Tvheadend

Hi I have video pixelation.
I have hd-880d powered with an amplifier. I am 50km away from the emitter.
In tvheadend i have the following values in the status page in file attached
Do you have any thoughts or ideas
Regards,

Stéphane

TVheadend version :
HTS Tvheadend 4.3-1676~g91f6de4
Linux config
NAME="Linux Mint"
VERSION="18.3 (Sylvia)"
ID=linuxmint
ID_LIKE=ubuntu
PRETTY_NAME="Linux Mint 18.3"
VERSION_ID="18.3"
HOME_URL="http://www.linuxmint.com/"
SUPPORT_URL="http://forums.linuxmint.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/linuxmint/"
VERSION_CODENAME=sylvia
UBUNTU_CODENAME=xenial
dmesg :
dmesg | grep dvb
[ 89.627974] usb 2-1.4: dvb_usb_v2: found a 'Realtek RTL2832U reference design' in warm state
[ 89.687740] usb 2-1.4: dvb_usb_v2: will pass the complete MPEG2 transport stream to the software demuxer
[ 89.687750] dvbdev: DVB: registering new adapter (Realtek RTL2832U reference design)
[ 89.688238] dvbdev: dvb_create_media_entity: media entity 'dvb-demux' registered.
[ 89.697885] dvbdev: dvb_create_media_entity: media entity 'Realtek RTL2832 (DVB-T)' registered.
[ 89.721335] rc rc0: lirc_dev: driver dvb_usb_rtl28xxu registered at minor = 0, raw IR receiver, no transmitter
[ 89.721376] usb 2-1.4: dvb_usb_v2: schedule remote query interval to 200 msecs
[ 89.735454] usb 2-1.4: dvb_usb_v2: 'Realtek RTL2832U reference design' successfully initialized and connected
[ 89.735538] usbcore: registered new interface driver dvb_usb_rtl28xxu