Hello All,
What I can contribute to this discussion is:
- For FreeDV operation on HF I am using normally 100 - 200 W average
power. My PA is a 2,5 kW SSB type.
- I have now measured the average and peak powers using my WaveNode WN2
and KF-8KW RF Sensor, but just using my transceiver, so without the PA:
mode
avg (W)
peak (W)
PAPR (dB)
1600
1.5
20.8
11,4
2020
1.9
13.4
8,5
700C
1.7
12.9
8,8
700D
1.6
12.2
8,8
800XA
7.2
10.4
1,6
Maybe that helps.
73's
Gerhard OE3GBB
Am 18.06.2020 09:40, schrieb David Rowe:
Hi Take,
On HF channels OFDM is a neat solution to multipath problems like delay
spread and frequency selective fading. Single carrier modems are
possible but require a different design, in particular an equaliser to
handle the channel.
As Hams tend to have SSB radios, they are already designed for waveforms
(like analog SSB) that already have significant PAPR. So OFDM is
reasonable fit to available hardware, despite the PAPR issues.
Cheers,
David
On 18/6/20 10:20 am, Tsutsumi Takehiko wrote:
Hi Glen,
What is your position of Single-carrier FDMA or LP-OFDMA technology
compare to PARP reduction scheme which you have rich experience in your
memo?
I wonder why radio amateur society leaves PARP issue untouched when they
adopt OFDM technology.
Does it comes from SSB experience which has about 5dB PARP?
Regards,
take
de JA5AEA
Windows 10 版のメール <https://go.microsoft.com/fwlink/?LinkId=550986>か
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*差出人: *Glen English <mailto:[email protected]>
*送信日時: *Wednesday, June 17, 2020 8:09 AM
*宛先: *[email protected]
<mailto:[email protected]>
*件名: *Re: [Freetel-codec2] FreeDV Tx power
Hi David
I've been across OFDM PAPR reduction development for many years.
Most successful simple schemes involve some sort of selective mapping or
bit flipping.
-IE the PAPR is computed and an alternative trajectory is generated .
-These can be either tweaking the source bitstream slightly (many methods)
-and also providing overmapping of the constellation (say 64 QAM points
might only map to 48 unique symbols, giving the system a choice of some
other point that can convey the same data.
-and also deliberate FEC violation (modify the most encoded code and
remove/reduce the offenders)
-and also selective bit flipping - easy and fast.
I would encourage some form of PAPR reduction for any ham OFDM development.
Without it, OFDM is often and (and ignorantly) overdriven creating
spectrum headaches for adjacent channel users
-glen
On 17/06/2020 07:33, David Rowe wrote:
Hello List,
I've been working with Peter, VK3RV on the surprisingly tricky problem
of measuring FreeDV Tx power.
Over the weekend I built an inline "sampler" and tried a few averaging
options to measure the power of a 700D waveform on my spec-an. I am
using my IC7200 with the drive adjusted so that the ALC just moves. I
am sampling the power between the IC7200 and my ATU, which is connected
to a dipole on 40M.
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