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Diversity receive with ant1 and ant2?

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tomb18

Diversity receive with ant1 and ant2?

Hi,
I have a question about the diversity mode where you use ant1 on the main receiver and ant2 on the sub. IN the manual it says "This requires that the two antennas connected to the KAT3 be well isolated from each other. If not, the sub receiver’s carrier-operated relay may turn on during transmit."

How does one know that this is the case? I am currently using this and it seems to operate as always.
My antenna 1 is a dipole in the attic and antenna 2 is a vertical separated about 30 feet apart.

Thanks for any help.

Don Wilhelm-4

Re: Diversity receive with ant1 and ant2?

If you hear the COR relay clicking while transmitting, you do not have
enough isolation between the TX and RX antennas (or your power is
greater than the isolation of the antennas will permit).

73,
Don W3FPR

On 10/7/2011 11:31 PM, tomb18 wrote:

> Hi,
> I have a question about the diversity mode where you use ant1 on the main
> receiver and ant2 on the sub. IN the manual it says "This requires that the
> two antennas connected to the KAT3 be well isolated from each other. If not,
> the sub receiver’s carrier-operated relay may turn on during transmit."
>
> How does one know that this is the case? I am currently using this and it
> seems to operate as always.
> My antenna 1 is a dipole in the attic and antenna 2 is a vertical separated
> about 30 feet apart.

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tomb18

Re: Diversity receive with ant1 and ant2?

Is the noise loud?
What if COR actually engages? Will this damage something?

Thanks

Don Wilhelm-4

Re: Diversity receive with ant1 and ant2?

A COR (Carrier Operated Relay) is a protective device. It shunts the
receiver input to ground if it detects a signal large enough to
potentially cause damage.

Yes, you should not rely on the COR to protect the receiver. If you
hear it clicking, either reduce the power or move the RX antenna further
away from the field of the TX antenna.

73,
Don W3FPR

On 10/9/2011 1:17 AM, tomb18 wrote:
> What if COR actually engages? Will this damage something?
>
>
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tomb18

Re: Diversity receive with ant1 and ant2?

Ok, so the click should be audible? Is it like the other clicks i.e. the antenna tuner? Wouldn't a good option be to turn off the sub while transmitting during diversity mode? Could this be done in firmware?
I'm really liking the diversity mode for the faint dx.

Don Wilhelm-4

Re: Diversity receive with ant1 and ant2?

I don't think turning off the sub will do the job - the antenna is still
connected to the receiver input.
There are devices available to remove the antenna during transmit, but I
would tend to make up my own. A relay that is activated by the K3 KEY
OUT line would be quite able to do that task.

The relay does not have to be very large since it only handles the RX
antenna. The relay contacts simply open the path between the K3 antenna
input and the RX antenna, and closes that path for non-transmit.

73,
Don W3FPR

On 10/9/2011 2:04 PM, tomb18 wrote:

> Ok, so the click should be audible? Is it like the other clicks i.e. the
> antenna tuner? Wouldn't a good option be to turn off the sub while
> transmitting during diversity mode? Could this be done in firmware?
> I'm really liking the diversity mode for the faint dx.
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Diversity-receive-with-ant1-and-ant2-tp6871758p6874855.html
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tomb18

Re: Diversity receive with ant1 and ant2?

Ok that's a good idea but it raises another question!
What about just having two antennas connected to the K3 as I do, when I don't use the sub? Isn't this exactly the same thing? Wouldn't this also potentially cause a problem too? Please keep in mind I am not using the rx antenna port but rather the sub receiver is connected to the ATU. Is this not a good idea even if it is off?

Don Wilhelm-4

Re: Diversity receive with ant1 and ant2?

Turning the sub off is not going to prevent damage to it. With your
configuration, the sub AUX ANT input is connected at all times to the
non-TX antenna. Protecting the RX input is the purpose of the COR
relay, and it will do the job in most cases, although continually having
the COR activated is not a great idea either.

I am sorry that I did not think that you were using both antennas for
transmit. You only indicated that you had the RX antenna connected to
ANT2, now "the rest of the story" becomes apparent.

You could use a relay in each antenna line that is capable of handling
the 100 watt TX power. Connect it so the non-energized path connects
the two coax leads.

Now, you will have to manually steer the "activate the relay when
transmitting" to the non-TX antenna.
You could use the NO contacts to connect to two dummy loads just in case
you forget to operate the manual switch properly - the K3 TX signal will
always see a decent load.

Sure, there may be automated ways to do that task like 'read the AI data
that can be made to flow over the RS-232 signal lines', but that would
take some intelligent processing. Alternately, you could mod the KAT3
to bring out the signal that activates ANT2 for transmit - that would
take some logic too, but it is more straightforward than attempting to
read the RS-232 data.

I have not done any similar design work, I am simply throwing out ideas
about how it *could* be done.

It might just be easier to separate the antennas than to do it the
clever and automated way..

73,
Don W3FPR

On 10/9/2011 5:30 PM, tomb18 wrote:

> Ok that's a good idea but it raises another question!
> What about just having two antennas connected to the K3 as I do, when I
> don't use the sub? Isn't this exactly the same thing? Wouldn't this also
> potentially cause a problem too? Please keep in mind I am not using the rx
> antenna port but rather the sub receiver is connected to the ATU. Is this
> not a good idea even if it is off?
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Diversity-receive-with-ant1-and-ant2-tp6871758p6875240.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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tomb18

Re: Diversity receive with ant1 and ant2?

Ok this is more complicated than it seems. What was not apparent to me is that Ant 1 and Ant 2 must be isolated in anything other than diversity mode. But what happens when you are sharing the antenna? i.e. Ant 1 is used by both receivers (with the 3db loss) and you transmit on Ant 1? I presume the main receiver input is grounded. Is the sub receiver is grounded as well?

I guess I do not still grasp the overall operation of the radio when transmit occurs.

So the question is how isolated do the antennas have to be? I have two antennas, one a dipole in an attic. At the end of this dipole, outside and about 15 feet away (at right angles to the dipole) is a cushcraft vertical. I am only running 100w and so far I cannot tell if the cor has activated. I do not think so in the month or so I have been running it.

What if the power goes up to the KPA500?
Does this mean I should remove the subreceiver if the antennas are not isolated enough?

tomb18

Re: Diversity receive with ant1 and ant2?

Ok, I have more answers.
If the sub is sharing an antenna, you do not have to worry about antenna isolation, only if you are using a separate antenna for the sub. Furthermore, the RF on the receive antenna should not be higher than 2 Watts of power.
Now this opens a question; Why didn't the K3 design allow an option to automatically isolate the sub on transmit i.e. either disconnecting the antenna completely or grounding it?
This would have given the sub much greater utility. Of course this can be done with a relay and the key out but this would fix the antenna to just one since it does not seem that there is an easy way to tell which antenna is the transmit antenna externally or is there?

I would like to be able to use diversity mode with ant1 and ant2 but choose which antenna will be the transmit one as I am listening (reverse ant1 and ant2 role depending on the signal).
Is there a way to sense the rf signal in one antenna and then trip a relay to short the other antenna to ground?