I’m re-configuring the antennas on the house before the snow flies and I’m wondering how close (or far away?) I should keep my ADSB antenna from a newly installed HF end-fed wire antenna (100w max on HF 10-80 meters). Same question I suppose for the 2M/70cm VHF/UHF (50w max) antenna also poetentially nearby.
For years my simple monopole ADS-B antenna was located in my attic less than 0.5m from one leg of an 80-10 trap dipole. My recollection is that the ADS-B message rate greatly decreased while I transmitted on HF, but since my transmissions were intermittent, the aircraft count was largely unaffected. I don’t believe I ever tried adding an external filter before the SDR dongle, since the intermittent desensing didn’t seem to affect my FlightAware ranking.
If you use a resonant end-fed half-wave (EFHW), the antenna end is its voltage maximum/current minimum, so most of the radiation occurs away from the end. That will provide a greater effective distance between it and your ADS-B receiver. If you’re using a non-resonant end-fed antenna, e.g., those fed with a 9:1 balun, then that’s not the case.
Many filtered dongles include a preamp located before the filter, making the preamp potentially susceptible to overloading.
@keithma has his ads-b antenna and receiver mounted on his HF hexbeam. I don’t believe he has any issues with his transmissions affecting reception and his is one of the best performing stations here.
It will likely depend on what hardware you are using - some LNAs and receivers are more susceptible to being overloaded by out of band transmissions, whereas some are unaffected by it. The rtl-sdr.com filtered pre-amp is pretty good, but the uptronics one gets easily overloaded without good additional pre-filtering. The airspy is much more tolerant of strong signals than rtl-sdr dongles are.
Using an “orange” FA dongle with the FA antenna connected directly to the dongle. I’m going to have the ability to move it from the end to the beginning of the antenna wire if needed. Will have some options but in general, the box will be somewhere near the HF antenna.
My HF antennas are six meters higher than my ADS-B antenna and I have a decrease in traffic when transmitting especially using the linear. The higher the power output the larger the attenuation of incoming ADS-B signal. There is also a piece of my receiving Pi-chart that is directly in line with my HF balun where I dont see aircraft even when not transmitting on HF.
Working backwards, most RTL SDR’s have a pair of diodes protecting the front end. From this you can assume that anything up to 0.6V poses no threat.
An RF volt meter on the ADS-B feedline while you’re key down will quickly tell you if you have a problem that needs solving.
Hmm, just got notification of being tagged in this thread today, that’s three days late!
Basically what @caius said. You can see my ads-b aerial mounted on top of the hexbeam. I can run full legal squirt with the amplifier running on 40m, 20m, 17m, 15m, 12m, 10m and 6m and I have no problems using an Airspy with an RTL-SDR-LNA, signals don’t drop and the message rate doesn’t decrease. The Pi, receiver and the LNA are in a box at the top of the mast so everything is very close to the aerial.
What receiver/LNA combo are you using? The Uputronics LNA is absolutely awful when it comes to strong signals nearby. A couple of watts on VHF or UHF and it just shuts down (I’ve not tried HF near one).
As I said above, it’s all very dependant on what receiver and LNA you’re using. If you have the Uputronics LNA, just a few watts on 2m or 70cms will completely overload it the second you transmit.
Hex beams are HF hexagonal shaped antennas with driven element and a reflector for each band, most being for 20, 17, 15, 12, 10 and 6 meter ham bands. A extended version with a 40 and 30 meter band dipole added is also now available. You can build your own or buy a kit to assemble.
I would love to, but unfortunately I live in an apartment building, and the Building Management does not allow anything on outer wall or roof top. They are very strict in implementing this rule, but give exemption in one case only: Cell/Mobile Companie’s Antennas and equipment (because they pay them a very handsome rent… money money money).
Some buildings do allow installation of antennas on roof top, like this one: