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Originally posted by gregy View Posthello ABCD567
reference your post #1391
can you pls confirm if this design is for 50 or 75 ohm?
from the SWR plot it would suggest that its 75ohm
Q: do the dimensions as shown change for 50 ohm? (im using 50ohm coax cable before/after 50ohm masthead LNA)
If dimensions are different - is it possible to indicate these?
thanksOriginally posted by abcd567 View PostYes, the design is based on 75 ohm system, but using it on 50 ohm system will not cause any big loss in performance.
I did not try how this design matches with 50 ohm. Maybe just moving the cable tap few mm will tune it for 50 ohms system.
Give me some time to go through the simulation /modelling to workout the 50 ohms dimensions, if different.
The Gain & Cable Tap position are same as for 75 ohm.
SWR is a little bit higher i,e for 75 ohm it was 1.52, and for 50 ohm it is 2.08.
SWR can be reduced if the Matching stub gap is reduced, but it is difficult to achieve narrower gaps and sharper bends with a thick wire of 3mm dia.
Please see the simulation Results for 50 Ohm system:
franklin-50 ohm-4E-3mm wire-6mm gap-round bend-gain-pattern.pngLast edited by abcd567; 2014-08-31, 03:19.
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NEW ANTENNA - THE COILED DIPOLE
STEP 1 - MODELLING & SIMULATION
STEP 2 - CONSTRUCTION
STEP 3 - TRIAL RUN
The the Camera Flash has created shadows of coils on the blinds, making coils look like double helix, with much more than actual number of turns.
Last edited by abcd567; 2014-09-02, 17:09.
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Originally posted by peterhr View Postand now the amplified coiled dipole?
Have done trimming of 1/2 wavelength dipole.
The dipole limbs were trimmed in steps of 3mm, then put to trial run after each trim. Started from 69mm, went upto 60mm. As the length was reduced, range reduced, the number of far away planes reduced, and number of nearby planes increased.Last edited by abcd567; 2014-09-03, 20:33.
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Originally posted by lexj View Posthttp://www.ebay.com/itm/138MHz-4-4GH...3D331238989847
Source:
http://www.qsl.net/n9zia/elecraft/n9zia.pdf
[ATTACH=CONFIG]4694[/ATTACH]
For more info:
http://forum.planefinder.net/threads...-a-filter.135/
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same ebay shop has one of these,
you will need this to do your tuning. You can get directional couplers from many places
watch this video (the first i found) you could in theory use the DVB-T dongle as the spectrum analyser this would then allow you to tune aerials.
Use a RF sweep generator, a directional coupler, and a spectrum analyzer to tune a 2.45 GHz antenna.The directional coupler is RF Power SDC-202-302-R1-8 and ...
Food for thought for doing this at home myself.Last edited by SpaxmoidJAm; 2014-09-04, 20:52.T-EGLF8
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Originally posted by SpaxmoidJAm View Postsame ebay shop has one of these,
you will need this to do your tuning. You can get directional couplers from many places
Use a RF sweep generator, a directional coupler, and a spectrum analyzer to tune a 2.45 GHz antenna.The directional coupler is RF Power SDC-202-302-R1-8 and ...
watch this video (the first i found) you could in theory use the DVB-T dongle as the spectrum analyser this would then allow you to tune aerials.
Food for thought for doing this at home myself.Last edited by abcd567; 2014-09-04, 20:57.
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it might need a lot playing to get it to work mind but that's half the fun.
www.mini-circuits.com have a lot of RF stuff not the cheapest but they are good. I will look tomorrow to see which coupler i brought, they have a bewildering amount of stuff.T-EGLF8
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DIPOLE LENGTH vs. RADIATION PATTERN & GAIN
As shown by the above animation, the full wavelength dipole has a combination of high gain and a horizontal pattern which is most favourable for ADS-B, but has the disadvantage of very high impedance, which requires impedance matching arrangement (stub, coil etc)
The 1.25 wavelength dipole is also similar to full wavelength, and has slightly better directivity in horizontal direction, & lower impedance than fullwave, hence easier to match the impedance. It Is very popular as 5/8 wavelength whip with ground plane (the 1.25 wavelength dipole is two limbs of 5/8 = 2 x 5/8 = 10/8 =1.25).
The 5/8 wavelength whip with maching coil at bottom is a popular whip for mounting on vehicles, where metallic body of the vehicle serves as ground plane.
Last edited by abcd567; 2014-09-05, 11:56.
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[BOriginally posted by SpaxmoidJAm View Postit might need a lot playing to get it to work mind but that's half the fun.
www.mini-circuits.com have a lot of RF stuff not the cheapest but they are good. I will look tomorrow to see which coupler i brought, they have a bewildering amount of stuff.
.
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