K3 Sub Receiver Antenna

[Bill N3KKM]

The K3 manual indicates that the Sub Receiver's AUX antenna must be well-isolated from the transmit antenna to avoid activating the sub's carrier carrier-operated relay. From a practical, real world standpoint, what is "well isolated?"

Bill - N3KKM
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[David Cutter]

My arrangement has them within a few feet, so I will be using a high speed
reed to remove and short the rx antenna.

David
G3UNA


----- Original Message -----
From: "Bill N3KKM" <[hidden email]>
To: <[hidden email]>
Sent: Monday, September 27, 2010 5:59 PM
Subject: [Elecraft] K3 Sub Receiver Antenna

> The K3 manual indicates that the Sub Receiver's AUX antenna must be
> well-isolated from the transmit antenna to avoid activating the sub's
> carrier carrier-operated relay. From a practical, real world standpoint,
> what is "well isolated?"
>
> Bill - N3KKM
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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[Don Wilhelm-4]

  Bill,

My answer is not a "smart remark", but rather the truth - and that
answer is "Whatever it takes!"
There are so many variables that your question cannot be answered
specifically for your location.
Some of the variables are antenna polarization, physical distance, gain
of the transmit antenna and its heading relative to the receive
antenna.  Trees, buildings and other objects that may shield the receive
antenna from the transmit ant, proximity of feedlines, how much
radiation is coming back on the feedline for each antenna, plus probably
a host of other factors that I may not have thought of.

You could make some tests using a simple pickup antenna and a field
strength meter at your proposed location for the receiving antenna
before placing it.  Position the temporary pickup antenna for the least
field strength.
Unless you have a lot of freedom in the physical location of the receive
antenna, the simple solution may be to switch in an attenuator for the
subRX when transmitting.  If the main and the sub are going to be on
different bands, perhaps a bandpass filter would be a good solution -
again, the real answer is "Whatever it takes", and hopefully you can
begin to understand why that is the only answer possible.

73,
Don W3FPR

On 9/27/2010 12:59 PM, Bill N3KKM wrote:
> The K3 manual indicates that the Sub Receiver's AUX antenna must be well-isolated from the transmit antenna to avoid activating the sub's carrier carrier-operated relay. From a practical, real world standpoint, what is "well isolated?"
>
> Bill - N3KKM
>
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[Julius Fazekas n2wn]

Bill,

Just an operating example, I have a short (well had) 330' beverage within 20 feet of my TX antenna for 160m. I have never had an issue with the relay tripping. I run LP or QRP, it may be an issue running HP, but I haven't heard any complaints from any of my friends on the Top Band.

I don't use a relay like David does, but probably will in the future to detune my TX antenna. Not because of the second RX relay, but to minimize RX antenna pattern distortion.

Probably the best thing is to use isolation transformers and current chokes, if in doubt or just to be safe. Those are relatively easy to implement. David's option is a bit more complex, but may be necessary in certain circumstances.

The easiest thing to do is try it with your current setup, if it doesn't trip, then most likely you're well enough isolated for that particular issue.

73,
Julius
n2wn

[gm3sek]

Bill N3KKM wrote:
>The K3 manual indicates that the Sub Receiver's AUX antenna must be
>well-isolated from the transmit antenna to avoid activating the sub's
>carrier carrier-operated relay. From a practical, real world
>standpoint, what is "well isolated?"
>

The easiest way to make sure is to check the RF power level from the aux
antenna using a simple "expendable" diode detector, before connecting
the antenna to the K3.

The detector can be made in a couple of minutes from a 47 ohm resistor,
a 1N4148 or similar diode and a 0.01uF ceramic capacitor. The rectified
DC output is connected to a DMM,

Any DC reading below about 1.0V will be fine.

N4ZR has also published a passive protection circuit at:

http://wiki.contesting.com/index.php/Basic_Receiver_Protection


Next time I have the covers off the K3, I plan to install at least one
+12V DC output with TX/RX switching, for use with preamps and protection
relays.


--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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[Ken Kopp-3]

If you don't want to build a protection circuit, Array
Solutions ... and others ... sell an ICE Model 196
"RF Limiter / Arrestor" that does the job nicely.  

I have several in use.

73! Ken Kopp - K0PP
       [hidden email]



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[Brett Howard]

I'm not so sure that a BPF would solve the problem even if they are on
different bands as the COR may still trip even though the subRX is on
another band...

~Brett (N7MG)

On Mon, Sep 27, 2010 at 11:38 AM, Don Wilhelm <[hidden email]> wrote:

>  Bill,
>
> My answer is not a "smart remark", but rather the truth - and that
> answer is "Whatever it takes!"
> There are so many variables that your question cannot be answered
> specifically for your location.
> Some of the variables are antenna polarization, physical distance, gain
> of the transmit antenna and its heading relative to the receive
> antenna.  Trees, buildings and other objects that may shield the receive
> antenna from the transmit ant, proximity of feedlines, how much
> radiation is coming back on the feedline for each antenna, plus probably
> a host of other factors that I may not have thought of.
>
> You could make some tests using a simple pickup antenna and a field
> strength meter at your proposed location for the receiving antenna
> before placing it.  Position the temporary pickup antenna for the least
> field strength.
> Unless you have a lot of freedom in the physical location of the receive
> antenna, the simple solution may be to switch in an attenuator for the
> subRX when transmitting.  If the main and the sub are going to be on
> different bands, perhaps a bandpass filter would be a good solution -
> again, the real answer is "Whatever it takes", and hopefully you can
> begin to understand why that is the only answer possible.
>
> 73,
> Don W3FPR
>
> On 9/27/2010 12:59 PM, Bill N3KKM wrote:
>> The K3 manual indicates that the Sub Receiver's AUX antenna must be well-isolated from the transmit antenna to avoid activating the sub's carrier carrier-operated relay. From a practical, real world standpoint, what is "well isolated?"
>>
>> Bill - N3KKM
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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