Antenna


#1

Newbie hear, making an antenna

I’ve look at tons of video on how to make a ads-b antenna and I’m ok with that,

My question is what type of connectors do you need to connect the anntena to the rg6 cable
then from the rg6 cable to the dvb-t+dab+fm usb dongle.

Like the F-type connector or UHF Female Jack To MCX Right Angle Male connector

thanks
andre


#2

Whatever matches what you have … I use twist on F connectors for simplicity.


#3

yes ok for the f connector for 1 end , but what is the other end that connect to the dvb-t dongle.

its like 1/8-1/4" in size…


#4

After purchasing DVB-T dongle, the very first thing you should purchase is a pigtail, with MCX male pin at one end (for dvb-t) and F-female connector at other end to connect regular antenna coax (RG6, RG58 etc).

The MCX male connector of pigtail is delicate, and sometimes breaks. Better order 2 pigtails, one in use, one spare, to be immediately available if mcx connector of one gets damaged. These are not costly ($3.80 + free shipping from China)

http://thumbs3.ebaystatic.com/d/l225/m/mdrImDH82MNX8tYr1OYk0sA.jpg
http://ebay.com/itm/F-female-nut-bulkhead-to-MCX-male-RG316-cable-jumper-pigtail-15cm-/320847773379

http://thumbs4.ebaystatic.com/d/l225/m/mnn821kGZ8JMM1I-6zITnuw.jpg
http://ebay.com/itm/RG174-6inch-RF-pigtail-F-TV-female-jack-pin-bulkhead-to-MCX-male-straight-Cable-/251399601339

**Please also see this post:

http://discussions.flightaware.com/ads-b-flight-tracking-f21/3-easy-antennas-for-beginners-t20177.html**

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#5

I’m getting better reception with a homemade dipole than with an 8 element coaxial collinear. Maybe it was my workmanship on the collinear but I had no shorts and continuity. It was sure a lot quicker to build the dipole. I just stripped back 140 mm of RG6U coax to bare center conductor. Then I put heat shrink tubing over the bottom 70 mm. Next I jammed a bare copper wire between the shield and dielectric and put an outer 70 mm shrink tubing over it and the already covered center conductor. Cut that wire to match the coax center conductor at 140 mm and bend each side 90 degrees at the end of the tubing for a total dipole length of 140 mm. Mount vertically and enjoy. I’ve also got an in-line amp installed that helped quite a bit.


#6

A half wave dipole was my first DIY antenna. It had two limbs of 1/4 wavelength (each limb = 68 mm). I fitted it with an amplifier also. It was made 2 years ago, and I posted the details & photos in:

(1) Planefinder forum http://forum.planefinder.net/threads/ads-b-diy-antenna.23/

(2) Flightradar24 forum http://forum.flightradar24.com/threads/3831-best-antenna?p=38188&viewfull=1#post38188

After the 1/2 wave dipole, I have experimented to design & make many other types like Franklin Collinear, Coaxial Collinear, Wire Collinear, Cantenna, and Spider. All these experiments are recorded in the above two forums.


#7

Thanks for all the info…


#8

Based on your experiments, what do you think is the most successful antenna ? The cantenna seems to have the best gain, but I am unsure on how to properly interpret the gain plots to see if that’s the only data point for comparison.


#9

It is not only Gain, but also SWR which matters. If the SWR is very high, a high gain antenna may perform poor. Generally an SWR of 1.5 or less is considered decent.

The best antenna is not same for everyone. It is the combination of antenna, it’s location & other components of the system which decides which antenna is best in any particular setup.

For some users, Spider has proved better than Cantenna, while for some others Cantenna has proved better than Spider. At the best it can be said that Cantenna & Spider are close contenders, but which one is best under a particular situation can only be known by making & trying both.

The CoCo performs better than Spider & Cantenna if made correctly, and that is a big if :frowning: :open_mouth: :confused: :angry: .
CoCo is very alluring. It looks so simple & easy to make, and claimed to have high gain. The problem shows up only when it is made & put to trial. For most CoCo makers, their first DIY CoCo gives performance far below what was expected or claimed. Only few lucky ones have their first CoCo give good performance.


#10

What contributes to a high SWR, is it something to do with impedance? ( = on paper, this aerial performs really well but yo need to match it to a cable and reciever of - say - 1.5k-ohm - which you won’t find anywher)

Would putting an amplifier with a high impedance input help?


#11

Yes, it is impedance ratio between antenna & system (receiver/coax/amplifier) which determines what fraction of the signal picked by antenna will be transferred to the receiver. Maximum signal transfer takes place when impedance of antenna = impedance of system. Under this condition SWR=1. Actually SWR is an indicator of signal transfer & impedance matching. Higher the SWR, higher the mismatch and lower the signal transfer. SWR 1.5 or less is considered decent as this is the range where major portion of signal transferes to the receiver.

Using a high INPUT impedance amplifier with a high impedance antenna will help, provided OUTPUT impedance of amplifier is 75 ohms and matches the 75 or 50 ohm coax/receiver.

Even using a normal sattelite amplifier (having 75 ohm input & 75 ohms output impedance), with a high impedance antenna also helps. Due to impedance mismatch between antenna and amplifier, the antenna transfers same reduced amount of signal to amplifier as it transferes to the coax/receiver without amplifier. The amplifier’s large gain boosts the reduced input signal to even higher than the full output signal of antenna. Since amplifier & coax/receiver are impedance matched (i.e. all are 75 ohms), maximum signal transfer takes place betwee amplifier and receiver. The receiver as a result gets signal even higher than maximum signal of the antenna.

I have tested this with Franklin antenna WITHOUT the impedance matching stub (i.e. the stub in the middle to which coax is connected).

Franklin without impedance matching stub is a high impedance antenna, about 400 to 600 ohms. This is a gross mismatch with 75 ohms coax/receiver. Without amplifier & 12 ft coax, It gave me max range below 100 nm. With an amplifier & 12 ft coax, its range jumped to over 200nm, and number of planes more than doubled.
.


#12

Below is a table showing SWR vs Transferred voltage & power.

In case of a Transmitting antenna, it is the power (watts) radiated which is important. The radiated power is directly proportional to power transferred to antenna. Hence it is the power (watts) transferred to antenna which is important & is the criteria for transmitting antennas.

In case of a Receiving Antenna (our case), it is the voltage transferred to receiver or amplifier which is the criteria. This is because the front end of Receiver or Satellite Amplifier (to which antenna is connected) is a pre-amplifier which is a voltage/current amplifier. Hence for ADS-B Receiving purposes, it is the Voltage transferred (yellow highlighted columns of the table below) which is important and applies.

Please see the photo below. The Satellite amplifier’s output is rated in microVolts, not in microWatts.


#13

It’s great that you’re going to the effort to produce this type of thing, but maybe you can pick one thread and post there rather than posting the same thing in several places?


#14

Thanks Oliver for the suggestion. Yes I used to do the way you mentioned, and still my most of post are at any one place. However some posts are useful for many threads. Since only a few members brows all active posts, a large number will miss the post if posted in one thread only.

The above post was answer to member @PeterHR 's question in this particular thread. After preparing & posting the SWR table, I felt this is of interest to two other threads also, so I posted it there also for those who dont brows this thread.


#15

I have done an experiment to demonstrate the negative effect of high SWR. Details & pictures/graphs are given below.
Note: I have used RRD Tool /Collectd to plot the performance graphs. Thanks to Oliver Jowett (@obj) for adding the functionality in dump1090-mutability, and to @Xforce30164 for providing auto-install script with very useful tweaks.

I made a Spider and a Franklin-Spider. Simulations gave following results:
Gain: Spider = 1.7dBi, Franklin-Spider = 3.5 dBi
SWR: Spider = 1.4, Franklin-Spider = 2.0

When put on trial run, in spite of Spider having much lower gain than Franklin-Spider, it out performed Franklin-Spider. The reason was not obvious till I added an impedance matching network to Franklin-Spider, bringing it’s SWR down, and then Franklin-Spider out performed the Spider. Please see simulations & photos below.

Image 1 of 6 - COMPARISON GRAPH

Image 2 of 6 - SPIDER

Image 3 of 6 - FRANKLIN-SPIDER

Image 4 of 6 - FRANKLIN-SPIDER (WITH IMPEDANCE MATCHING NETWORK)

Image 5 of 6 - SIMULATION OF SPIDER

Image 6 of 6 - SIMULATION OF FRANKLIN-SPIDER


#16

So post the full text once, and post a link to that post in the other threads if you feel the need.

Posting the full text to many different places means that all the replies get fragmented across the different threads, and irritates anyone who happens to be reading more than one thread. (Especially true if your post is more than a couple of lines - oh look, it’s another abcd page-long post full of antenna diagrams that I’ve already seen 3 times! Or are they slightly different here? I don’t know, I’ll ignore the post)