I would add front end filter loss adds directly to noise figure which affects
sensitivity.
From: Chris Gustaf
Sent: Thursday, September 21, 2017 12:11 PM
To: af@afmug.com
Subject: Re: [AFMUG] radio specifications... HOW?
You are correct that wider front end filters give up masking and rejection of
out of band interferers, but the intermediate frequency (IF) and baseband
filters are what determines RX sensitivity.
In the case you outlined, if the channel width was say 56 MHz for both QAMs and
the tuning range was 200 MHz or 1000 MHz, there would be no real difference in
sensitivity for the same modulation/channel width. The 1000 MHz tuning unit
range may be more susceptible to interference outside 200 MHz filter range is
all- this depends on other radio design elements.
You can try asking the supplier for a Threshold to Interference (T/I) curve,
which will show how strong a like signal at various frequencies will cause BERs
on the radio. Most licensed radio manufacturers should have this data.
Chris
On Thu, Sep 21, 2017 at 10:22 AM, Josh Reynolds <j...@kyneticwifi.com> wrote:
It is my understanding that the larger the operational range of the radio, it
is using vastly different filters to accommodate that range. These filters give
up masking performance outside of the channel mask for an increase in range.
Those wider range filters end up costing the radio *selectivity*.
If this is incorrect, please say so.
On Sep 21, 2017 12:07 PM, "Chris Gustaf" <ch...@trangosys.com> wrote:
In general for each increase in modulation level it requires about 3 dB
more SNR (see below), and for each doubling of channel bandwidth you lose 3 dB
sensitivity.
SNR Requirements for Trango and others:
QAM/SNR (dB)
256QAM/26.1
512QAM/29
1024QAM/32.5
2048QAM/35.8
4096QAM/40
The frequency tuning range of the radio has nothing to do with the
sensitivity.
So 4096QAM requires about 14 dB More SNR than 256 QAM for the same channel
size, but since in this case it uses a smaller channel bandwidth it has a lower
noise floor by 7 dB as Forrest stated. The 4096 QAM radio will require a 7 dB
stronger signal to hold its modulation..
Hope this helps
Chris
On Thu, Sep 21, 2017 at 5:24 AM, Josh Reynolds <j...@kyneticwifi.com> wrote:
I would rather not name the vendors at this time.
On Sep 21, 2017 2:30 AM, "Mitch Koep" <af...@abwisp.com> wrote:
Josh
Will you shall the radio info?
Mitch
On 9/21/2017 12:57 AM, Josh Reynolds wrote:
The frequency agility between the radios is 800 mhz. Vastly
different radio filters.
Both are capable of similar channel bandwidths.
This is all done at MCS0 / QPSK
I'm comparing, basically, their sensitivity and selectivity. The
radio that is frequency capable of 200mhz is also capable of hitting 4096QAM,
while the radio capable of operating in a 1GHz range of frequencies is 256QAM
capable.
Basically, it's (the 256QAM radio) sensitivity at the same modulation
and the same power is wayyyyyy closer than I would expect it should be -
vastly different, and far cheaper components. TL;DR: I'm calling BS on the data
sheet :)
On Thu, Sep 21, 2017 at 12:23 AM, Forrest Christian (List Account)
<li...@packetflux.com> wrote:
Can you give specific examples? Having a hard time understanding
for sure the exact specs you're comparing.
In relation to the thermal noise floor: just reducing from 1000mz
to 200mhz will gain you ~7db of noise floor. But usually that's in a channel,
not in the entire 'frequency agility' area. Maybe they aren't all that
selective within the 1Ghz bandwidth.
I've never been able to find a chart of theoretical required s/n
ratio for each of the QAM's so I can't comment on how much difference there is
supposed to be - after all, with everything else being the same (channel,
modulation, power, etc), 256QAM should definitely require a lower signal
strength than a 4096QAM radio. They definitely shouldn't be the same with
the same channel width, unless one radio is noisier or more susceptible to
noise.
And sensitivity should just be about the receiver, not the
transmitter.
On Wed, Sep 20, 2017 at 9:20 PM, Josh Reynolds
<j...@kyneticwifi.com> wrote:
Can someone smarter than I fill me in on something? I'm comparing
some
radios here (no names...)
One radio is 256 QAM, with a 1000mhz operating range
Another one is 4096 QAM, with a 200mhz operating range
Can you explain to me how the sensitivity on the 256QAM radio, at
the
same modulation rate, same (scaled) power level, claims to be
with a
single dB or two as sensitive as the 4096QAM radio with an 800mhz
smaller operating range?
Anyone?
Thanks :)
---
Josh Reynolds
--
Forrest Christian CEO, PacketFlux Technologies, Inc.
Tel: 406-449-3345 | Address: 3577 Countryside Road, Helena,
MT 59602
forre...@imach.com | http://www.packetflux.com
