Antenna & Coax Questions

Hi all,

I have just set up a feeder with the ADSBx starter kit (the blue SDR) and it works pretty good but due to my location (LOS due to terrain) I need to put the antenna in the attic (roof antenna isn't allowed in my condo community). Going off wiedehopf's hardware list, I have a few questions:

1. If I'm understanding the specs for the ADSBx blue SDR and the information in a thread in another part of this forum, I don't need an amplifier at the antenna end if I get the Proxicast 50' LMR400 cable becasue the SDR has an amplifier and 1090MHz filter built in. Have I understood correctly?

2. As noted above, terrain makes for some range issues in some directions. I'm leaning towards the ADSBx 1090/978 combo antenna because it's easy for me to get, but I'm wondering if a larger antenna like the 1.2m long Pimoroni or 57" DPD outdoor antenna will get me even better range?

3. Is it correct to assume that since the antenna is inside the house in the attic, I don't need to worry about extra grounding (lightning protection, etc.) as you do for an outdoor antenna? Just connect the coax and go?

Thanks in advance for the help.

 

Welcome to feeding!
to your questions:
1. An additional LNA near the antenna is used to overcome coax losses, not increase range. 50' of LMR-400 is about 4.5 db loss at 1090 MHz. Not the end of the world but more that 3 db should be avoided if possible. Can you shorten the cable in your install condition?
2. The standard ADSBx combo antenna (5 dBi gain) will overcome the coax loss, so since you are installing in an attic, I would not fuss with a higher gain antenna. Since you are terrain constrained, you might actually be better of putting the antenna, assuming you have a window that faces the area of interest than in the attic. Consider your roof material too. If you have a metal roof, or a massive roof like concrete stay out of the attic. Standard wood frame roof is OK, but be aware that even plywood based roofs have aluminum foil layers for heat rejection as required for current energy efficiency codes, so that's not good. If you have any metal in the roof system at all, forget the attic.
3. Yup, if your attic has no metal, just connect and go. I would however recommend adding a static ground near the antenna to some electrical ground. Won't stop lighting, but will reduce the possibility of static discharge roasting the SDR or Pi.

 

He said he can't go on the roof because of HOA restrictions. Attic or window antenna mount are the options. Sorry, I was wrong about 50' cable attenuation. It's under 3 db.

 

If JPM is in the USA, and his house was built after 1992, his roof has aluminum foil laminated to the plywood, so attic mounting is a non-starter for any serious antenna for any band. Not sure what your building codes are where you are. Germany?

 

Thanks for the responses. Looks like I'm on the right path.

I'm in Canada, and we don't have the foil laminated plywood on our roofs as far as I'm aware. I know mine doesn't. I've been moving the receiver around the house to find the best location and so far the attic gives the best coverage. Height is trumping the line of sight through the window I guess. One more window to try this weekend and then I will know for sure.

The little antenna with the kit is doing surprisingly well given the obstacles (inside, LOS due to terrain, etc.). The external one is mainly because I have no power in the attic and I think the temperature variation is too great for the Pi or SDR (ambient in the winter, so down to -20 or -30C, and hot in the summer, probably 50C or so), so I want to keep them in the house. And of course any additional range from a bigger/better antenna will be welcomed.

(As far as I remember, roofs around here are plywood, a layer of some sort of sheet (Tyvek?), a layer of rubberized sheet over the few feet near the eaves (to prevent damage from ice dams), and finally asphalt shingles.)

 

Hey JPM, how is your project going? What is your feeder ID? I'd like to look in.
My current feeder while I build a remote to put on a hill behind me, is an outdoor antenna (the one ADSB-X sells) on 15' of LMR-400. I have an end gable that is protected, so I drilled through the siding with a rain tight bushing, and then through the ceiling of a nearby closet as I had no power in the attic, like you, don't want to climb in there, and I'm in Hawaii, so the attic can get hot. I just used Velcro to attach the Pi case to the wall near the ceiling along with a 3 Amp PoE power extractor for 5 Volt out and ran a CAT-5E cable through the attic to the nearest PoE switch. Wife doesn't even notice it in the closet, and I can still get to it.

BTW, the roof sheathing product with foil I mentioned is TechShield LP. Se: LP TechShield Radiant Heat Barrier | LP Building Solutions (lpcorp.com) I am bringing this up again for new feeders who have outdoor antenna mounting limitations (Condo, HOA rules etc.) and may have metal in the roof that makes antenna mounting in an attic a no go. TechShield is installed with the foil face down, and is an OSB product, not a true plywood. Sometimes the voids between the roof trusses are also filled with fiberglass bats (which may also have a foil facing), so you won't see the foil on the TechShield. In this roof condition, the FG batts are usually installed on the ceilings above living spaces between the bottom chords of the trusses. Here in Hawaii, typical framed houses have TechShield, covered with 30# roofing felt or for higher performance roofs a synthetic commonly called "shark skin", or EPDM rubber "peel and stick" and then a higher performance asphalt shingle.
Happy Feeding!

 

I'm going to add some reflective tape for testing.

 

Hey Kuunanet, I'm going to order the cable and antenna tonight so hopefully I'll have them in time for the long weekend. For now, I've moved the rig from the attic back to the 2nd floor to test out another window location. Big decrease in range, so the attic is the way to go for me. My setup will be similar to yours, except for the indoor antenna, with a discreet hole in the ceiling of my den for the coax and the Pi tucked away in a corner. I may add PoE later bur for now a plug and the Pi's wifi seems to be doing fine.

My feeder ID is j3Tvt-TgF9UB, but the feed at the moment is pretty sad (1 airplane as I type this). I'm only getting 30-50nm and not much at very low altitudes. It will improve a lot once the bigger antenna is installed. Even with the kit antenna, I was getting 50-125nm, sometimes more from the attic, and down to ~600' altitude at the local airport which is a good 20km away.

I'll post an update in a couple of weeks once it's all set up.

 

I'll look in then. Happy Feeding! Are you near any interesting airports or CAF bases?

 

James, You have a TechShield roof? Watcha gonna test?

 

I'm in a sort of interesting location.

The local airport (Ottawa) is an international airport but the international flights are fairly limited (Toronto is only a 45min flight and is the main international hub in the east, followed by Montreal which is about a 25min flight away). Mostly short hop flights to the US hubs in the northeast (NYC, Chicago, DC, Philadelphia, etc.) and a few regular flights across the Atlantic (Frankfurt & Heathrow being the most common). A fair number of domestic flights and vacation flights to places like Cancun, and a couple of cargo terminals. There's also a medivac helo (A139) and turboprop based there.

CFB Trenton, which is one of the larger Canadian military airports (houses C-130s, C-17s, SAR helos and some VIP aircraft) is about 100nm away, but it's in the direction where I have obstacles limiting my range. I'm hoping the better antenna will see that far.

Montreal Trudeau airport (aka Dorval) is a similar distance in the other direction. I was getting spotty coverage of it with the kit antenna when the rig was in the attic so I will hopefully get decent coverage of it with the new antenna.

Also 3 smaller airports for private aircraft and Montreal MIrabel (where they finish the C-series/A220 and have a cargo hub) are within range.

I'm also near the air routes from Europe to Toronto, Chicago, Detroit and probably a few other hubs in the midwest and the routes from the east coast (NY, DC, Boston, etc. I assume, haven't pulled up flight plans yet) to Asia.

All that to say, even with the little antenna I've seen a broad spectrum of airlines and aircraft types, and a few USAF transport birds heading to/from Europe.

 

Should be some good spots there. BTW have you tried Hey What That yet? Here is a sample of where my remote feeder will probably go. HeyWhatsThat You should do this for your location. Fun to play with too.

 

I have tried Hey Whats That. I used it to get my location & elevation for the feeder software. My experience (so far) is that it only accounts for terrain, not structures, so it reports artificially long theoretical ranges for me. But it's interesting to get an idea of what could be possible for range.

Love your location. You must see lots of traffic from the airport and military bases nearby.

 

Sadly, It's not on that hill yet...... but even with the temp feeder on my roof, I catch a lot of military traffic from NGF.

 

Well, I finally go the antenna permanently installed. Life and the dericho that blew through Ontario a couple of weeks ago delayed me a bit. Now getting from ~100nm in the obstructed direction to 150-200nm in the unobstructed directions. Seeing 20-50 aircraft most of the time. Local small craft round Ottawa, a lot of the regional flights for eastern Canada, and the main air routes from Europe to the midwest, middle east to midwest & west coast, and east coast to Asia. Not much military traffic. CFB Trenton and Fort Drum NY are at the limits of my range, but the occasional cargo plane out of Tenton or UH60s playing around Ft. Drum show up.

Here's a photo of the installation for anyone who is interested:

 

Looking good.