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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 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
webmaster@teara.org. 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 wg7l@worldnet.att.net 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."
Here are some questions recently
fielded by Alan about the 2.4 ghz project:
A - How do you remove the pad ?
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:
I just received this info from
Kip Turner at kip@mindspring.com. Kip describes yet another possible power amp for the Wavecom Jr. tx that should make about 250mw. Here's Kip's message:
"Hi,
I'm playing with a Wavecom Jr for possible repeater linking, etc. The
pad is removed and I get several mW out. I have the Motorola MRFIC2403 GaAS power amp (not installed yet). This runs on +5 V DC + neg bias (depletion mode FET's) and should give 250 mW out. It's vailable from Newark @ <$10 each for quantities of one (+S&H,taxes, min.order and all that good stuff). It looks like the easiest way to boost the power at low cost. You might want to check it out! The chip is an SO-16 dip (very tiny...for those who can't see) and has a nominal 23 dB gain, peaked at 2.4 GHz."
In a second Email from Kip, he writes:
"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)"
Kip ( W4KIP )
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:
webmaster@teara.org
2.4 ghz Info from Tim O'Brien
I just received this info from
Tim O'Brien at tim4othy@socal.rr.com. Tim has some thoughts on another possible source for an inexpensive copy of the Wavecom Jr. Here's Tim's message:
"Hi,
You probably already know more about this than I do, but here it is. As far
as I can glean from what I have read, the Wavecom is exactly the same unit
as a number of other brands sold under other names, such as the Emerson
EVS5000. I believe that they are all made in China. I have bought some of
these at Supercircuits.com for $79.95 for the transmitter/receiver set.
Extra receivers are only $35 or $40.00, much less than what I have seen for
others. Extra transmitters are about the same. In their catalog the set is
referred to as the MVL-1. I am a complete novice when it comes to this
stuff, but when I cracked open my Emerson and compared it to the photo of
the Wavecom circuit board at your site, I could see no difference. The three
key resistors do have different numbers than the numbers mentioned by Alan
Glynn, however.
Please let me know if I have been of any help, or if you can, confirm for
me the info I am offering.
Sincerely,
Tim O'Brien
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:
webmaster@teara.org
Alan Glynn wg7l@worldnet.att.net
Here are some questions recently
fielded by Alan about the 2.4 ghz project:
