Topband: Detuning TX ant + QSK

[John Kaufmann]

The user's manual I wrote for the YCCC low-band receiving array contains a section on detuning antennas that are near the receiving array.  You can download the manual at:  https://static.dxengineering.com/global/images/instructions/dxe-yccc-switch.pdf.  (If the URL wraps because this text gets reformatted, be sure to copy the entire address).   See pages 46-48 of the manual.  Figure 39 on p. 47 shows a simple circuit that I use with my K3 for simultaneously keying my amplifier (AL-1200 with the QSK-5 option) and the vacuum relays (via a driver transistor) on my TX verticals.  The same circuit should work with other radios and amplifiers.  I used a simple 1N4001 back EMF diode in this circuit.  I'm not sure whether a "faster" diode would be better but this seems to work for me.  

The most important thing is to prevent hot-switching the vacuum relays by applying RF before the contacts close fully.  On my K3, I set the QSK delay to 10 ms and I get excellent QSK operation with this setup.  The vacuum relays have held up just fine over 5 or 6 years of operation so I don't think hot-switching has been an issue.  

73, John W1FV


-----Original Message----- 
From: Richard (Rick) Karlquist
Sent: Wednesday, November 28, 2018 7:02 AM
To: jkaufmann at alum.mit.edu ; 'Jim Thomson' ; 'TopBand List'
Subject: Re: Topband: Detuning TX ant + QSK



On 11/28/2018 5:18 AM, John Kaufmann wrote:
> Jim,
>
> I use Gigavac GH-1 vacuum relays for detuning my TX antennas when 
> receiving.  The contact closure/release time is 6 msec.  You have to dial 
> in enough QSK delay in your radio so that you don't hot-switch the relays.
>
> 73, John W1FV
>

A quick note on the GH-1:

1.  In theory, there is no limit to speeding up closure.
OTOH, release can only be speeded up to the extent of collapsing
the magnetic field by omitting the usual reverse voltage
protection diode.  After that, the mechanical response
remains.

2.  This works neatly with the GH-1 being energized on
transmit, where you want the quickest response.

3.  The limiting factor to speeding up this model is
contact bounce.  You can only apply a modest amount
of speed up before you are limited by contact bounce.
With other models, of course, YMMV.

73
Rick N6RK 

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