spec sheet? The Chinese units do not ship with one. They do not quote actual independant test results let alone their own test results. The second quote is equally as muddy. In the second quote, there is speculation that if given the right circumstances something bad could happen. Again, no evidence, just theory. I would be curious if that pirate radio station is not in some way affiliated. I am very skeptical like that.
In any event, I look forward to your report on your unit when it arrives. taybrynn wrote: Here are a couple comments from the yahoo EDM group, when I asked them to comment on the chinese recievers mentioned earlier in this thread. Several other users also replied, all basically saying these transmitters are junk for one reason or another -- most already mentioned here. They may work perfectly well, as Jeff mentioned, but what they are also doing (with unintended harmonics and spurs) is the biggest problem and risk.
They have high signal to noise ratios. Looking at the spec sheet of one of these Chinese transmitters, quote the signal to noise ratio (SNR) around 40dB. That is awful! Our LED series makes 60dB or better and the LCD series typically makes more than 75dB and some even up to 85dB.This is the type of figures you would find in a professional commercial exciter. If you take one of these low quality transmitters, kill the audio input and transmit a dead carrier while listening on a good quality FM receiver, with the volume turned up, and close your eyes, you will imagine that you are at the beach with all the "Shss" background noise you will hear. This is a result of the poor VCO designs used with high levels of phase noise on the carrier. There are also reported problems with the 2nd harmonic from these transmitters almost equal in level to the first harmonic which is the intended frequency. This second harmonic will fall in the low VHF TV bands (174MHz and up) and cause massive interference. This will lead to complaints and the get you into serious trouble if the authorities investigate this. Spurs may also leak into the aircraft band above 108MHz and you will also have the aviation authorities down your throat.
Another example from the EDM engineering team:
Our engineering department gave this example of how spurs can end up
in the aviation band.
Examples:
These transmitters typically use a clock frequency of 7.6MHz for the
frequency synthesizer. Because this clock will also have harmonics at
(15.2MHz, 22.8MHz, ...). If special precautions are not taken to keep
this components from coupling into the VCO as a unwanted modulation
spur, some image of your transmit signal will appear at these offsets
on either side of your transmit frequency.
First case: You transmit on 100.4MHz with a high level spur 7.6MHz
away. You will then have a signal interfering on 108MHz in the
aircraft band. If this spur is of significant amplitude and your near
an airport it will be investigated.
Second case: You transmit on 106.3MHz. The 2nd harmonic of this clock
appears at 106.3MHz + 15.2MHz. This will cause a signal at 121.5MHz.
This is the international aircraft band emergency frequency! You can
think what the consequences of this would be! These transmitters with
powers as high as 15W are like an accident waiting to happen.
EDM Team
Last edited on Wed Feb 20th, 2008 09:25 pm by iresq
Your right, I probably shouldn't be so trusting after asking a company about their own products -- duh!
But, getting a bunch of emails and eventually a call from a record producer who has also been doing radio for over 30 years ... that was a real confidence builder (in EDM). These guys raved and had no reason to do so financially speaking.
This guy, and Steve over at Radiobrandy don't seem to benefit in any way ... but they were extremely positive about these units ... so I just had to give them a try.
I'll hold off my blabber mouthing as much as possible, till I gets some 'hands on' experience with these units.
So EDM seems the way to go. Now where is their web site? I tried EDM, EDM transmitters and a few other combinations through google and got everthing but what I was looking for.
It would be premature to say that ... but its looking very "encouraging" from my research thus far.
Here are the links for EDM --
http://www.edmdesign.com/ -- note: the links below are embedded in the LCD graphic at the top of the screen, kind of confusing till you get used to it.
I have only one last thing to say. I hate my Ramsey. It was nothing but a waste of money. I get catalogs from them regularly, and throw them in the trash. I won't buy another thing from them in his life or any other.
I absolutely love (regardless of the opinions of others) my experience with the 1 watt transmitter and the .2 watt transmitter I bought for H/K. Both work very well. I tuned my aircraft reciever to the mentioned frequencies, while retransmitting my Sirius radio on the mentioned frequencies and there was zero indication that there was a signal be transmitted on these frequencies. When I searched the entire aircraft band, there were no signals being created by my H/K. So, while I have heard of this happening with some radio transmitters, it's not happening with these two transmitters.
Jeff
____________________ Get yourself a ServoDog. You'll be glad you did!
Jeff, thanks for posting your experiences and opinions.
Untill recently, I had only heard good things about the Ramsey transmitters. In the last couple weeks, my impression has changed for the worse ... as your not the only one who has had problems with them.
And you also definately not alone in being perfectly happy with the ebay transmitter that is very affordable.
Maybe its is just like how people used to tell me that my gigantic montgomery ward speakers were crap ... but to me, they sounded awesome ... and thats what mattered.
taybrynn wrote: Maybe its is just like how people used to tell me that my gigantic montgomery ward speakers were crap ... but to me, they sounded awesome ... and thats what mattered.
Funny you say that. I had a set of Klipsh horns when I was overseas. They made the best sound I ever heard, and all I got from others was "why'd you buy that junk" I have semi bad hearing and they fit me just right. I wish I still had those things. But i I did I'd really be deaf by now.
Jeff
PS I don't know where I read about electronic devices causing a carrier on the emergency air frequencies... but you are very right when you sat they investigate it. The story I was reading had to do with an illegal unit used to crack Sat TV encoding up in the G/W north. The person got busted since the thing was continuously triggering some alert system at a nearby airport. I wish I could find the article again...
____________________ Get yourself a ServoDog. You'll be glad you did!
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