cable connection for 2.4ghz yagi antenna construction

jackb9

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hello

i am attempting to make my first yagi antenna and have a few questions

a short pigtail is recommended to avoid signal loss. if i use RG-6 cable with low impedance, can a long run be permitted?

if i trim off the di-electric layer of the cable to accomodate a smaller connector, how would this affect the signal?

thanks
 

WA0CBW

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Look up the attenuation of the cable you are using to see how much loss you will have for the length you need. In general either the connector fits the cable or not. At 2.4GHz improper connector losses multiply quickly.
Bill
 

prcguy

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I don't think a 2.4GHz Yagi is a good choice for a first antenna project. The lead lengths from the coax to the elements are part of the overall element length, so they need to be very short as in a few mm at most otherwise any calculations for element lengths are off. How long of a cable run do you need? If your Yagi turns out to be 10dB gain, 100ft of RG-6 will loose 10dB of signal or all the gain of the antenna. You want to use a very short run or go to a much lower loss cable.
 

jackb9

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sorry for the late reply. i have been busy making the antenna. to keep the cable run as short as possible, i have done some improvisation. but have been unable to get the router(RP-TNC connector) to detect the antenna. so i do not know if the improvisation is the cause of the problem. kindly see attached photos and advise. thanks
 

MDScanFan

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I am all for home brew but as prcguy pointed out a yagi at 2.4 GHz can be tricky to get everything dialed in. UHF and below yagi construction is much more forgiving.

Have you considered buying one? On eBay you will find 2.4 GHz high gain yagis are plentiful and less than $20 with mounting hardware included.
 

jackb9

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MDScanFan said:
I am all for home brew but as prcguy pointed out a yagi at 2.4 GHz can be tricky to get everything dialed in.
hello thanks for your advice. i followed the guide from here:


looking at the photos of the actual construction, it seemed to be doable as the copper pins do not look to be machine fabricated. for a 20 element yagi, the theoretical gain is 17db.

i figured if i can get 5db, that would be a good start for improving along the way. now the problem is the router cannot detect the antenna at all. it would be impossible right? even a poorly made antenna should have some gain

so i would like to ask the coiling of the copper wire around the threaded connection, is it correct being the interface which the braided shield connects to?

thanks
 

prcguy

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Until this antenna is tested with something like an antenna analyzer its just a bunch of wire bits right now and may or may not work any better than a bunch of bits of wire. Looking at the driven element to coax connection, every mm of wire hanging in mid air like the ground side running parallel with the connector until it hits the connector is part of the driven element length and will change its resonant frequency.

Another problem I see is wood is a dielectric and will change the RF characteristics of wire passing through it. If a calculator says an element is supposed to be 400mm long and you stick a 400mm long piece of wire through wood it can act like a 450mm long piece of wire, etc.
 

jackb9

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WA0CBW said:
Did you solder the connections? If not that might help.
i tried to initially but the solder would not hold. which is why i resorted to making a loop.

for the braided shield which is tinned copper, and the centre conductor which is copper...do you have to use any special solder?

the wire is 2.5mm2. any advice on soldering them together? i tried with a soldering station putting out 450W

thanks
 

jackb9

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prcguy said:
Looking at the driven element to coax connection, every mm of wire hanging in mid air like the ground side running parallel with the connector until it hits the connector is part of the driven element length and will change its resonant frequency.
yes if i can get the solder to hold i would not making a loop in the first place.

prcguy said:
Another problem I see is wood is a dielectric and will change the RF characteristics of wire passing through it. If a calculator says an element is supposed to be 400mm long and you stick a 400mm long piece of wire through wood it can act like a 450mm long piece of wire, etc.
would PVC be a better choice then?
 

MDScanFan

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At 2.4 GHz the presence of any dielectric material along the length of the various elements will impact the electrical length to some extent. Without modeling it is is hard to tell how much of an impact.

In general, for a given material the less material the better. So, a hollow pvc pipe is better than, let’s say, a solid piece of pvc. The higher the dielectric constant of the material the larger impact it will have too. Wood has a dielectric constant around 2 and pvc around 4. So it may be a wash between the two options between solid wood and hollow pvc.

would PVC be a better choice then?
 
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