I from Taiwan
How to improve those devices to make the reception more widely?
Max Range: 351 NM
https://zh-tw.flightaware.com/adsb/stats/user/peter79101622#stats-60905
Use equipment:
Raspberry Pi 3 + computer
FlightAware Pro Stick Plus FA-PROSTICKPLUS-1 ADS-B USB Receiver
Wire N TO SMA RG142
Antenna 12DBI
12dbi antenna? My DPD antenna is only 9 and it is one of the best you can buy.
Your range is limited by the curvature of the earth and your antenna height. There are exceptions with tropospheric ducting, but that is sporadic.
You may be able to improve reception by optimising the gain, using a better receiver (airspy etc), using a filter or an amp/filter.
Don’t think he was asking for advice.
Have you looked at his stats? 
Anyway the Airspy is always a nice but somewhat expensive option.
Edit2: He’s on a Flightfeeder.
Edit: Seems he is indeed asking
@peter79101622
What do you mean make the reception more widely?
You aren’t permitted to modify FlightFeeder systems.
They have very good reception anyway.
Don’t set the feeder-id from your Flightfeeder.
You want a new site for your Raspberry Pi.
(PiAware - Claim and Link a Brand New PiAware Ground Station - FlightAware)
If you have already set the feeder-id on the RPi, that can be corrected with the following commands:
sudo systemctl stop piaware
sudo piaware-config feeder-id ""
sudo rm /var/cache/piaware/feeder_id
sudo systemctl restart piaware
After that you should be able to claim a new site.
273 NM - Not too bad with an indoor $7 PCB Antenna and dump1090-mutability ver 1.14
Mlat feedback is NOT enabled (port 30104 has not been opened) as 1.14 is not mlat aware and mixes mlat feedback to data sent to sites. That is why you dont see any mlat planes on any map.
(This is a test setup for PI24 image from Flightradar24)
Indoor antenna can be received
not bad
I have applied to the official FlightFeeder
dump1090-fa
I want to ask
Is there a recommended ads-b antenna?
Filter or amplifier
It really depends on your location and your interest.
If you are in the country, you probably don’t need a filter.
If your interest is maximising your range, then a gain antenna and as much height as you can get (and probably an amp).
If your interest is local planes, a gain antenna and amp will probably just cause you problems.
how do you feed both antennas to the device at once?
The two antennas feed two devices (dvbt dongles). One antenna is connected to dongle for 1090 Mhz, and other antenna is connected to dongle for 978 Mhz.
Both these dongles are plugged into one RPi which has decoder software for both 1090 Mhz dongle (dump1090-fa) and 978 Mhz dongle (dump978-fa).
