Alright so, I've been looking at lightening protection a lot lately, because really who wants that into their shack when bleeding that off and sending it to ground is a better choice. It's important to know that nothing you put in your coax is going to protect anything if a bolt of lightening smashes into your tower or your 43 foot vertical. But that is not really what lightening surge protectors do anyway. It's important to understand that all they do is take the static build up on the coax and what is being picked up by your antenna from being delivered in a huge snap down to your rig(s). It's slightly more complex than that but that is essentially what it does. There are multiple designs, in fact the one I'm going to share has could be altered even. But in short, surge protectors merely shunt high voltage to ground, keeping it out of your rig. The main item responsible for this is a "Gas Discharge Tube". If you want to read all about them you can go over to DigiKey and do so. http://www.digikey.com/Web Export/S...stPrinciplesGasDischargeTube.pdf?redirected=1
Before I continue... I'm not sure of the legalities with respect to designing your own home made lightening surge protector. I have no ideas what any insurance company would do or say if your house burns to the ground because you made your own lightening protection. If you make your own I'm not responsible, it's not my fault if your entire house burns to the ground and the insurance won't pay for it. Nor is anyone on this forum, or the owners of this forum. This is an educational thing, and hams have been building their own surge and lightening protection since the very start of ham radio, I just wanted to get the disclaimers out of the way.
Construction of your own home made system can cost as little as $15-20 with a metal case, in terms of items needed this is a relatively inexpensive build. I was only inspired to do it because I knew basically what is inside of these Polyphaser and Alpha Delta products (though NOT exactly, I've never reverse engineered either product). But the principals are basically the same as any other form of surge protection (except we're not going to use MOVs, never use a MOV in RF).
This is what your lightening surge protector looks like on the inside (more or less):
I guessed at the ceramic disc cap capacitance value, but for full legal limit you'd want a 3Kv or so cap in there. You can also add to this a resistor, say a 2-5 watts to ground (I'm not sure of value, I'm guessing you'd want it fairly high to not effect SWR, but I may be wrong) which would bleed static build up to ground constantly. The cap won't allow you to pass DC back to the input so you need to put your resistor (if used) and the GDT on the antenna side of the device. Also I want to point out that the GDT I used is (as far as I can tell) the same thing Alpha Delta uses in theirs and charges an arm and a leg for it costs $2.90 (or so) at http://www.alliedelec.com/ here's the direct link http://www.alliedelec.com/search/productdetail.aspx?SKU=70184211
Hope this helps..
Before I continue... I'm not sure of the legalities with respect to designing your own home made lightening surge protector. I have no ideas what any insurance company would do or say if your house burns to the ground because you made your own lightening protection. If you make your own I'm not responsible, it's not my fault if your entire house burns to the ground and the insurance won't pay for it. Nor is anyone on this forum, or the owners of this forum. This is an educational thing, and hams have been building their own surge and lightening protection since the very start of ham radio, I just wanted to get the disclaimers out of the way.
Construction of your own home made system can cost as little as $15-20 with a metal case, in terms of items needed this is a relatively inexpensive build. I was only inspired to do it because I knew basically what is inside of these Polyphaser and Alpha Delta products (though NOT exactly, I've never reverse engineered either product). But the principals are basically the same as any other form of surge protection (except we're not going to use MOVs, never use a MOV in RF).
This is what your lightening surge protector looks like on the inside (more or less):
I guessed at the ceramic disc cap capacitance value, but for full legal limit you'd want a 3Kv or so cap in there. You can also add to this a resistor, say a 2-5 watts to ground (I'm not sure of value, I'm guessing you'd want it fairly high to not effect SWR, but I may be wrong) which would bleed static build up to ground constantly. The cap won't allow you to pass DC back to the input so you need to put your resistor (if used) and the GDT on the antenna side of the device. Also I want to point out that the GDT I used is (as far as I can tell) the same thing Alpha Delta uses in theirs and charges an arm and a leg for it costs $2.90 (or so) at http://www.alliedelec.com/ here's the direct link http://www.alliedelec.com/search/productdetail.aspx?SKU=70184211
Hope this helps..
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