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VHF Ethernet

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Rich Grise

Jan 1, 1970
0
Hi

I would like some help for creating wireless ethernet network using
VHF radio with frequency range of 130MHz-18MHz. The distance supported
shall be upto 100km LOS. Kindly advise on industry products available
for such option.

Is "130MHz-18MHz" a typo? Do you actually mean "130MHz-180MHz"?

Or are you just another googler that we'll never hear from again? The
answers don't just show up on your desk - you have to come back to the NG
to read them.

Good Luck!
Rich
 
R

Robert Baer

Jan 1, 1970
0
Jan said:
Sometimes it did not finish at all.... :)

It is not simply 1200 bits / second, but the packets are send as a frame,
sync pattern first, CRC is added, then the transmitter waits for a reply
(ack or reject if received CRC was wrong, because of for example interference),
and then and only then (if the band is free from other transmitters, some wait
time the transmitter listens) the next packet is send again.
Hours.
Thanks; i will stay with dial-up...
 
O

ok

Jan 1, 1970
0
Is "130MHz-18MHz" a typo? Do you actually mean "130MHz-180MHz"?

Or are you just another googler that we'll never hear from again? The
answers don't just show up on your desk - you have to come back to the NG
to read them.

Good Luck!
Rich

yes its 130MHz-180MHz
 
E

Eeyore

Jan 1, 1970
0
ok said:
yes its 130MHz-180MHz

Have those who licensed this band considered the impact on air traffic
communications?

Graham
 
R

Rich Grise

Jan 1, 1970
0
yes its 130MHz-180MHz

I'm sorry for the "Googler" crack - I've seen that you're not some
hit-and-run dweeb, but a serious questioner.

Unfortunately, I don't actually have an answer for you. )-;

Regards,
Rich
 
J

John Barrett

Jan 1, 1970
0
ok said:
yes its 130MHz-180MHz

we still need to know how wide a slot you have in that range ?? 5khz ?? 10
?? 50 ??

cant do anything more than we have without knowing how much space we have to
work in !!
 
J

joseph2k

Jan 1, 1970
0
ok said:
We have a licence for a particular frquency in range specified. No
chance of geting arrested we are doing it all by legal means. Thanks
to people all for the answers. Looking for right solution. thanks

You had better read your terms of licence a LOT better. It does NOT support
that bandwidth in that frequency range.
 
J

John Barrett

Jan 1, 1970
0
joseph2k said:
You had better read your terms of licence a LOT better. It does NOT
support
that bandwidth in that frequency range.

OHHH get real -- you can run TCP/IP over packet at 1200 baud FSK in 5khz FM
bandwidth, and if you didnt mind moving at a crawl -- you could kick down to
110 baud and do it in less than 1khz of bandwidth.. if we can get away from
radios with voice front ends, we can get up to 9600 baud out of a 10khz QPSK
channel, but there doesnt seem to be much off the shelf hardware for that
one -- will have to piece together a system for that.. anything over 9600
will take a fully custom solution and a wider channel to run it on.

Thats why I keep asking how much of a slot he has so I can pick a modulation
scheme that will best use the bandwidth he does have allocated !!

OK keeps asking for commecial solutions -- and I can get him 1200 baud off
the shelf -- but he isnt going to do any better than that with OTS hardware
in that frequency range without a custom solution -- and if he has more than
5-12 khz of bandwidth available, it WILL take a custom solution to get the
best use out of it.

other than that -- getting VHF to go 100km just takes a coupla of yagi beams
and some reasonably high towers to get a clear line of sight

the only other thing thats really going to hurt him is if he really only has
bandwidth for one channel -- if so -- he is stuck with half duplex and its
going to be dog slow no matter what the baud rate is... he would be a LOT
better off if he had 2 channels spaced 3-5mhz apart to run full duplex
 
J

joseph2k

Jan 1, 1970
0
John said:
OHHH get real -- you can run TCP/IP over packet at 1200 baud FSK in 5khz
FM bandwidth, and if you didnt mind moving at a crawl -- you could kick
down to 110 baud and do it in less than 1khz of bandwidth.. if we can get
away from radios with voice front ends, we can get up to 9600 baud out of
a 10khz QPSK channel, but there doesnt seem to be much off the shelf
hardware for that one -- will have to piece together a system for that..
anything over 9600 will take a fully custom solution and a wider channel
to run it on.

Thats why I keep asking how much of a slot he has so I can pick a
modulation scheme that will best use the bandwidth he does have allocated
!!

OK keeps asking for commecial solutions -- and I can get him 1200 baud off
the shelf -- but he isnt going to do any better than that with OTS
hardware in that frequency range without a custom solution -- and if he
has more than 5-12 khz of bandwidth available, it WILL take a custom
solution to get the best use out of it.

other than that -- getting VHF to go 100km just takes a coupla of yagi
beams and some reasonably high towers to get a clear line of sight

the only other thing thats really going to hurt him is if he really only
has bandwidth for one channel -- if so -- he is stuck with half duplex and
its going to be dog slow no matter what the baud rate is... he would be a
LOT better off if he had 2 channels spaced 3-5mhz apart to run full duplex

Just a little up from your reply to me is OP's 18MHz bandwidth requirement.
That is rather more than 9600 baud. That is why no licence covers it.
 
J

joseph2k

Jan 1, 1970
0
John said:
we still need to know how wide a slot you have in that range ?? 5khz ?? 10
?? 50 ??

cant do anything more than we have without knowing how much space we have
to work in !!

OP wants an Ethernet like link, 10 MBits/s and up. Just won't happen on
that band, not even esperimentally. WARC and the national and regional
watchdogs won't permit it. That is why i told OP to reread his license.
 
J

John Barrett

Jan 1, 1970
0
joseph2k said:
Just a little up from your reply to me is OP's 18MHz bandwidth
requirement.
That is rather more than 9600 baud. That is why no licence covers it.

Its a communications problem -- in one post he sez 130-18 is a typo and it
means a frequency in the range of 130-180 -- never does he come flat out and
say "my allocated bandwidth is"

FSK (1200) and QPSK (9600) modems for VHF are available OTS and run in a
"standard voice bandwidth channel"

there are better modulations to use, but all of them pretty much require DSP
to pull off -- FHSS, et al, but they can be designed to include forward
error correction to mitigate initerference induced errors -- a feature that
neither FSK or QPSK has in off the shelf implementations -- and which is
probably going to be needed for the specified range -- half duplex is going
to be bad enough without retransmitting any more than absolutely neccessary.
And I seriously doubt hs has 2 split frequencies for a full duplex link.
 
J

John Barrett

Jan 1, 1970
0
joseph2k said:
OP wants an Ethernet like link, 10 MBits/s and up. Just won't happen on
that band, not even esperimentally. WARC and the national and regional
watchdogs won't permit it. That is why i told OP to reread his license.

an "ethernet-link" link means it carries TCP/IP data -- available bandwidth
and modulation style determines the maximum possible speed :)

and I agree -- he needs to read his license and tell us what his allocation
is !!

Though he really already has his answer for "commercial implementations" --
1200 or 9600 baud half duplex -- thats all he'll get off the shelf in that
frequency range no matter what bandwidth he has been granted.
 
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