2.4 GHz FM ATV - a project concept
I've been searching about the internet, ATV magazines, etc... in search of building blocks for 2.4 ghz FM ATV equipment. I felt, with the recent explosion of consumer goodies in that part of the spectrum, that surely there would be a device already being mass produced as a wireless video sender that could serve as a platform for an Amateur Television system.
So far, the most viable device I've found is called "Wavecom Jr.", a consumer product operating as a short range video link on 2.4 ghz as a part 15 device. It is sold as a pair (1 receiver and 1 transmitter), operates within our 2.4GHz allocation, and uses FM for both video and audio. Initially, this sounds like just what the doctor ordered.
Here's product info on the "Wavecom Jr."
Here is the technical info I obtained from RF-Link's customer service folks:
The Transmitter operates with an output of about 1mW (0dbM) into an antenna impedance of 75 ohms. The transmitter is FM, and uses a synthesizer for frequency control. It's output frequencies are user selectable, and are: 2.411GHz, 2.434GHz, 2.453GHz, and 2.473GHz. The transmit Video bandwidth is 4.5 mhz.
The receiver frequency control is also synthesized. It's frequencies of operation are the same as the transmitter, and are user selectable. The receive sensitivity is spec'd at -90dbM for a clear picture (not sure what the s/n ratio would be, I forgot to ask that question). The range is spec'd at 300 feet with the built-in antenna, >2500 feet with an external antenna (no antenna specs there...).
According to RF-Link, the manufacturer's suggested retail price is $199.95 US. So far I've located them at Consumer Direct Warehouse, Radio Shack, and JDR Microdevices. The best price yet was from Radio Shack at about $95. Anyone out there located a better price than that??
The project is in it's infancy, and I'm open to any ideas/experiences that other amateurs may have on this topic. If you wish to share info, please drop me an email to email@example.com. I'll be glad to share anything I learn as a result of my experimentation. I'd also love to host any additional info on mods to the Wavecom here, so send me your info and pictures. Lots of people surf this site, so your info would help a lot of other folks!
Bulletin: 2.4GHz ATV Experimentation
The project concept being tested by the Arizona Amateurs on Television
Just off of the Tallahassee and HATS ATV mail reflectors: Feedback from Alan Glynn firstname.lastname@example.org about the work being done by a few members of Arizona Amateurs on Television. The following is a translation of Alan's email:
"I've seen quite a bit of interest in the 2 gig band in the last month or so on the net. I and several of my fellow club members (AATV, Arizona Amateurs on Television) have also been playing around with equipment for the band. The most promising, and simplest components we've found so far have been the WaveCom Jr transmitter/receiver combination."
"They put out about .25mw stock, out of the box. With the removal of the 9db internal pad, it ups the output to about 2mw. With a good feed and 18" dish...30db..we've now got 1W out on 2.4 gig..all this from off the shelf! Stock, in the clear, with the stock antennas, you'll get about 1/4 mile range. After the mod to 2mw, you'll get about 1/2 mile range. These are points of P-4 1/2 pixs."
"Now, please understand, these were informal tests, no attempt was made to define any parameters or any other esoteric features, just a couple of guys out trying out their new toys. Drop out rate is high at these extremes. A 3" movement takes you from P-0 to P-5."
"I have used a mimmic to raise the output to 60mw. It worked greatand all fit internally to the stock module!!! These units are extremely stable so the mods could be done by anyone the can run a soldering iron and see well enough to spot surface mount components. Oh yes, you do have to be familiar with a X-acto knife and be able to use one..?? We haven't had a chance to try out the new power level for distance..yet..but I'll let you know as soon as we do."
"DEMI makes an amp that puts out about 2.2w with about 10mw drive. See where we're going?? I'm pretty excited about a "new band" for TV. Lets see, I knew I was saving that old microwave oven for something...!"
"KB7OCB ,"Fast Eddie", as we affectionately call him, is our resident dish feed expert and has come up with some really innovative and high gain feeds for dishes and easy to build! Lets just say that 1Kw erp on 2.4g is just driver levels for him."
"The enthusiasum for 2.4g has overloaded our treasury and members pocketbooks thus we have a few units left over from our "bulk" purchase. If anyone is interested in these units on a first come first serve basis(via E-Mail to me) please let me know. We can sell them for $149 by cash/MO/certified check and we pay shipping. And yes . in answer to your next question, we are making a whole $8 on the deal...but its for the club. You can make the checks payable to me,the VP of the club, Alan Glynn..I'll make sure the money gets to the treasurer...HEH...HEH...?"
"All aside, if you guys are interested , its the simplest entry to 2.4g I know of. If you need any info let me know I'll feed you every thing I've got. I work out of town, so I can't always quarantee how soon I'll answer, but I will answer."
The "pad" is a pi network attenuator. It's located on the upper right-hand side of the module, when its held with the input pins facing up,and in the lower left-hand corner. There are three chip resistors marked 101,680,and 101. You'll need a magnifying glass of some sort to read them, unless you are a heck of a lot younger than I. Both 101's go to ground. The 680 is the one that bridges a gap in the trace. You must replace the 680 with either a 0 ohm resistor or cut a miniscule piece of copper (like the tape you buy to make traces on a blank board) and bridge the foil. If you attempt to us a piece of wire...you will get an impedence bump and lose substantial power. To actually remove the parts, I use solder wick to remove as much of the solder as I can, then use a dental pick/X-acto knife/or any pointy tool you own, to lift the device whie heating both sides of the chip with your soldering iron. They are tiny, you don't have to save the component if you don't wish to. They may or not break while removing. I personally do not save removed chips unless they come right off the board with minimal heating. The heating tends to debond the caps on the chip and you'll run into all kinds of problems later. Also one little trick for you techies out there, if you'll use silver solder on your chips, you'll get a better joint. You can also remove silver soldered chips with more success in saving them because silver solder tends to strenghthen the cap/chip bond, whereas regular solder tends to debond the cap on the chip. This info was in a circular put out by Sony for their tech service centers.
B - What is a mimmic and how do I get one or build one?
A mmic (I typo-ed in the posting) is a monolithic amplifier. A bipolar monolithic integrated curcuit. Aren't you glad you asked now???? In reality, they are tiny gain blocks, you only have to know that they are broad banded amplifiers. Several manufactures make them under various names, with Mini-Circuits probably the most visible to the ham community(they're on the internet, or you can call 718-934-4500 to order a catalog). They label theirs as Mar-1 thru 8 or another version is the ERA-1 thru 5. You can read the literature in the catalog on the individual characturistics. I chose the ERA-5 because of the gain and frequency response. They ae also very simple devices to install. They have 4 leads. Two are grounded, and the other two are input /output. The input is connected directly to the source thru a coupling cap(abt 10pf at this frequency) and the output goes to the next stage/antenna. You'll need to provide power to the output leg via a resistor and choke(see the catalog). A no-brainer!! They are marvelous devices and all the info need is in the catalog from Mini-Circuits. The other "cute" thing that mmic's are capable of, is paralleling for increased power... Read the catalog for more info.
C - Where do I get a DEMI amp ?
You can get the amps from Down East Microwave at http://www.DownEastmicrowave.com. The 2W version is probably much too heavy to launch in the average model plane. You'll probably have to be satisfied with 63mw. They have a catalog "on-line". The are probably the best source of microwave equipment we have. Excellent company!!!
D - Can I remove the existing ant. feed and install a 50 ohm feed to my ant?
Yes, but if you read my posting a couple of days ago, you see that it seems to be critical on coax length(at least with the coax supplied and my output tuning cap). Either use the original length(yes, just coil it up inside)or cut it in multiples of 1/2 wavelength, which for the stock coax is 1.88", and it should work okay for you. If you need something longer,i.e 10', you may need to install some sort of simple matching network. It will all depend on your soldering and coax cutting technique.
E - Do you know of any preamps on the market for the receiver ?
Yes, and I bought mine from DEMI. In kit form, with the power supply, I think they are around $45.00. The part number is 13NAHK (PHEMT wb5ula design with 17db gain and <.5dbnf) NICE amp!!!!
Here are some pictures, sketches, and plans for the 2.4 ghz tx mods:
Here's a shot of the Wavecom Jr. TX from the
component side of the PC board.
Here's a shot of the Wavecom Jr. TX from the
foil side of the PC board.
Here's a drawing of the Wavecom Jr. TX locating various adjustments and pinouts.
Here's a drawing of the Wavecom Jr. TX locating the point to pick up the 8vdc source.
Here's a drawing of the Wavecom Jr. TX locating the 8 db pad and outlining it modifications.
Here's a drawing of the Wavecom Jr. TX outlining the addition of the 60 mw mmic power amp stage.
Here's a drawing of...well, have a LOOK!.
2.4 ghz Info from Kip TurnerI just received this info from Kip Turner at email@example.com. Kip describes yet another possible power amp for the Wavecom Jr. tx that should make about 250mw. Here's Kip's message:
"I forgot to add that my unit came from Radio Shack. That should make these units locally available just about everywhere (at $149 sale price)"
Wow! Thanks for that good bit of info, Kip. If any others are working on this project and wish to share your info, please send me an email with any info you wish posted here. My address is: firstname.lastname@example.org
2.4 ghz Info from Tim O'BrienI just received this info from Tim O'Brien at email@example.com. Tim has some thoughts on another possible source for an inexpensive copy of the Wavecom Jr. Here's Tim's message:
Please let me know if I have been of any help, or if you can, confirm for me the info I am offering.
Thanks for that good bit of info, Tim. If any others are working on this project and wish to share your info, please send me an email with any info you wish posted here. My address is: firstname.lastname@example.org
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