best antenna

[abcd567]

Can anyone else here... just out of curiosity... use SDRShape.exe for Windows and test your 1090 MHz income freq and see how close it is to 1090 if not dead on. And mention which SDR dongle you use.

I for one have been using Nooelec R820T SDR &DVB-t ver 2 ($22.99 US ) and also 3x DVT-T + DAB +FM (R820) also ($12.00 US). All 4 brought from amazom.com

I am using (all from eBay):
1) 2 x Nooelec Newsky v2 RTL-SDR DVB-T+DAB RTL2832 (Receiver chip) + R820T (Tuner chip). Each Canadian $22.60 (cost+shipment+sales tax).

2) 1 x KDQ23 NEW RTL-SDR FM+DAB DVB-T Dongle Stick RTL2832+ R820T SPC-155. Each Canadian $ 9.94 (free shipment, no sales tax).

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[Rooster]

....

I removed amplifier & power injector and ran two tests (1) with transformer & (2) without transformer. The range with transformer is far less than range without transformer. This is contrary to my expectations! Cannot make out the reason. Can anyone explain why?

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I'm thinking that maybe your transformer is resonant, and either acting as a tuned circuit, or is very "lossy"
It's very difficult to be accurate with inductors at this frequency.

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[andyk1]

I have 2 from Nooelec $26 cost+shipment aproximately+ 1 from China $10 cost+shipment. I did not notice any difference in performance. I have SDR#. I use it to listen FM on my computer . Please tell me how to use it to measure antnna frequency.

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I think It's the same program. Mine looks like this. (See attachment). In the waterfall just below the red line is the center of my receiving (In Coming) 1090 freq which you can see is not dead on. This is from my NooElec SDR Dongle.

SDRSharp1.jpg

[andyk1]

I'm thinking that maybe your transformer is resonant, and either acting as a tuned circuit, or is very "lossy"
It's very difficult to be accurate with inductors at this frequency.

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In Dump1090 (Raspberry Pi) I could not use the auto gain's. I.E. --AGC on and -gain 32.9 was the only way to get good performance. Others have stated they only needed auto gain and it worked for them In Windows using RTL1090 all auto gain settings worked best (for me) It was a lot of back and forth testing in Dump1090. For me I get my optimum signal using a amp at the mast head. Lose distance and coverage area without. I have no idea why.

[abcd567]

I think It's the same program. Mine looks like this. (See attachment). In the waterfall just below the red line is the center of my receiving (In Coming) 1090 freq which you can see is not dead on. This is from my NooElec SDR Dongle.

[ATTACH=CONFIG]2990[/ATTACH]

Yes, SDR# & SdrSharp are two names of SAME software. There is a setting by which freq error can be adjusted.

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[abcd567]

I'm thinking that maybe your transformer is resonant, and either acting as a tuned circuit, or is very "lossy"
It's very difficult to be accurate with inductors at this frequency.

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It is an air-core auto transformer, so it cannot be lossy. See attached pictures.
uploadfromtaptalk1385758091434.jpg uploadfromtaptalk1385758136097.jpg uploadfromtaptalk1385758176504.jpg

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[andyk1]

Yes, SDR# & SdrSharp are two names of SAME software. There is a setting by which freq error can be adjusted.

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Um yes. This is set to zero adjustment in SDR# or SDRShape to see how far off actual is . I have to offset this in Dump1090 with the --freq 1089.****** command and I forgot the commandline setting in RTL1090. Command line switches can be found at http://rtl1090.jetvision.de/ I think or somewhere at this website. Sorry, no time to look it up but am sure a search with find it.

[abcd567]

Um yes. This is set to zero adjustment in SDR# or SDRShape to see how far off actual is . I have to offset this in Dump1090 with the --freq 1089.****** command and I forgot the commandline setting in RTL1090. Command line switches can be found at http://rtl1090.jetvision.de/ I think or somewhere at this website. Sorry, no time to look it up but am sure a search with find it.

Do not adjust rtl1090 frequency. There is nothing wrong with rtl1090. This is ERROR in SDR# DISPLAYED FREQ vs ACTUAL FREQ.
Have you tried another software "ADSB#" as an alternate to "RTL1090"?

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[Rooster]

Do not adjust rtl1090 frequency. There is nothing wrong with rtl1090. This is ERROR in SDR# tuning DISPLAY FREQ vs ACTUAL FREQ.
Have you tried another software "ADSB#" as an alternate to "RTL1090"?

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THANKS! thats what I've been saying all along :-D

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[abcd567]

I'm thinking that maybe your transformer is resonant, and either acting as a tuned circuit, or is very "lossy"
It's very difficult to be accurate with inductors at this frequency.

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Air-core, Auto-transformer. Total 12 turns. One end grounded. Other end (12 turns) connected to antenna. Tap at 2 turns from grounded end, connected to feed coaxial/receiver. Turns ratio=2:12=1:6; Impedance ratio= squre of turns ratio=1:36

Coil dia D=9mm
Wire dia d=0.5 mm
Coil length l=24mm
Number of turns n=12
uploadfromtaptalk1385767102541.jpg

Calculated:
L=0.44 micro Henry
X=3045 ohms
R=208 ohms
C=0.42 pF
Q @ 1090Mhz = 14.6
Self Resonant Frequency=387 Mhz
uploadfromtaptalk1385767307255.jpg

Credit for calculator to hamwaves
http://hamwaves.com/antennas/inductance.html

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[Rooster]

Id definitely try to get that tap wire shorter.... maybe rotate the coil to allow this ? I'm still not convinced on the resonant frequency of this thing - the coils is a "long" way from the earth plane, so "C" could be anything !

Cant you construct an antenna without the need for impedance matching ? Would make life a LOT easier ;-)

[abcd567]

Id definitely try to get that tap wire shorter.... maybe rotate the coil to allow this ? I'm still not convinced on the resonant frequency of this thing - the coils is a "long" way from the earth plane, so "C" could be anything !

Cant you construct an antenna without the need for impedance matching ? Would make life a LOT easier ;-)

I will try to shorten the tap wire. The calculation of C is based on only inter-turn capacitance & assuming away from ground, so the calculation is accurate.

I have made dipoles 1/2 wave, full wave, 5/8 wave, 1/2-over-1/2 franklin, 3.5-element shorted Coco, and latest 3.5-element+1/4 wave whip, no short CoCo (on trial run at the moment).

Best result without Amplifier: 1/2 wave dipole, the shortest & cutest antenna I have made uptil now. Number 2 is Coco with short. Number 3 is Franklin half-over-half.

With amplifier, FRANKLIN is #ONE. The 1/2 wave dipole & CoCo are #2, more or less same. That is why I am keen to find out why Franklin is so bad without Amplifier.

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[Rooster]

do you have a link to the Franklin antenna please ?

[abcd567]

do you have a link to the Franklin antenna please ?

There were many links. I will search and send you this week end. Right now I have only this link. Download pdf document and see last figure (figure3) on last page (page 4).

http://www.aktuellum.com/circuits/an...nts/242342.pdf

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[abcd567]

do you have a link to the Franklin antenna please ?

Another link. Download pdf. It shows Coco has evolved from Franklin

http://www.para.org.ph/membersarticl...iques - 21.pdf

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