frequency

[donkey]

I am seeing ALOT of transmitters using 433mhz 2.4ghz and 5.8 ghz. I also see alot of existing products using these same frequencies. is there a reason why these specific frequencies are used?
I have yet to hear of, for example, a 3.295ghz transmitter and reciever. Is this because it has been bought thus not allowing us to use it?
and hyperthetically if i did want to make a 3.295ghz transmitter/reciever package is there any way of making it as small as the existing products I find on the shelf without paying for a special RX/TX antenna set?

 

[(*steve*)]

Licence free spectrum? (or words to similar effect)

 

[GreenGiant]

it probably has a lot to do with antenna size, as well as making things common

433Mhz needs an antenna of almost exactly 1 foot (1.08) or almost exactly half a foot (6.48 inches)

2.4Ghz needs a 2.34 or 1.17 inch antenna

5.8Ghz needs a .97 or .48 inch antenna

3.295 would need a 1.7 or .85 inch antenna to work at its peak

also the higher you go in frequency the more clarity you can get, and the faster you can transfer data, 5.8Ghz phones will pick up less interference, where 2.4 might pick up a neighbors baby monitor, or crosstalk between phones

 

[Raven Luni]

But lower frequencies bend corners more easily

 

[donkey]

ok so far I understand that these frequencies are standard because they are open to public.

but hyperthetically I was wanting to have a 3ghz transmitter reciever, besides getting the rights to this frequency would I need a specialised chipset or could I somehow manipulate a 5.8ghz set to broadcast lower?
I have a project in mind but the dang interference is making life... lets say its slightly hard at the moment.

 

[davenn]

just to broaden your horizons a bit

these are referred to as the ISM bands they stretch from HF right through the microwave freq's.

"public" uses include 433MHz garage door openers, 2.4/5.8GHz video senders, cordless phones, LIPD's
(Low Intereference Potential Devices) to which any of my amateur friends and myself will tell you the last thing they are in low intereference. They are just a freakin' nightmare spewing garbage all over the chunks of spectrum they occupy.

We have all had a total guts full of them. Very few of them are running maximum legal power... most are well in excess of it.

cheers
Dave

 

[donkey]

the big issue i have is the project in mind needs to be "secure" I just need as little interference as possible and the only transmitter/reciever or transcievers I find use these frequencies.
I also heard from the local tele guy (optus here in australia) the new 4G rollout will be on the 433mhz band, if this is the case then that won't be an option at all.
as for the other 2 I could use them as this project is for outdoors and I can't think of too much that will be used over the distances i am trying at those frequencies(phones, router etc are 100m line of sight I am thinking 1km using trancievers to relay the signal)

 

[Mongrel Shark]

If you can get past all the interference in the 2.4 or 5.8 ghz ranges. You could just encrypt for security. Takes a good quad core a week or 2 to crack AES2. As long as you change the key more frequently than that it's do able.

Although it is a pain. If security is really a big concern your going to end up encrypting the transfer anyway...

Still doesn't help with interference though. But seeing as so many devices go way over legal max. You could just join the herd and use this and blow all the competition away. Shame it's so pricey though...
If you did want to go that way and needed more power you could add a 21dbi antenna from ebay....

Food for thought?

 

[davenn]

I also heard from the local tele guy (optus here in australia) the new 4G rollout will be on the 433mhz band, if this is the case then that won't be an option at all.

not a chance of that happening, it will be within existing cellular band freq's, there's not enough bandwidth at 433 MHz

Currently Telstra are using the 1800MHz cellular band for 4G, Optus are also trialling 4G on 1800MHz and Vodaphone and Optus have signed a network sharing agreement

cheers
Dave

 

[donkey]

mongrel, first of all hi am in briz.
second i saw those transmitter reciever packs but i think its over kill, and when I have an operational product working will show you all the idea as well as try an figure out the next few steps.

and davenn just my luck, yet another optus worker that gave me wrong info, I really need to switch carriers lol

 

[Mongrel Shark]

Lol. Hi from Palm Beach.

I'm about to dump optus for my internet for much the same reason. Customer service is just nonexistent. Except that means worse coverage and service with Vodafone, or going to Telsta (shudder). So I'll probably stick to being screwed by optus... Facepalm

I'd love to see your project or help out if I can. Finer details are probably over my head but I get the "Vibe" of most technology. Seem to have a knack for antennas despite my lack of finer understanding (ie I can bend a coat-hanger to receive any frequency you like, Also made some good ant's out of tie wire). Sometimes the answer is simpler than people think.

Good luck.

 

[(*steve*)]

We use Vivid wireless at our office (not in QLD) and it's actually pretty good. If you're after a "fixed" wireless solution I would investigate it.

I have a relative who gets poor signal with them and it's not real good, but after judicious placement of the base station he is much happier.

Personally I would go fixed line if at all possible (cable, ADSL, or fibre)

I have optus wireless service as a backup to my fixed line service (for work purposes) but unfortunately it doesn't work in the house.

 

[Mongrel Shark]

I'd love to go ADSL, But the lines in the area can't handle it ( well 2++ ) No carrier will promise me even 4mbps. I get up to 8 Mbps through my tethered phone, and 20+ Mbps through my usb dongle, with a 24 dbi ant I got on ebay for $12 lol. Only drawback is I keep cooking modems. The latest one lives in a plastic bag in a large jar of water to keep it cool..... Optus give me unlimited for $3 a day prepaid, I have been known to use over a TB a month and it's only $90..

I'll look into Vivid though. Thanks for the tip.

 

[donkey]

ok this is of the original topic, but seriously optus has just been no good to me. last year after 4 months of telling them i was losing data and them telling me speed was fine and me hitting my head trying to tell them the difference between data loss and speed we found out the local hub was handling too many connections, never heard if they fixed it.
I rang up once cos i lost the bill, 4 different people told me the bpay biller code was confidential and could not be given out over the phone.
in the past 2 weeks I have tried port forwarding for call of duty modern warfare 3, i rang them to help run me through it, the 2 problems i faced was i didn't know cisco setup and due to the 4 connected devices i couldn't tell which was mine. the first guy put me through to business department which was closed, the second chick told me my internet IP not the one for my computer and then told me if the one she provided wasn't right then i shouldn't have internet at all.
I rang another time they said they would get tier 2 tech to call me at 4pm, they made that call at 2pm the next day
then they have a thing called premium home services, which is actually another company all together and they charge $70 for a consult. after an hour on the phone to them they told me that the upnp part of the modem was faulty and I should get it replaced, but when i rang optus they wanted to send out technicians cos the frequencies they saw on their end showed the modem was working fine.
to top all of this of I have repeatedly said do not call me until friday or saturday as these are my only days of. guess how many calls I get monday to thursday?

but anyway back on track
I have an idea in mind but the issue is I highly doubt its possible. if for example i use a 433mhz transmitter could I somehow limit the power to make it transmit at 300mhz? or even do something to the antenna to limit it. I am just trying to get a bandwidth slightly of the commercial area and something I can play with.

 

[davenn]

but anyway back on track
I have an idea in mind but the issue is I highly doubt its possible. if for example i use a 433mhz transmitter could I somehow limit the power to make it transmit at 300mhz? or even do something to the antenna to limit it. I am just trying to get a bandwidth slightly of the commercial area and something I can play with.

Just be aware ... the ISM bands are there for a reason .... to be used for the sort of thing you want to play with. Playing on freq's other than those and you are inviting visits from the ACMA for intereference to other users on THEIR legit and paid for licenced freqs

Dave

 

[Mongrel Shark]

Just be aware ... the ISM bands are there for a reason .... to be used for the sort of thing you want to play with. Playing on freq's other than those and you are inviting visits from the ACMA for intereference to other users on THEIR legit and paid for licenced freqs

Yep. What he said! My Uncle got in big trouble as a young fella, when his quarter watt (when he cranked it right up) transmitter accidentally overrode a a fire brigades freq 300km away. (he was using that freq because it was so far away he didn't think he would be able to cause inheritance with such low power.) Problem was stratospheric interference and phantom zones can do weird and unpredictable things... He got his bedroom door kicked in (was an outside door) at 2am by radio inspectors. had to go to court. Was pretty serious trouble. Only reason he got away with it was because he knew so much about radio and was only 13...

Moral of this story. Don't mess around outside the legal freq's unless you know exactly what you are doing (if you don't have a ham lenience, don't even think about it). Even then you do so at considerable risk......


Re optus. Typical.... If someone wanted to provide reasonable telco service and have customer service, They would make a killing!

 

[donkey]

I knew there are limitations, and I am NOT doing anything right now, but my project will require little intererence to work properly.
size is an issue too as well as power consumption, the idea is nearly ready but I wanted to know in advance roughly how much room I would need if I were to go to another frequency? or even if it is possible? or if I can get a rx/tx set to a specific frequency and if so what size am I looking at?

the only thing I know for sure right now is that I want it to travel 100metres. I can't even tell you if I am streaming or not or what type of transmission (data or simple high low) yet as that is phase 2 of said project.

all I really need to know is size. oh and maybe a rough idea on power consumption so I can figure out rough idea on solar back up

hey mongrel re optus thingy... you got a few billion dollars? we could start our own lol

 

[Mongrel Shark]

How little interference do you need?

I remember my uncle (former Chief Head Executive Engineer in Charge, of one of the bigger regional commercial tv/radio networks in vic) saying the is no such thing as no interference.

Even if you get rid of all man made interference (RF magnetic flux etc etc, You got Buckley's on any freq). You will still have the earth, the universe, and mostly, the sun to deal with.

I'm thinking your going to have to reconsider the private, no interference part of your idea. If you are worried about eavesdroppers or meddlers, you can just encrypt. If your signal is so sensitive a bit of interference from say, some dude with an electric razor or a power drill, can cause serious problems. you need to change something, or be prepared for a lot of headaches.

Any HAM (or more experienced than HAM) people out there that can explain better?


re diy telco, If vodafone and optus keep going the way they are, we will be able to pick one up on the cheap soon.

 

[donkey]

its not eaves droppers or meddlers that concern me. what conerns me is the way I have it planned is a stream of data every, say, 30 seconds, until the device is "activated" then it switches to a constant stream at a different frequency or packet of data.
the fail safes will include low battery check and if the battery is dead then it will send no signal. this will put the whole system in jeapordy so I will have a special warning if a signal is not received every 30 seconds. there will only be a few times this will happen and except for interference the others are all bad.
to sum that up the system will broadcast until bad, if really bad system will not be able to broadcast at all, this will make sort of an emergency situation to get it rectified. if it ends up being something like a guy walked to close with his wifi enabled phone then people will start ignoring the emergency calls and render the system void

 

[Mongrel Shark]

Sounds like you need a "special" signal for a real emergency. If it get's no signal it should request maintenance rather than alert an emergency.


If it's really critical, then maybe think about 30sec pulse turning into "full power" constant signal. Or something different to the results of interference...... Or are there power supply constraints that would make that difficult?
Sounds like it's a monitor for some kind of critical system. So I can see why you want a freq that has minimal interference.
I'll leave it up to the people more experienced it radio in Aus to answer that. Best I can do is say look at the spacing between stations on a few frequency's (say CB, UHF, AM, Fm, TV etc) and see if a pattern emerges re station spacings. If you where really concerned it might be worth buying an "extra" station either side... (I have a few friends that are good with radio, so it's a bit of a week point with me, as I can ask for help easy.) Still going to get interference from Solar flares or who knows what. No matter what frequency your on..........