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Daniel Wee

Effectiveness of omni-directional whip?

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I was wondering if anyone here has pushed a whip antenna setup to the limit to see what kind of distance is realistic without resorting to patch antennas?

Right now, with my 2.4GHz 500mW TX and whip, and a Lawmate RX with whip, I've gone to over 1km (0.62 miles) without problems. However, I am not sure how far I can go with this setup. If some of you have gone further with this setup or with a 200mW TX similarly whip-antenna-equipped, can you post what sort of distances you have achieved? I'm just trying to get a ballpark figure for what to expect. Thanks.

Daniel

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I get ~500m with 10mW on a whip, goes to 1000-1200m with a 8dBi patch, ~3000m (but noisy) with the 14dBi with 15dB LNA.

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500m is good for 10mW, I only get 200m max and about 1000m with 500mW.

I would have expected better with the 8dBi patch though if you 500m with an omni. I can get 4x using the simple patch (800m max).

Terry

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I think I can probably go further with my whip on both TX and RX on 500mW. I think I'll try to push it a little further and see what happens. I like not having to aim the patch antenna (I have an 8dBi patch).

Also, as a point of clarification - are you guys talking about ground distance or line of sight distance? If ground distance - what height is your TX flying? I am presuming that we're all talking about Lawmate receivers here so if you have something different (and Airwave for example) please indicate accordingly.

Kilrah, I've been wondering about the LNA - does the LNA help if you're just using the whip? Or the 8dBi?

Thanks.

Daniel

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A member of our forum has gone 4km with lawmate 500 mW, and 3dbi whips on both sides. But he says not always can go this far but oftenly reaches 3 km without any problem :o . Some other members has been with him and has verified his long distance flights.

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Wow, that's encouraging! 3km is actually about as far as I want to go. Question now is if my JR 72MHz synthesized TX module with the R770S synthesized RX will go 3km. Thanks Wavess - that's exactly the info I'm looking for.

Daniel

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I am quoting Airwave 508, with a LNA I can almost double the range. Remember your range will be effected by local broadband interference so 3km may not be possable close to a built up aera.

Terry

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Wow, that's encouraging! 3km is actually about as far as I want to go. Question now is if my JR 72MHz synthesized TX module with the R770S synthesized RX will go 3km. Thanks Wavess - that's exactly the info I'm looking for.

Daniel

Well take this with a lot of care. I have tried the same config with much poorer results. I hardly get 800m-1 km. My components are placed worst than him, he has much more separation between them, and much other things that affects rf. The theorical range for that combination is about 5 km if I remember well.

Terry could you link some LNA, I suposse you guys use them on the receiver´s hand.

Edited by Wavess

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I'm also looking into a LNA for the receiver. The kit you linked to has some very nice specs - 0.3dB NF, that's really impressive. I've used a MAR-6 in the past and don't recall such good performance. It must be due to the high biased HEMT. Unfortunately, I don't think I can make that PCB so I'll have to source for something ready made. I am also concerned that at 17.5dB gain, the 3rd order IMD rejection won't be too good - maybe below 30dBm.

If any of you know of a good performing LNA, with a NF of less than 1.5dB and a gain of 14dB or more with good 3rd order IMD behaviour, please post the link here.

Daniel

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I would have expected better with the 8dBi patch though if you 500m with an omni.

I was quoting this as it was the maximum I had actually tested and proved (R/C limitations then came into play) until yesterday, hehe :P

I got about 1500m ground distance at 550m height, with a very decent picture but some short drops when the antenna was obstructed a bit more by the plane.

But theoretically a 8dBi vs 3dBi is only 5dB gain, so less than doubling the range. I have never fully tested the whip either, maybe I can get a bit more.

But what is interesting is that I compared once more my 10mW TX and a 200mW Lawmate, with the same RX setup (antenna, receiver), placed at the same location. The 200mW TX was installed in the plane's tail, at ~80cm from the RX, and about 20cm from the closest part of the RX antenna. I was limited at 800m because of R/C glitches, and I had a very noisy picture there. I then switched back to the 10mW, and flew out to those 1500m with no glitch at all, a perfect picture at 800m, and less noise at 1500m than with the 200mW at 800m.

Guess what I'll use most now (as before). I had already done a test with same result but with the 200mW at 5cm from the RX with 600m of R/C range, so this was to be a confrmation, using a different TX unit to rule out possible bad performance of the one I had used the first time.

Kilrah, I've been wondering about the LNA - does the LNA help if you're just using the whip? Or the 8dBi?

The LNA is integrated right on the antenna's PCB (where it should be) so I can't use it with other ones unfortunately.

I however found one from a link on RCGroups the other day, ordered one to test, but it's pretty pricy so if it's not a big advantage it won't be worth it. I'll report when it arrives.

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Kilrah, you show again that it's good to use minimum video TX power, I 100% agree. If it was not for broadband noise I would always use 10mW but often now I have to use 100mW.

I'm not sure why I see such a big increase in range with an 8dBi patch over an omni, my best guess is that the omni falls far short of 3dBi.

Terry

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Hi Terry,

I've seen omni's that have similar design to what we normally use being advertised as 2dB or 2.3dB gain so you may be right that 3dB could be a little optimistic.

Daniel

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