Question re K3 diversity reception

[Jim Garland]

In using my K3 for diversity reception, I use my G5RV antenna on the AUX subreceiver input, and my SteppIR for the main (transmitting/receiving) antenna.  When I’m transmitting, does the K3 short the input to the subreceiver AUX input, or otherwise protect the input from damage?  I’m using an amplifier, and the G5RV probably has many volts of RF induced on it when I’m transmitting, and I don’t want to damage anything.  Sorry if this has been covered before or, worse, if the answer is in the manual.

73,

Jim W8ZR

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[wayne burdick]

Dr. James C. Garland wrote:

> In using my K3 for diversity reception, I use my G5RV antenna on the
> AUX subreceiver input, and my SteppIR for the main
> (transmitting/receiving) antenna.  When I’m transmitting, does the K3
> short the input to the subreceiver AUX input, or otherwise protect the
> input from damage?  I’m using an amplifier, and the G5RV probably has
> many volts of RF induced on it when I’m transmitting, and I don’t want
> to damage anything.  Sorry if this has been covered before or, worse,
> if the answer is in the manual.

Hi Jim,

The KRX3's AUX input is protected by a gas-discharge tube, bleeder
resistor, and carrier-operated relay. It is very unlikely to be
damaged. However, activation of the COR (which you would hear as you
key the rig, etc.) can be disruptive to T-R sequencing. If you hear the
COR relay go on, I'd strongly suggest that you either reduce the
coupling between the two antennas or provide external switching or
shorting (this could be done via the KEY OUT jack on the K3).

73,
Wayne
N6KR

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[N2TK]

Wayne,
To carry this one step more, what about when I am running multiple K3's on
different bands at the same time? Do you recommend to use external receive
bandpass filters on the receive lines if I am using receive antennas on  the
Receive Antenna and/or Aux input?
And also use transmit bandpass filters on the transmit antenna input when I
am using the transmit antenna for both receive and transmit?

73,
N2TK, Tony

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of wayne burdick
Sent: Tuesday, December 16, 2008 1:58 PM
To: Dr. James C. Garland
Cc: [hidden email]
Subject: [Elecraft] Re: Question re K3 diversity reception

Dr. James C. Garland wrote:

> In using my K3 for diversity reception, I use my G5RV antenna on the
> AUX subreceiver input, and my SteppIR for the main
> (transmitting/receiving) antenna.  When I’m transmitting, does the K3
> short the input to the subreceiver AUX input, or otherwise protect the
> input from damage?  I’m using an amplifier, and the G5RV probably has
> many volts of RF induced on it when I’m transmitting, and I don’t want
> to damage anything.  Sorry if this has been covered before or, worse,
> if the answer is in the manual.

Hi Jim,

The KRX3's AUX input is protected by a gas-discharge tube, bleeder
resistor, and carrier-operated relay. It is very unlikely to be
damaged. However, activation of the COR (which you would hear as you
key the rig, etc.) can be disruptive to T-R sequencing. If you hear the
COR relay go on, I'd strongly suggest that you either reduce the
coupling between the two antennas or provide external switching or
shorting (this could be done via the KEY OUT jack on the K3).

73,
Wayne
N6KR

---

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[wayne burdick]

Tony, N2TK wrote:

> Wayne,
> To carry this one step more, what about when I am running multiple
> K3's on
> different bands at the same time? Do you recommend to use external
> receive
> bandpass filters on the receive lines if I am using receive antennas
> on  the
> Receive Antenna and/or Aux input?
> And also use transmit bandpass filters on the transmit antenna input
> when I
> am using the transmit antenna for both receive and transmit?

Hi Tony,

Every multi-transmitter installation is different. In general, TX and
RX antennas should be well-isolated.

If you hear the COR (carrier operated relay) on any K3 activate --
either the one on its RX ANT jack or the sub receiver's AUX input --
you should try to improve isolation. You'll know it when you hear it,
because T-R normally involves only PIN diodes on a K3. There will be
extreme cases where a band-pass filter or external shorting may be
required, depending on the situation.

There are many multi-K3 installations, some permanent, some for
DXpeditions. We've had many reports about the ability of the K3 to
function well in such cases -- often much better than older rigs. I'm
sure you can get further help in specific situations from some of those
monitoring this list.

I'm not the right guy to ask, at least at present. My entire massive HF
antenna farm is a 50' random wire, 20' up, fed with 300-ohm twin lead.
I have to sign some sort of XYL-related legal papers or buy more
acreage if I want to expand :)

73,
Wayne
N6KR

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[W8ZN]

As an add-on, we have used a pair of K3's at K8GP multi multi VHF station on 6m. Our 5 element and 7 element antennas were only several hundred feet apart and we didn't hear the COR come on and we could actually copy stations 20 KHz away from our transmitter running 1500w!!!

I'm sure this sends chills down Wayne's back but it works!!!

Terry
 -------------- Original message ----------------------
From: wayne burdick <[hidden email]>

> Tony, N2TK wrote:
>
> > Wayne,
> > To carry this one step more, what about when I am running multiple
> > K3's on
> > different bands at the same time? Do you recommend to use external
> > receive
> > bandpass filters on the receive lines if I am using receive antennas
> > on  the
> > Receive Antenna and/or Aux input?
> > And also use transmit bandpass filters on the transmit antenna input
> > when I
> > am using the transmit antenna for both receive and transmit?
>
> Hi Tony,
>
> Every multi-transmitter installation is different. In general, TX and
> RX antennas should be well-isolated.
>
> If you hear the COR (carrier operated relay) on any K3 activate --
> either the one on its RX ANT jack or the sub receiver's AUX input --
> you should try to improve isolation. You'll know it when you hear it,
> because T-R normally involves only PIN diodes on a K3. There will be
> extreme cases where a band-pass filter or external shorting may be
> required, depending on the situation.
>
> There are many multi-K3 installations, some permanent, some for
> DXpeditions. We've had many reports about the ability of the K3 to
> function well in such cases -- often much better than older rigs. I'm
> sure you can get further help in specific situations from some of those
> monitoring this list.
>
> I'm not the right guy to ask, at least at present. My entire massive HF
> antenna farm is a 50' random wire, 20' up, fed with 300-ohm twin lead.
> I have to sign some sort of XYL-related legal papers or buy more
> acreage if I want to expand :)
>
> 73,
> Wayne
> N6KR
>
> ---
>
> http://www.elecraft.com
>
> _______________________________________________
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[Jerry Flanders]

Hi Wayne

At what approx. RF voltage level sent back into the rx from the
second antenna do we need to worry about additional protection like
external switching or shorting?

Also, what do I hear when the COR activates? What sound? Is this a reed relay?

I operate SO2R and occasionally need to measure to verify safe RF
level into the second rig and would also like use my 2nd K3
(synch-tuned) for diversity rx while tx'ing on 1st K3. An actual RF
voltage level I can use as a measurable limit would be a very useful
parameter.

Jerry W4UK

At 01:57 PM 12/16/2008, wayne burdick wrote:
>Dr. James C. Garland wrote:
>
>>...  When I'm transmitting, does the K3 short the input to the
>>subreceiver AUX input, or otherwise protect the input from damage? .

>Hi Jim,
>
>The KRX3's AUX input is protected by a gas-discharge tube, bleeder
>resistor, and carrier-operated relay. It is very unlikely to be
>damaged. However, activation of the COR (which you would hear as you
>key the rig, etc.) can be disruptive to T-R sequencing. If you hear
>the COR relay go on, I'd strongly suggest that you either reduce the
>coupling between the two antennas or provide external switching or
>shorting (this could be done via the KEY OUT jack on the K3).
>
>73,
>Wayne
>N6KR

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[wayne burdick]

[hidden email] wrote:

> As an add-on, we have used a pair of K3's at K8GP multi multi VHF
> station on 6m. Our 5 element and 7 element antennas were only several
> hundred feet apart and we didn't hear the COR come on and we could
> actually copy stations 20 KHz away from our transmitter running
> 1500w!!!
>
> I'm sure this sends chills down Wayne's back but it works!!!

Awesome, Terry. I'm over the chill, and now I want to hear it myself :)

Wayne
N6KR

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[wayne burdick]

Jerry Flanders wrote:

> At what approx. RF voltage level sent back into the rx from the second
> antenna do we need to worry about additional protection like external
> switching or shorting?

The short answer is: the voltage resulting from input power high enough
to trigger the COR (probably 0.5 to 2 W in most cases). This will vary
widely because the impedance of the sub's antenna on the *transmit*
band may be totally different from its Z on the sub's receive band. At
very high impedances, strays from the coax and the COR circuitry itself
come into play. If you use the KAT3's non-TX antenna as the sub's AUX
source, the small amount of leakage between ANT1 and ANT2 can also
affect the COR trigger level; this will depend on the load Z and will
vary from band to band.

> Also, what do I hear when the COR activates? What sound? Is this a
> reed relay?

You'll hear about the same thing you hear when you switch from CW to
SSB mode (this throws a relay on the KREF3 module), except it will
follow the keying. It's not a reed relay, but it is small, and rated
for very long mechanical life. Still, I recommend not pushing it. If
you hear it, you should improve the antenna isolation on that band.

> I operate SO2R and occasionally need to measure to verify safe RF
> level into the second rig and would also like use my 2nd K3
> (synch-tuned) for diversity rx while tx'ing on 1st K3. An actual RF
> voltage level I can use as a measurable limit would be a very useful
> parameter.

What I mentioned above is the best I can give you. If you can keep it
to 10 Vpp or less, I think you'll be OK, but I'd still advise testing
things before you operate in a contest.

73,
Wayne
N6KR

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[Ed Gray W0SD]

Wayne,

What about Snow static on the main antenna and danger to the rcv?  It is
fairly high voltage and I assume not much current? I had a bunch during
the 10 meter contest.  Those of us in the north country hear it snapping
in the antenna switch quite regularly if not grounded during the winter
time.  I have never had trouble with previous radios but wondered since
I have read comments about induced power from a passing thunder storm so
in these cases you should unhook the K3.

Ed W0SD



wayne burdick wrote:

> Jerry Flanders wrote:
>
>> At what approx. RF voltage level sent back into the rx from the second
>> antenna do we need to worry about additional protection like external
>> switching or shorting?
>
> The short answer is: the voltage resulting from input power high enough
> to trigger the COR (probably 0.5 to 2 W in most cases). This will vary
> widely because the impedance of the sub's antenna on the *transmit* band
> may be totally different from its Z on the sub's receive band. At very
> high impedances, strays from the coax and the COR circuitry itself come
> into play. If you use the KAT3's non-TX antenna as the sub's AUX source,
> the small amount of leakage between ANT1 and ANT2 can also affect the
> COR trigger level; this will depend on the load Z and will vary from
> band to band.
>
>> Also, what do I hear when the COR activates? What sound? Is this a
>> reed relay?
>
> You'll hear about the same thing you hear when you switch from CW to SSB
> mode (this throws a relay on the KREF3 module), except it will follow
> the keying. It's not a reed relay, but it is small, and rated for very
> long mechanical life. Still, I recommend not pushing it. If you hear it,
> you should improve the antenna isolation on that band.
>
>> I operate SO2R and occasionally need to measure to verify safe RF
>> level into the second rig and would also like use my 2nd K3
>> (synch-tuned) for diversity rx while tx'ing on 1st K3. An actual RF
>> voltage level I can use as a measurable limit would be a very useful
>> parameter.
>
> What I mentioned above is the best I can give you. If you can keep it to
> 10 Vpp or less, I think you'll be OK, but I'd still advise testing
> things before you operate in a contest.
>
> 73,
> Wayne
> N6KR
>
> ---
>
> http://www.elecraft.com
>
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[wayne burdick]

Ed Gray W0SD wrote:

> What about Snow static on the main antenna and danger to the rcv?  It
> is fairly high voltage and I assume not much current? I had a bunch
> during the 10 meter contest.  Those of us in the north country hear it
> snapping in the antenna switch quite regularly if not grounded during
> the winter time.  I have never had trouble with previous radios but
> wondered since I have read comments about induced power from a passing
> thunder storm so in these cases you should unhook the K3.

Every antenna jack in the K3 includes a static-charge bleeder resistor.
If you see DC build-up despite this, let me know and we'll think of
something else.

73,
Wayne
N6KR

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[Julius Fazekas n2wn]

Tony,

There is a bunch of info online that addresses your question. Look for W3NQN filters, notch filters, http://www.n6rk.com/loopantennas/pacificon.pdf , coax stubs, VP6DX presentations, ICE, CQ-Contest reflector.

>From what I've read and talked with others about, it's a rare situation that you would not need something even at LP levels. HP it's pretty much a given. The biggest decision you may have to make is what will work for you... Oh and how much time and/or money to put into getting it right.

One could argue that with all the RF floating around most neighborhoods, band pass filters are a definite plus for weak signal work on the low bands.

Too, check out the YCCC, and other big contest group or station, websites for ideas about what works and what does not.

73,
Julius


"Subject: RE: [Elecraft] Re: Question re K3 diversity reception

Wayne,
To carry this one step more, what about when I am running multiple K3's on
different bands at the same time? Do you recommend to use external receive
bandpass filters on the receive lines if I am using receive antennas on  the
Receive Antenna and/or Aux input?
And also use transmit bandpass filters on the transmit antenna input when I
am using the transmit antenna for both receive and transmit?"


Julius Fazekas
N2WN

Tennessee Contest Group
TnQP http://www.tnqp.org/

Elecraft K2/100 #4455
Elecraft K3/100 #366
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[Jerry Flanders]

I have been using SO2R in some of the RTTY contests for several years
now. When I first set it up I was concerned about blowing the front
end transistors in my (then) paired ICOM 756PRO radios. It occurred
to me that I could simply measure RF voltage coming back in from the
"other" antenna when under full power and verify that I was below the
voltage that might damage the input devices. I made up a simple 50
ohm loaded diode probe for the measurements with my DVM.

The usual techniques of stubs and filters, along with antenna
separation of apprx a hundred feet, yielded worst-case voltages of
around 300 mv with 1000 watts tx'ed on the "other" antenna. I assumed
this could easily be tolerated by the radios and so far this has
proven correct through 3 generations of different pairs of radios.

I would recommend this technique of actually measuring the incoming
voltage, then use common sense as to what levels are
tolerable.  Yesterday Wayne gave some guidance on tolerable levels
with the K3, removing some of the guesswork.

Jerry W4UK

>"Subject: RE: [Elecraft] Re: Question re K3 diversity reception
>
>Wayne,
>To carry this one step more, what about when I am running multiple K3's on
>different bands at the same time? Do you recommend to use external receive
>bandpass filters on the receive lines if I am using receive antennas on  the
>Receive Antenna and/or Aux input?
>And also use transmit bandpass filters on the transmit antenna input when I
>am using the transmit antenna for both receive and transmit?"
>
>
>Julius Fazekas
>N2WN
>
>Tennessee Contest Group

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[Jay Bromley]

http://www.pvrc.org/~n4zr/Articles/simple_protection_for_the_fledgl.htm

Here is a link that may help?  It has been posted here before.

73 de jay/w5jay..

>I have been using SO2R in some of the RTTY contests for several years now.
>When I first set it up I was concerned about blowing the front end
>transistors in my (then) paired ICOM 756PRO radios. It occurred to me that
>I could simply measure RF voltage coming back in from the "other" antenna
>when under full power and verify that I was below the voltage that might
>damage the input devices. I made up a simple 50 ohm loaded diode probe for
>the measurements with my DVM.
>
> The usual techniques of stubs and filters, along with antenna separation
> of apprx a hundred feet, yielded worst-case voltages of around 300 mv with
> 1000 watts tx'ed on the "other" antenna. I assumed this could easily be
> tolerated by the radios and so far this has proven correct through 3
> generations of different pairs of radios.
>
> I would recommend this technique of actually measuring the incoming
> voltage, then use common sense as to what levels are tolerable.  Yesterday
> Wayne gave some guidance on tolerable levels with the K3, removing some of
> the guesswork.
>
> Jerry W4UK
>
>
>>"Subject: RE: [Elecraft] Re: Question re K3 diversity reception
>>
>>Wayne,
>>To carry this one step more, what about when I am running multiple K3's on
>>different bands at the same time? Do you recommend to use external receive
>>bandpass filters on the receive lines if I am using receive antennas on
>>the
>>Receive Antenna and/or Aux input?
>>And also use transmit bandpass filters on the transmit antenna input when
>>I
>>am using the transmit antenna for both receive and transmit?"
>>
>>
>>Julius Fazekas
>>N2WN
>>
>>Tennessee Contest Group
>
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