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Re: Antw.: [vt-dev] Re: reading and setting the transmission rate


Carlos Rey-Moreno Jul 30, 2012 11:28 PM
Posted in group: Village Telco Development Community
I forgot to attach a picture from the inner parts of the antenna in case
helps the discussion.

Best,

Carlos

On 07/31/2012 08:14 AM, Carlos Rey-Moreno wrote:
> Hi Elektra,
>
> Thank you very much for your answer.
>
>> The added weather proofing will change the properties of the antenna
>> somehow, because the dielectric constant of the additional material
>> around it is different than free air. You can make a simple test to
>> figure that out - compare the stock antenna with a weatherproofed
>> one. I suppose it will not make much difference, if any.
> We did the tests (including the braid not touching anything in the RF
> circuit), and the differences are not even perceptible with the tools
> we have at hand (horst.sh, wlanconfig).
>>> For c), we're going to run some tests the weekend for checking with
>>> some
>>> spare antennas and pigtails we have if we obtain the 9 dBis before
>>> waterproofing them. If not, I'm thinking on using the reflector you
>>> designed. Do you think it behaves like a 180º sectoral antenna? or is
>>> more a directional one on the 45º angle that you mentioned?
>> The gain of the external reflector is nowhere close to the claimed
>> 9dBi. Rather 3-5dBi. But I'd love to get some feedback on the reflector.
> For us considering using the reflector I would like to know what is
> the sector you're expecting to obtain. because if it is very narrow
> then I don't think it will make a difference with the antennas we have
> (see below).
>>
>> Here is a interesting web page discussing the gain of collinear
>> dipoles. In order to achive 9dbi / 7 dBd, a collinear dipole antenna
>> requires 6 collinear dipoles of at least 0.1λ end-to-end spacing:
>>
>> http://www.w8ji.com/stacking_broadside_collinear.htm
>>
>> In order to provide that gain, the elements and the distance between
>> elements alone adds up to a length of at least ~ 41cm for the
>> antenna, without antenna socket. How long is the omni that you are
>> using? How many elements are inside?
> The antenna we have is 39 cm long however it counts only with three
> λ/4 elements and the maximum-current spacing is 0.64λ in between two
> of the them and 0.7λ in between the other two. According to the
> graphics on the web page you sent us that should give us in between 4
> and 5 dBi gain. In the test we found this difference or even bigger,
> however is not at all omnidirectional and that gain is obtained in a
> very narrow beam.
>
> So, we're going to do our best with the tools we have (the network is
> feasible still), although it seems clear that additional investments
> in proper external antennas are needed to obtain the RSSI I was aiming
> with these ones.
>
> Best,
>
> Carlos