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Diversity receive and isolating antennas

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George Thornton

Diversity receive and isolating antennas

I am planning to use my dual receive K3 for field day and we want to try
out diversity receive.

This particular setup will be for 20 meters only. The primary antenna
will be a 20 meter monoband Yagi mounted on a 40-60 ft. tower.

We were considering using a Buddipole mounted in vertical position and
tuned for 20 meters voice to serve as a Rx only antenna for the sub.
All transmission will be from the Yagi. I was planning to hook the
Buddipole into a Rx only connector.

We will do the best we can to isolate the two antennas but having not
been to the site before I am not sure what will be possible in the way
of geographic isolation.

I want to make sure I won't do any damage to the K3 in case the
isolation is not sufficient.

Anyone familiar with this situation able to give me some guidance?

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wayne burdick

Re: Diversity receive and isolating antennas

Administrator

Hi George,

If you have an RF voltmeter or milliwatt meter, try terminating the
proposed RX antenna in a dummy load, then measure the voltage or power
when you transmit. If it's less than about 2.23 Vrms (100 mW, or +20
dBm), you'll have no trouble at all.

The subreceiver (as well as the RX ANT IN jack) can generally handle
far more than this without damage; I pumped several watts in during
early testing. But you don't want to take risks in the field, or have
the COR (carrier operated relay) switching in and out during keying in
CW mode. Antennas can change pattern due to wind, rotation, etc.

If the power at the AUX RX input (sub receiver) looks like it may be
excessive, you can take additional precautions. You could move the RX
antenna farther away, put it in a null of the TX antenna, reduce its
gain (length), or use the KEY OUT line to drive an external shunt PIN
diode switch.

73,
Wayne
N6KR

On Jun 24, 2010, at 10:04 AM, George A. Thornton wrote:

> I am planning to use my dual receive K3 for field day and we want to
> try
> out diversity receive.
>
>
>
> This particular setup will be for 20 meters only. The primary antenna
> will be a 20 meter monoband Yagi mounted on a 40-60 ft. tower.
>
>
>
> We were considering using a Buddipole mounted in vertical position and
> tuned for 20 meters voice to serve as a Rx only antenna for the sub.
> All transmission will be from the Yagi. I was planning to hook the
> Buddipole into a Rx only connector.
>
>
>
> We will do the best we can to isolate the two antennas but having not
> been to the site before I am not sure what will be possible in the way
> of geographic isolation.
>
>
>
> I want to make sure I won't do any damage to the K3 in case the
> isolation is not sufficient.
>
>
>
> Anyone familiar with this situation able to give me some guidance?
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> 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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Jim Brown-10

Re: Diversity receive and isolating antennas

In reply to this post by George Thornton

On Thu, 24 Jun 2010 10:04:28 -0700, George A. Thornton wrote:

>Anyone familiar with this situation able to give me some guidance?

In addition to the the good comments you've received about isolation
based on antenna orientation and location, consider using a simple
passive attenutator on the RX antenna input if you hear the COR
clicking. Especially on the lower HF bands, noise received on the
antenna is much greater than noise internal to the K3, so you can
often use 10-20dB of attenuation without degrading signal to noise
ratio.

I mostly use Beverages to feed my 2nd RX. I'm using the very
excellent DX Eng preamp, and on some band/antenna combinations I
need an attenuator between the preamp and the rig to prevent the COR
from operating.

You can sometimes find precision attenuators at hamfests, and you
can build your own non-precision attenuator with a few resistors.
Impedance matching is not a big deal -- anything that is in the
ballpark will work fine. It goes in line between the RX antenna and
the RX antenna input.

To roll your own for 10 dB, use something like 82 ohms across the
antenna, 68 ohms in series, and 47 ohms across the RX antenna input.
For 20dB, use something like 56 or 68 ohms across the RX antenna,
470 ohms in series, and 47 ohms across the RX antenna input.
Resistor values are not critical, but keep leads short and don't use
wire wound resistors. :)

73, Jim Brown K9YC

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Brett Howard

Re: Diversity receive and isolating antennas

In reply to this post by wayne burdick

This just gave me a great idea... If any of you have a LP-100A you
can connect an antenna directly into the back of the unit (where the
couplers normally connect) and the unit can then be used as a field
strength meter and it will give values in dBm... Thats totally how
I'm going to determine if my separation is going to be good enough...

My hope is to be able to have 3 antennas on the K3 two which are TX/RX
and one RX only... The RX only antenna I'm going to run through an
ICE 196 RF Limiter
(http://www.iceradioproducts.com/reconly.html#rflimiter). It starts
limiting things to .3VRms so that should keep things happy...

~Brett (N7MG)

On Thu, Jun 24, 2010 at 11:14 AM, Wayne Burdick <[hidden email]> wrote:

> Hi George,
>
> If you have an RF voltmeter or milliwatt meter, try terminating the
> proposed RX antenna in a dummy load, then measure the voltage or power
> when you transmit. If it's less than about 2.23 Vrms (100 mW, or +20
> dBm), you'll have no trouble at all.
>
> The subreceiver (as well as the RX ANT IN jack) can generally handle
> far more than this without damage; I pumped several watts in during
> early testing. But you don't want to take risks in the field, or have
> the COR (carrier operated relay) switching in and out during keying in
> CW mode. Antennas can change pattern due to wind, rotation, etc.
>
> If the power at the AUX RX input (sub receiver) looks like it may be
> excessive, you can take additional precautions. You could move the RX
> antenna farther away, put it in a null of the TX antenna, reduce its
> gain (length), or use the KEY OUT line to drive an external shunt PIN
> diode switch.
>
> 73,
> Wayne
> N6KR
>
>
> On Jun 24, 2010, at 10:04 AM, George A. Thornton wrote:
>
>> I am planning to use my dual receive K3 for field day and we want to
>> try
>> out diversity receive.
>>
>>
>>
>> This particular setup will be for 20 meters only. The primary antenna
>> will be a 20 meter monoband Yagi mounted on a 40-60 ft. tower.
>>
>>
>>
>> We were considering using a Buddipole mounted in vertical position and
>> tuned for 20 meters voice to serve as a Rx only antenna for the sub.
>> All transmission will be from the Yagi. I was planning to hook the
>> Buddipole into a Rx only connector.
>>
>>
>>
>> We will do the best we can to isolate the two antennas but having not
>> been to the site before I am not sure what will be possible in the way
>> of geographic isolation.
>>
>>
>>
>> I want to make sure I won't do any damage to the K3 in case the
>> isolation is not sufficient.
>>
>>
>>
>> Anyone familiar with this situation able to give me some guidance?
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Stewart Baker

Re: Diversity receive and isolating antennas

Used my LP-100A to check the isolation between my main antennas and pennant
receive loops, worked out great.

Stewart G3RXQ
On Thu, 24 Jun 2010 11:27:52 -0700, Brett Howard wrote:

> This just gave me a great idea... If any of you have a LP-100A you
> can connect an antenna directly into the back of the unit (where the
> couplers normally connect) and the unit can then be used as a field
> strength meter and it will give values in dBm... Thats totally how
> I'm going to determine if my separation is going to be good enough...
>
> My hope is to be able to have 3 antennas on the K3 two which are TX/RX
> and one RX only... The RX only antenna I'm going to run through an
> ICE 196 RF Limiter
> (http://www.iceradioproducts.com/reconly.html#rflimiter). It starts
> limiting things to .3VRms so that should keep things happy...
>
> ~Brett (N7MG)
>
> On Thu, Jun 24, 2010 at 11:14 AM, Wayne Burdick <[hidden email]> wrote:
>> Hi George,
>>
>> If you have an RF voltmeter or milliwatt meter, try terminating the
>> proposed RX antenna in a dummy load, then measure the voltage or power
>> when you transmit. If it's less than about 2.23 Vrms (100 mW, or +20
>> dBm), you'll have no trouble at all.
>>
>> The subreceiver (as well as the RX ANT IN jack) can generally handle
>> far more than this without damage; I pumped several watts in during
>> early testing. But you don't want to take risks in the field, or have
>> the COR (carrier operated relay) switching in and out during keying in
>> CW mode. Antennas can change pattern due to wind, rotation, etc.
>>
>> If the power at the AUX RX input (sub receiver) looks like it may be
>> excessive, you can take additional precautions. You could move the RX
>> antenna farther away, put it in a null of the TX antenna, reduce its
>> gain (length), or use the KEY OUT line to drive an external shunt PIN
>> diode switch.
>>
>> 73,
>> Wayne
>> N6KR
>>
>>
>> On Jun 24, 2010, at 10:04 AM, George A. Thornton wrote:
>>
>>> I am planning to use my dual receive K3 for field day and we want to
>>> try
>>> out diversity receive.
>>>
>>>
>>> This particular setup will be for 20 meters only. The primary antenna
>>> will be a 20 meter monoband Yagi mounted on a 40-60 ft. tower.
>>>
>>>
>>> We were considering using a Buddipole mounted in vertical position and
>>> tuned for 20 meters voice to serve as a Rx only antenna for the sub.
>>> All transmission will be from the Yagi. I was planning to hook the
>>> Buddipole into a Rx only connector.
>>>
>>>
>>> We will do the best we can to isolate the two antennas but having not
>>> been to the site before I am not sure what will be possible in the way
>>> of geographic isolation.
>>>
>>>
>>> I want to make sure I won't do any damage to the K3 in case the
>>> isolation is not sufficient.
>>>
>>>
>>> Anyone familiar with this situation able to give me some guidance?
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html