Re: ARLA/CLUSTER: Antenas de Emergência

[Luis Valadas]

Boas noite a todos
Em primeiro lugar queria explicar o porquê de ter utilizado este email para
dirigir-me a todos
Bom , eu queria perguntar se alguem tem e que possa dispensar :
- toroide 140-43
-toroide T200-2
- toroide T200-6
- alguns metros de fio de 1mm esmaltado
Devem estar a pensar que vou fazer um balum pelo menos de 9:1, de facto tem
razao, queria fazer umas antemas , e sei que existe a venda baluns ja
feitos mas confesso que gostava de eu os fazer, quanto a comprar no ebay ou
no estrangeiro tenho alguma dificuldade em faze-lo por isso peço a alguem
que tenha e que possa dispensar, claro pagando o justo valor do mesmo
material e os devidos portes
73
CT1DTE
Luis Valadas



2013/7/18 João Costa > CT1FBF <ct1fbf  gmail.com>

> More on HF – SSB - Antennas
>  Carrying on from my previous blog on engineers antennas HF and SSB<http://www.expeditioncoppelia.com/2010/10/engineers-antennas-hf-ssb.html>,
> in this second part I will more fully describe our emergency antenna setup.
>
> I draw your attention to a very useful set of resources available free on
> the internet:
> Field Antenna Handbook - US Marine Corps<http://frrl.files.wordpress.com/2009/02/usmc-antenna-hb.pdf>
>
> Radio Operators Handbook - US Marine Corps<http://hilltoparmyradios.com/usmc-radio-ops-hdbk.pdf>
>
> In the previous post I worked out the length of antenna for a given
> frequency that would provide the best chance of effective communication.
> This certainly does not mean for a given frequency if the length is
> different you can not communicate, it just means that there is more chance
> at the lengths specified.
> So how is it all going to work on the boat.
> **
> *Situation one – the antenna is broken, but the tuner is intact. *
> Cut a new antenna from a piece of wire of a length greater than 7m as
> specified for our ICOM tuner.
>
> One end of the antenna would need to be lifted towards the sky, if the
> mast or part of it is still standing the wire could be hoisted on it,
> otherwise some other pole, like the prod, kite pole or boom could be used.
> The resulting antenna would have the characteristics of this sloping wire
> antenna show below:
>
> [image: sloping wire]<http://lh6.ggpht.com/_rK1oaS0yOa8/TNNujQUNbNI/AAAAAAAAFTc/kuMS4ZHLEUg/s1600-h/sloping%20wire%5B2%5D.png>
> Sloping Wire – source: US Marine Corps (1991) “*Field Antenna Handbook*”
> pg 4-34
> *Situation two – the antenna is broken, the tuner is broken*
>
>
>
> This is the situation where  having the antenna length appropriate for the
> frequency you want to transmit of is important. Normally the tuner, tunes
> between length suitable for the frequency and the actual antenna length
> using a series of capacitors and inductors. Without a tuner each time you
> change frequency, to optimise the chance of being able to communicate the
> length of the antenna must be changed.
>
> The length of antennas required for international emergency frequency
> range between 32.6m for 2182 Hz to 11.6m for 6125Hz.
>
> 32.6m is greater than distance between the back of Coppelia and the mast
> head. Therefore the sloping wire arrangement used above can not be used.
> Moreover, it is likely that if we have broken the tuner, we might have
> suffered damage to the mast, and therefore we would not even be able to
> make a 11.6m sloping antenna.
>
> The answer is a different sort of antenna, a vertical half rhombic
> antenna.
> [image: Slide2]<http://lh6.ggpht.com/_rK1oaS0yOa8/TNNumH0uAaI/AAAAAAAAFTk/r08mwsGQ8lI/s1600-h/Slide2%5B1%5D.png>
> Vertical half rhombic antenna – source: US Marine Corps (1991) “*Field
> Antenna Handbook*” pg 4-37
>
> The plan onboard would be to make some sort of pole in the middle of the
> boat. A shielded cable would then be run from the radio to the back of the
> boat, and a second wire from the ground plate to the same location. A
> piece  of wire equal to the length of antenna required for the frequency to
> be used would then be attached to these wires, and hoisted aloft in the
> middle, then fastened at the bow. The resulting antenna setup would form a
> vertical half rhombic antenna.
>
>   *Emergency Antennas for VHF and UHF Use*
>
>     Get a piece of RG-58 coax and using the chart below, strip the outer
> jacket of the coax to that appropriate length, depending on the band you
> choose to work.  Once the outer covering has been stripped, carefully open
> the copper braid near the bottom of where you stripped the outer jacket.
> Once the braid is open, carefully bend the center conductor over and pull
> it out of the hole you opened in the copper braid.  Once you have the
> center conductor pulled free, straighten it and either form a loop at the
> top end for hanging, or solder on a terminal lug.  Remember, the antenna
> length is measured from the very end of the look or terminal lug, and they
> do add length to your antenna.  Trim as necessary.
>
>
>
>  *MHz*
>  *Length in Inches*
>  *Length in Metric*
>  52
>  54"
>  137.2 cm
>  146
>  19.2
>  48.8 cm
>  223
>  12.5"
>  31.8 cm
>  445
>  6.3"
>  16cm
>
>
>
> Fontes:  Expedition Coppelia e WCERC *VHF UHF Emergency Antennas*
>
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