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JetPilot

Patch Antenna Coax Loss ?

38 posts in this topic

I am using a 14 dBI patch for my 2.4 GHZ receiver. The patch from BWAV, similar to the one seen here has a couple feet of coax and an SMA connector built onto it. Is there much loss with this white coax ? I am not sure what kind it is, but probably not the best...

I was reading the coax leingth versus loss chart on cyberflyers home page, and you would think that a commercial antenna could take that into account, but it seems unlikely to me that the peak would occour at a couple feet of coax that this antenna has. It sounds like more of a marketing choice than one tested for best performance.

I wonder if it is worth ripping into this antenna to take the coax out, and mount the receiver directly to the back of it ? I guess I would still need a couple inches of coax at least. Any thoughts on this ?

JetPilot

post-5-1181162818_thumb.jpg

Edited by JetPilot

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I've always assumed that if the guys are specialized in making antennas they should make them correctly, and never have really questioned it. I agree I haven't taken a very critical position here ;)

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I would be very tempted to shorten the coax to the minimum and fit a good quality connector.

Looking at the quoted figures for most aerials for this band I think they must quote for the aerial with no co-ax.

Terry

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as i said in rcgroups: yes

you should in my opinion cut the wire as much as you want.

wire is too thin, and you are losting dbi's

i don't know what kind of wire are they using with antenas but seems early an RG58, that got about 1 dbi of lost each meter, or maybe another with more lost, i don't know;

i just know that wire is very thin, and working at so high frecuency's, is better to keep wire as short as possible. and if it should be long, then FAT wire means better.

for them, adding a long wire of bad quality means they keep money, and they sell a 14 dbi but in facti it's just as "bad" as a 11 dbi...

standar sma connectors got a little lost too, from 0.1 to 0.5 dbi

i bet that the 8 dbi antena got a real efectivity around ~6 dbi

and same with the 14 dbi antenna

Edited by wallaguest1

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you will loose 1db pr meter,

so it is really bad with cables at 2.4GHz

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@ 860mhz a standard F connector clips almost 1db its also about 1db per meter at 860 on RG6 cable.

The only time I get a bad picture is when i fly outside of the antenna's specs or really low to the ground.

I dont see Horizontal lines to much but when I hate them.

I am going to pick up a couple of these units and try them out.

http://rf-links.com/ampr.htm

they also make inline amps for the tx side

These guys also make some really nice micro TX's check out the MX 4,5,and 6000's

I got a price when they were new and mx 4000 was around $500 to $600 canadian.

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There is a cable loss calculator - actually there are several, one of these is here:

http://www.ocarc.ca/coax.htm

This could help finding the proper cable and loss per lenght.

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the specs I have seen claim that the loss at 2.4ghz is greater for the connector than for a lot of cables, esp for a couple of feet of resonable cable. Unless you are going to solder a sma plug directly to the back of the antenna, I would think the risk of messing up the cable, would be greater than the gain, esp if the insulation isn't teflon. It can melt and change the spacing.

YMMV

Ken

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I am going to pick up a couple of these units and try them out. 

http://rf-links.com/ampr.htm

I just received one. According to Daniel the noise figure is crappy, so we'll see how it works out. Might not be worth the $150.

If it stopped raining...

Edited by Kilrah

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I had my patch cable cut down to just over a foot or so, or half the original length. The cable they use is high-frequency RG-58 variant I think. In any case, you should as a rule keep them as short as is needd.

Kilrah, the LNA works GREAT! Fantanstic performance I'm getting from it, no noise in my videos at all.

Daniel

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Kilrah, the LNA works GREAT! Fantanstic performance I'm getting from it, no noise in my videos at all.

Cool :D

Note to others: it's not the rf-links one referred to just above, that one still needs testing.

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Cool :D

Note to others: it's not the rf-links one referred to just above, that one still needs testing.

So which one is it then?

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I got the last one :-) sorry dudes hehe

I came early enough :P

Will be interesting to compare the 2 now :)

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for your convience :

http://www.webx.dk/rc/video-wireless/LNA2425/

now pictures of the inside stuff,

the 3 pin device SOT-89 with number 2GW is from Avago type ATF52189

it is narrow band matched to improve the NF beyond spec 1.6dB

yes it does improve range at super weak levels you can now fly longer away

with less TX power,

how much is up to your RX type, but I see improvement on all I have.

Edited by ThomasScherrer

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>So which one is it then?

http://www.rfbayinc.com/LNA/LNA-2425.pdf

I got the last one :-) sorry dudes hehe

Me too I came early enough. I previously has bought the LNA 2400 through ebay, but after reaching an agreedment with the seller I saw the LNA 2425 that looks quite better. Seller has accepted a change to 2425 paying him the difference :rolleyes:

Now a question would the LNA work fine with 2 receivers close each other in a diversity setting? Wouldn´t be worse for the receiver that doesn´t have LNA installed?

Edited by Wavess

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ok we was out flying today, nice nice,

the LNA really did also show improment on real flights,

how much is really hard to tell, I have to make more accurate experiments,

tomorrow I will bring this LNA to my work and measure its performance,

lets see then, real facts values to be revealed !

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real facts added to the page !

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WOW nice figures there, I can´t wait to have mine with me. You said you didn´t know how much the improvement was in real flight, did you tried putting 2 receivers close each other to see what happen?

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here we go, more results again online !

please reload !

you get with a Comtech receiver 4dB

same as if 500mW upgraded to 1.2W

or 10mW upgraded to 25mW

so it is not extreamly much extra ok I know.

but try to go from 10W to 25W that is expensive 4dB :-)

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numbers numbers numbers ! but how far can you fly with a 10mW or 100mW TX ? I want to see what it dose in the real world ;)

Terry

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well going 10dB up in power 10x will give you 3x range, rule of thumb.

so going 4dB up will only give you x1.4 the range you had before,

what ever that range was.

if you had 2000 meters before, you will achive 2800 meters with this LNA attached.

if you rx antenna or tx power is different, the range value wil simply change, but the x1.4 factor will remain, ok ?

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There you go again with the numbers !

I know the theory, I want to know what you get in real life. The numbers in the lab don't always work out in real life due to factors you had not thought of and calculated for.

I want to see how far you can fly on 10mW and a simple 8dbi patch to see how it compares to mine, saying it will give me x1.4 the range or whatever is no help. I don't believe it's that easy, will it add the same gain on a poor RX as a good one ?

I would rather see the distances obtained from your real flight tests than lab numbers.

Terry

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