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tkilloren

Antenna for Part 15

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I am trying to get the most distance while staying Part 15 compliant.

My application for surface use, so "line of sight" is really not in play here.

I bought a commercially available high gain (8db as advertised, about 8.5" square) antenna for my receiver, hoping that this would boost my range. Remember that Part 15 Tx is putting out well under 10mW. This patch antenna actually resulted in less range than the PCB (on board patch) antenna.

I have been reading the various threads on this forum to try to get smarter. Someone (Terry, I think) mentioned that the larger patch antennas won't improve your range if the Tx is under 200mW.

Since I make my livelihood making patterned, RF substrates (amplifiers,attenuators, antennas, striplines, etc) on alumina (dielectric constant of 9.9) for both commercial and military ciustomers, I am wondering if I could make my own patch antenna on alumina for my project.

I know squat about RF design, but I do know that the dielectric constant of alumina has everything to do with the way these RF devices perform.

The project patch antennas discussed on this site use air as the dielctric (dc=1).

Question:

How does the dielectric constant of the "insulator" between the antenna element and the ground plane affect antenna performance?

Can I use this technology to build a patch antenna on alumina to replace the PCB patch on my Rx?

You guys are good!

Tom

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How does the dielectric constant of the "insulator" between the antenna element and the ground plane affect antenna performance?

It affects the size of the antenna and the losses between the drive element and the reflector. You want these to be as optimized as possible. You get this with the idealized air or vacuum dielectrics. All other practical dielectrics will reduce the patch's element dimensions and hence reduce the theoretical gains.

My advice: Build the GP Patch for the Rx. Do NOT use any coax for the feedline!

Use a ground plane antenna on the Tx.

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Yes, I've got the message loud and clear, from the many posts, that coax is verbotten.

I currently have about 8" of coax between the Rx and the patch antenna. I will get rid of it and report back.

I will do some more research on the alumina as a dielctric. My military customers always specify the highest purity alumina (99.6%) available, with the best possible surface fininish for their devices (usually around 40Ghz). Metal thicknesses (gold) is also critical to performance......typically 3um (micrometers). Substrate thickness is also critical (+-.0005")

Thanks,

Tom

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If you mean me ? I dont remember saying that as most of the time I only use 10mW myself. I tried to copy a quad patch design a while ago but it was no better than a single patch. The pcb I used looked identical but it must have been different some how. If you are going to use low power like me I recomend you stick to simple aerial designs and even then some basic test gear is a great help. Good luck with it anyway, its nice to see sombody else going the low power route instead of just throwing more power at it. Let us know how you get on !

Terry

UK

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Yes, Terry, a power meter to measure signal strength would be a huge help. I will poke around on ebay and see if I can find something. When you're working from a knowledge base of zero, as I am, it is certainly tempting to just add more power, indeed. I am beginning to think that my vision of building a reliable surface system with a range of 1000' may not be possible within the Part 15 constraints......but I'm gonna keep pluggin' away at it....for a bit longer, anyway.

I'll keep you posted if I should stumble on anything interesting.

As always, thanks for all the comments,

Tom

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Hi Tom, how much power is your transmitter ? I get 1/4 mile very good and up to 1/2 mile with dropouts on 10mW.

Terry

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I have not been able to find anything about the transmitted power of this unit. Maybe someone is familiar with this particular model as they are quite popular.

http://www.protectiondepot.com/cv991.asp

I'm getting about 400' right out of the box. I bought (from Supercircuits.com) the MVR-8 High Gain Rceiver with 12dB circular patch antenna, which as I said earlier did not improve performance at all.

This receiver looks virtually identical to the one that came with the CV991 system, with the exception of a few different components on the pcb....it is advertised as a "hot" receiver.

The antenna came with 3' of RG58U coax with a large N connector at the back of the patch, and a small N connector on the other end. The small N connector was attached to the pcb with two 8" wires (fairly heavy guage). I eliminated the small connector by soldering the coax (shortened to 8") directly to the pcb. Again, no improved performance.

I tried replacing the on board Tx antenna (patch) with a 4" dipole (?)......a rubby ducky style antenna that came with another 2.4 Tx that I have. No improvement.

I suspect the Tx is well under 10mW....maybe as low as 1mW.

I have a friend who is a HAM. I'll see if he can help me read the Tx power. That may be a good place to start.

Tom

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Im starting to loose the thread here Tom !

The small N connector was attached to the pcb with two 8" wires (fairly heavy guage).

This bit confused me the most, maybe its just me but is there any chance you can post some pics of you mods so I can get a better idea of what you have done ?

I do think you will have a hard job if you are using under 10mW though :(

Terry

UK

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The CV-991 is a FCC Part 15 registered consumer device. Its measured radiated RF is ~23,700uV/m-AT-3m. The FCC limit is 50,000uV/m-AT-3m. Effectively, this is less than 1mW driven into 50 ohms. With the 12dB Rx antenna, the effective power is probably 10mW.

With registered microwave based video equipment, a mobile ground based application's range will be very limited. Especially if it is used near structures. FWIW, microwave RF based ground applications are tough even for higher power unless it is fixed line of site and nearby structures are minimal.

I'm not sure what your performance requirements are, or the operating conditions. But, if it involves long reliable range then it will be a tough nut to crack with registered (license free) equipment. It may even be tough with higher powered gear (depends on the environment).

The N connectors are not very lossy. Removing them will not impact performance if they are built to typical N-connector standards. A patch antenna on the Tx will add to the mobile challenge. You should consider using a dipole or ground plane design on it. I understand they did not seem to help, but if correctly designed and installed, they will help a mobile installation (versus a directional patch on the Tx).

Attached is a schematic of the CV-991 Tx.

cv991.pdf

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Thanks. As always your input is invaluable.

Unfortunately, with the consumer oriented products, very few of the resellers offer the power ratings of these devices, so it is very difficult to shop for the highest performance

systems. They all say "long range".

Two questions:

Will using an amplifier on the Rx void the FCC compliance?

I checked out the Down East Microwave site that you mentioned. They seem to have a vast selection of amplifiers, with several that look like good candidates for this 2.4 system. Any thoughts or recommendations?

And finally, these guys (see link) admit to having not done any serious lab testing of this ground plane antenna, but they are claiming (and they have no reason to exaggerate as they are not retailers) to get 400 to 500 meters range (LOS) on a surface mobile application.

The design is very small which meets my needs. It's something I could put together in an hour, so I bought the parts at Radio Shack and will slap one together tomorrow.

Anybody familiar with this little "spider"?

http://flakey.info/antenna/omni/quarter/

Omnidirectional is really where I would like to end up. These patch antennas are VERY directional. Can I put one of these (spider ground plane) on each end (Tx and Rx)?

Tom

P.S. Terry, I'll see if I can snap a few pictures and post them on a hosting site.

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...very few of the resellers offer the power ratings of these devices, so it is very difficult to shop for the highest performance

Equally important is the Rx's performance -- its all over the map when it comes to these consumer devices. As far as Tx power goes, you can safely assume that all the PArt 15 approved wireless video Tx's are a bit less than .5mW of effective radiated power.

Will using an amplifier on the Rx void the FCC compliance?

When it comes to Part 15 registered RF products, the FCC is primarily concerned with the transmitter. The Rx's seem to be open territory (even though they are usually FCC certified). But, if you are planning on turning this into a commercialized product then you should budget for the recertification of the Rx/preamp.

I checked out the Down East Microwave site that you mentioned. They seem to have a vast selection of amplifiers, with several that look like good candidates for this 2.4 system. Any thoughts or recommendations?

They offer a kit for a VERY low noise RF amp (<.5dB at 2.4Ghz). I think it is about $50 or so. Higher noise floors will be counterproductive. As far as gain goes, every 6dB will double your range. But I doubt that the dynamic range of the consumer Rx's will tolerate huge amounts of additional gain. I would hope that 6-10dB would work OK (might be a bit overloaded at short distance).

...but they are claiming (and they have no reason to exaggerate as they are not retailers) to get 400 to 500 meters range (LOS) on a surface mobile application.

Yes, but that is in a lower bandwidth data app that is probably using spread spectrum (where the effective power can be as much as 1 watt). Apples and oranges, as they say.

BTW, this is a much more efficient (assembly wise) ground plane design from yb2normal: http://www.yb2normal.com/antenna3.html

Omnidirectional is really where I would like to end up. These patch antennas are VERY directional. Can I put one of these (spider ground plane) on each end (Tx and Rx)?

As mentioned before, I suggest a Patch on the Rx and a Ground Plane antenna on the Tx. Omni on both ends will doom your mobile microwave application unless you are going to operate this in an area free of structures (no buildings, cars, etc. for hundreds of meters). Two things to note: (1) You will need some directivity to reduce multipath interference (2) Omni's are much lower gain designs. A 6-8dBi patch attenna on the other hand will give you a practical beamwidth.

I'm not sure what you are building. But if it is for personal hobby use, why not just obtain a ham license and go for a little bit more RF power. A 50mW Tx would really help out your efforts. There are other things to consider too, all of which depends on your required performance and operating environment.

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I agree 100% with Mr RC-CAM, you could also have a look here for a bit of info on pre-amps http://www.rc-cam.com/forum/index.php?show...ic=324&hl=Terry .

It will be good to test all your equipment using low power but I am sure at the end of the day you will need a bit more. Much better than just blasting out power you only need because your set up is so poor though.

Terry

UK

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Thanks guys. The news is not encouraging for my Part 15 application.

As I said I will post some photos on a hosting site. If nothing else, I think you'll get a kick out of my rig. My P/T aluminum components are currently out for black anodizing, so it will be a week or so before I get it all back together again.

BTW, remember the noise issue with the BEC? Well I received and installed the Kool BEC and there was no improvement. Mr. RC-CAM suggested that the noise could be coming from a variety of sources, including the battery pack. Well, guess what? I swapped out the battery pack with a different type (same power of course). NO MORE NOISE!

I know I keep saying it, but you guys are GOOD!

Anyway, I now have a spare BEC. Not to worry, I'll use it.

I built up that little "spider" ground plane antenna today. Looks neat! I'll try it out in the next day or two.

I know, I'm using the "shotgun" approach of problem solving on this project, but when your knowledge base(in radio) is zero, that's what you do. I'll tell you one thing for sure.....I'm havin' a helluva lot of fun, and learning as I go. Can't beat that.

Tom

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Well, all is not lost after all. That little quarter wave ground plane "spider" antenna was just what the doctor ordered. The impovement in picture quality was immediate....as soon as I powered up (in the house) the difference in video image quality was very noticable.

I haven't completed line of sight range testing, but I can say that I was getting a decent

(unstable but useable) image across 600' through dense woods, buildings, fences, and up and down terrain.

This was using the 12dB patch on the Rx and the quarter wave GP on the Tx.

I was able to get 600 feet LOS (that's as far away as I could get in this location) with a "lock on" image and a beam width of right around 100 degrees.......all Part 15 legal.

I wouldn't be at all surprised if this combo does 1500' or more in open country, based on what I've seen today.

Happy camper :D

Tom

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That is good range.

Keep in mind that your equipment is no longer FCC Part 15 compliant. The Tx antenna upgrade voided the device's certification. Another good reason to earn the technician class ham ticket. ;)

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Yeah, I meant to add "I think" after that ".....and all Part 15 legal" bit.

Details, details.....we'll worry about that later. For now, we'll be content to look at the pretty pictures on the monitor....they been a long time comin'.

Tom

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