From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: Re[2]: LF: Re: Antenna relays
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Date: Thu, 19 Nov 2015 20:24:54 +0000
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Subject: RE: Re[2]: LF: Re: Antenna relays
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Status: O

Hi Chris,

your question is not easy at all, unless you want to spend  a lot of money.
The easy (but expensive) solution would be to buy an appropiate vacuum relay. These can handle several 10kV and are RF-proof.
As mentioned before for most other (and affordable) relays the contact voltages are given for DC or 50 (60) Hz. RF behaviour (even as low as 136kHz) will be different (worse). And RF voltages of several kV are very common on 136kHz.
One option would be to put a number of relays "in series", but there are some pitfalls:
- it will increase the (open) contact voltage, but not the contact-to-coil voltage (unless you will provide some kind of isolation in the relay driver)
- you have to ensure that the voltage is equally divided over the relays: at least use identical relays, eventually equal (high voltage) resistors in parallel with each contact.

Marcus offered an interesting alternative, but the bifilar loading coil would need to have a low DC resistance (thus heavy wire).

73, Rik  ON7YD


________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Chris Wilson [chris@chriswilson.tv]
Verzonden: donderdag 19 november 2015 20:40
Aan: Rik Strobbe
Onderwerp: Re[2]: LF: Re: Antenna relays

Hello Rik,

Thursday, November 19, 2015


Whilst you experts argue the technical niceties of the challenge, let
me ask what might be a simple question to you guys. What is the
minimum number of two contact vac relays I would need to go from
strapped ladder line to top of loading coil, to unstrapped ladder
line, disconnected from the top of the coil, and now connected to my
coaxial feed line, presumably itself disconnected from ground and the
bottom of the loading coil? It seems a lot would be needed to me....
:( Thanks! I can see me leaving wet weather gear by the front door and
doing this manually!


> Hello Stefan,

> I am not sure a (lossless) capacitor in parallel with the coil will lower the antenna efficiency.
> I would assume that it will affect the antenna impedance as seen
> from the TX, but will not change the ratio Rrad/Rloss (what
> determines the antenna effeciency).

> 73, Rik  ON7YD


--
Best regards,
 Chris  2E0ILY                          mailto:chris@chriswilson.tv