Maximum Range - sometimes you have to settle.

FlightAware ADS-B Flight Tracking
1

Running a custom cut spider, after testing a discone, cantenna, co-linear, 5/8 vertical, vertical dipole, and a fractal, running the latest software on a Pi3 with a prostick plus, this is as good as it’s likely to get.

http://www.vocshop.com/rick/VirtRad.png

Why? 60 and 70 foot oak trees in my and the neighbor’s yards. Aka “GIANT BAGS OF WATER HANGING IN THE SKY”

there is some hope things may improve when more of the leaves fall off for winter…

You can see that I can see further towards the horizon in a few directions that are the gaps between the trees…

Oh well.

2

Why not use one of the tall oak trees as your antenna mast?

https://farm6.staticflickr.com/5582/30029624212_f640356a6f_o.jpg

3

Tell you what… YOU come climb one of them with a fiberglass pole and some straps.

Bye the way, that is not an oak. Oaks sort of lack that central trunk with lateral branches.

Still, drop by. I’ll provide the pole.

4

Another modest suggestion for improving your range is ‘move’. :wink: Tree in the front yard cuts low level traffic in all but winter.
In the foothills East of Sacramento I have hills to cut as well. In support of the ‘move’ suggestion, I ran a couple of cross-country ‘experiments’ in the last couple years. sitting next to KSLC proved that the poor home town results weren’t due to a badly done homegrown coco. On a hilltop just South of Santa Fe NM, the FA antenna picked up a record around 400 mi.
Still, there’s no place like home, Toto. :slight_smile:

5

Move is inevitable… my wife is less and less accepting of the winters here. Also the proximity of the trees to the house and the way that a power line cuts across the back yard only 25 feet from the house makes hanging HF wire antennas difficult, and my wife refuses to let me put beams on the roof. :frowning:

6

Move is inevitable… my ***wife ***is less and less accepting of the winters here. Also the proximity of the trees to the house and the way that a power line cuts across the back yard only 25 feet from the house makes hanging HF wire antennas difficult, and my ***wife ***refuses to let me put beams on the roof. :frowning:

Wives have a lot to answer for :unamused: Are there any ladies on this forum or are we all sad blokes :wink:

7

Where/how is your antenna mounted? I have a similar situation with trees, I think. That is REALLY short range. This has to be something some of us can help you solve. I started less than a year ago with junk antennas inside of a house and one of the blue Nooelec dongles. Ive been through a few antennas, setups and locations and I’m still looking to tweak my setup.

List your equipment and setup. Maybe there is something being overlooked. I see this stuff as a challenge and it’s very gratifying every time improvement is made.

Here is my current setup in order:
RPi 2 model B
FA orange dongle
SMA to type F adapter - 6"
40 feet of quad shield RG6
F to N adapter
FA 49" antenna 35 feet in the air on a 5 foot stick on a 30 foot tower.

I had a FA filter but took it off and gained a little.

My second receiver is at work in my office inside of a metal building. It’s an old Dell laptop running Win XP with the Nooelec blue dongle, an adapter, 5 feet of generic RG6 and a cantenna. It runs 1090 mutability and PlanePlotter. Tomorrow I plan to test a cable tv amp I found. It says it goes to 1 Ghz and 15db. It will either help or hurt. One way to find out. LOL

8

@zeek70706

I have bad experience with TV amplifier, and also with satellite amplifier having 47 Mhz lower frequency limit. With these amplifiers, the performance dropped.

I live in urban area with strong on-the-air tv, fm, air band, taxi, cell phone and other communication channels, all between 47 mhz and 900 mhz. Both the tv amp and the satellite amp with 47 mhz lower limit did amplifiy adsb, but also amplified all these signals, saturating/overloading the dvb-t dongle.

When I used a satellite amplifier with 950 mhz lower limit, my max range and plane count almost doubled.

If you live in an area of low tv, fm, cell phone signals, the tv amplifier may improve your reception. It all depends on location. No harm trying a tv amplifier if you got one.

9

http://flightaware.com/adsb/stats/user/zeek70706#stats-24043

I installed the TV amp at 8am this morning and has definitely helped. The main problem is the location. Based on anther thread, this building has to be as bad as a mobile home trailer which shows a loss of 20-25 db. The amp helps but just does not get much to amplify. I doubt I will ever be able to improve the antenna location, but I am not giving up.

10

Rpi3
FA Prostick Plus (helped a lot)
custom cut spider (1/4 wave vertical with 8 downsloping radials) 23 feet in the air on the northeast corner of the house.
(Higher is essentially impossible, sorry.)
28 feet of quad shield rg6
F to sma adaptor - one piece, no coax.

11

Your 50 mile counts are as good as mine but beyond that drop off dramatically. The Prostick does give a nice boost.

If you go to my page and pick a date before Oct 4, that will give stats when my cantenna was at 4 feet as in my picture to the left and with the FA filter.
http://flightaware.com/adsb/stats/user/zeek70706#stats-18102

I’m going to ask some questions that may seem stupid but that I have seen here in the forums cause issues for people.
Are you sure your SMA connector is NOT reverse polarity and has a center pin to connect to the Prostick?
I assume your spider is made from an N bulkhead connector. Does it and your cable connector match? 50 or 75 ohm.
Have you checked and rechecked all connections?
Are you sure no cable shielding is shorted to the center wire?

Just trying to think of issues I have seen others have.

12

Why are you using RG6 cable? That’s 75 ohm cable and everything else in the system is 50 ohm.

13

There can be many problems so let’s take them one by one:

  1. antenna - can you test it with a small cable run outside and see how it performs? I recommend a coco of 8-12 elements(it takes ~45 mins to build one from scratch), for me it was the best solution. If you are making a good antenna take care to isolate the joints, if water pours in your antenna then the performance is drastically reduced. Normally you should use a plastic pipe and put the antenna inside then seal the ends. On my antenna I have sealed the joints between elements with a special rubber and that helped a lot.
  2. cable run - long cable runs introduce a lot of signal loss, for RG6 cables the attenuation is around 3dB / 50 ft(15m). That means that you loose half of the input power if the length is 50ft. An amp is ok but the amp also amplifies the noise so the signal quality is reduced. Also not any amp is a good choice, you should check the band that is amplified, the TV amps I’ve tried had poor performance on 1.1GHz.
  3. antennas nearby - in my case on the roof of my building there is a GSM site! So I had to install the antenna behind a closet, that closet is made of metal and reflects the gsm signals so my receiver is not saturated because of that. I’ve lost 120* of clear skies because of that but the reception is great.
  4. band pass filter - this is really useful in areas where there is a lot of rf emission
  5. imperfect contacts - you have to take care on all the places where your cable is interrupted and jointed with rf elements, the contacts have to be good else you will have a lot of power loss inside that places. Also reduce the number of joints, try to make all the cable run from one single piece.
  6. the setup on your receiver - i have a piaware setup and the amplification of the receiver it’s not set at maximum, I have a better performance with a smaller gain.
  7. geography - normally what you see with your naked eyes from the place where antenna is mounted should be also visible to the antenna so you should take in account the buildings, hills, mountains, etc. that are nearby and obstructs the antenna view.

My setup now is 12 elements coco, ~40ft(13m) of cable run, band pass filter, pro stick, 2m usb cable, pi3. All works smooth, ~700mgs/s and max ranges ~250+mi.

14

Good point. I’ll swap a length of 58x in come spring when I can reach the bottom of the antenna without fear for my life.

15
  1. Been there, done that. Each antenna I’ve built ran for a week, six feet above ground, just outside the window where I have my equipment bench on a 10’ piece of rg58x. The spider did as well as any of them, and my 10 element coco (actually, the third 10 element coco, since those are tricky to build exactly perfectly) wasn’t any better.

Regarding water… you know, I’ve been building antennas since I was 13 when I got my novice license in 1968. I’ve used everything from latex house paint to self-sealing tape, to silicone to sugru to seal active elements. You —do— understand that only the active element needs to be sealed right? The radials don’t care. Think about all those beams and tv antennas out there. The passive elements of an antenna (and in this case the downsloping radials) don’t need to be protected, nor do they need to be connected to anything.

  1. The antenna is 23 feet in the air. The bench is inside the basement window and the rtl-sdr is at the end of 28 feet of coax. Really, Without putting the rtl in a sealed container up at the antenna, it can’t be any shorter… TV amps generally do little or nothing at 1 ghz, and if I was going to add another amp (since the prostick plus aleady has one) it would need to be up at the antenna… which I could do, but not till spring.

  2. well, ignoring the HF dipole going from the house eve out to the oak tree in the front yard, the nearest cell tower is about 3/4 mile away, and again the prostick plus has a quite good filter. It helped a lot. My 2 meter and 440 MHz jpole are on the other side of the house.

  3. Built into the psp.

  4. See comment 1. Total dc resistance from the antenna to the radio is on the order of milliohms.

  5. I admit that I haven’t experimented with the software gain settings…

  6. Geography. Well, that is the problem.
    http://www.vocshop.com/n0oxf/house.png
    The antenna is at the peak of the roof at the point marked X in red. The yellow circles are sixty to seventy foot oak trees. The green circles are 50 foot maples. In addition, you can’t tell, but I am half-way up a small hill. The houses and trees at the west end of my block are 30 feet higher than my house so the western horizon from the antenna is elevated about 18 degrees.

The orange line is a utility line with power at the top, then phone, then cable tv running down the center of the block across the back yards. (which is what prevents me from hanging decent HF antennas out back where I want to. Instead, I have to use the trees in the front as supports. Oh well.)

It is now winter, and we’ve had wind and rain the last week or so, and most of the oak leaves are gone. My overall range has more-than-doubled. It will fall back in spring. If I was prepared to put up a 60 foot mast, which my wife won’t allow, things would be different.

16

The F to SMA converter is a single straight through piece. There is DC continuity in the shells and in the center conductor.

The spider is built on a double-female F connector, which was stupid since the Prostick Plus is 50 ohms. So, I’ll build another on an SO-259 panel connector and use 58x when I get out the "Really long ladder) to work on the eves in the spring. For now, yes, I have a 75 to 50 mismatch at the prostick plus.

The dc continuity from top to bottom is milli-ohms, and is open-circuit unless intentionally shorted, tested when I installed the antenna, so nothing shorted.

17

I think most people build spiders from N bulkhead connectors and the only reason I mentioned it is because the 50 and 75 ohm N connectors have a different size pin which causes issues if mixed.

I just listed issues I have seen in the past year I have been on this forum.

18

I’m using because I have a spool of it from building a house and from what I have read here, it makes basically no difference for a receiving only setup. However, my goal is to mount my prostick directly to my antenna to eliminate such issues and the loss I have from 40 feet of cable.

19

At an early stage of their development, the wireless communication systems (HAM, CB, Police, Fire, Walki Talkies etc) standardized on 50 ohm impedance.
Later inventions of Cell/Mobile Phone and WiFi also followed the suite and adopted this system.

The free to air TV originally had 300 ohm system, and used 300 ohm receivers, 300 ohm antennas & 300 ohm twin-lead between antenna & receiver. With advent of Cable TV and Satellite TV, the standard changed to 75 ohms, and is the current standard for TV.

The Receiver we use for ADS-B receiving is DVB-T i.e. “Digital Video Broadcast - Terrestrial” and is therefore designed as a digital TV receiver. It therefore has an input impedance of 75 ohms (see schematic below).

If DVB-T receiver is used with a 50 ohm antenna and 50 ohm coax, there is a impedance mismatch at the receiver-coax interface.
If DVB-T receiver is used with a 50 ohm antenna and 75 ohm coax, there is a impedance mismatch at the antenna-coax interface.

As far as I know, the ProStick’s front end rf pre-amplifier has 50 ohms input/output impedance, and there will be no mismatch if 50 ohm coax and 50 ohm antenna are used. However there is a hidden mismatch: the RTL chip inside is still 75 ohms, and pre-amplifier is 50 ohms, so there is an internal impedance mismatch (unless Flightaware has included some sort of impedance matching circuit between pre-amplifier and RTL tuner chips).

Apart from all above discussion, the effect of 50 to 75 ohms mismatch is negligible, as shown below.
The impedance mismatch between 50 ohm & 75 ohm results in:
reflection coefficient 0.2
vswr 1.5
mismatch loss 0.177 dB
power reflected 4%, power reaching the load 96%.

When 50 ohm mixed with 75 ohm,
Reflection Coefficient Γ = (75-50)/(75+50) = 0.2
VSWR = (1+Γ)/(1-Γ) = (1+0.2)/(1-0.2) = 1.2 / 0.8 = 1.5
Mismatch Loss in dB = -10 log (1 - Γ²) = -10 log (1 - 0.2²) = -10 log 0.96 = 0.177 dB

Impedance mismatch is important and costly in case of transmitters as power transferred from transmitter to antenna is in tens or hundreds of watts. In case of receiving, power transferred from antenna to receiver is in micro watts, and the loss is made up easily by front end amplifier or the tuner/receiver chips.

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20

Well, you should hang the antenna on a tree top, I don’t see any other viable option for you right now. The leaves of the trees contain water that is a really good signal damper. Other idea is to install the receiver somewhere else, if you have a friend that has a better sight to the sky and lets you install your receiver you can try to install it there.

About the gain of the receiver, I have configured dump1090 with gain -10 , this is the autogain and it does a really good job, you will always have the best reception possible according to the developers of the software. Also check for ppm to center the reception, mine is around 8, you can do it with gqrx or other spectral analyzer.

/usr/bin/dump1090-fa --device-index 0 --gain -10 --ppm 8 …
This is how the ps ax looks for dump1090 on my pi.