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two k3's on the same band

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Matt Murphy

two k3's on the same band

Just wondering if anyone has any experience using two K3's on the same band
(for example, one for running, one for mults in a multi-op single
transmitter scenario). Is there any danger of damaging the receiver(s) by
transmitting with high power so close by (different antenna, same
property). Is there a difference if the transmission is a few KHz away vs
(accidentally) on the same frequency?

Just curious what sorts of precautions (if any) ought to be taken and what
solutions exist (if necessary).

73,
Matt NQ6N
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Tom Azlin N4ZPT-2

Re: two k3's on the same band

Yes.

Vienna Wireless Society K4XY Field Day multiple times. We had an all K3
field day couple times with 2 K3s on 40m. One CW and one SSB. Antennas
were dipoles or two element wire yagis both pointing West with about 300
ft separation E-W ( yea, CW station was in the beam of the SSB station].
Either K3 could dial close to the other with little issue. When we tuned
past the other station was just a strong station. I guess plenty of one
over r-squared isolation?

73, tom n4zpt

On 3/21/2012 3:24 PM, Matt Murphy wrote:

> Just wondering if anyone has any experience using two K3's on the same band
> (for example, one for running, one for mults in a multi-op single
> transmitter scenario). Is there any danger of damaging the receiver(s) by
> transmitting with high power so close by (different antenna, same
> property). Is there a difference if the transmission is a few KHz away vs
> (accidentally) on the same frequency?
>
> Just curious what sorts of precautions (if any) ought to be taken and what
> solutions exist (if necessary).
>
> 73,
> Matt NQ6N
> ______________________________________________________________
> Elecraft mailing list
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>
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>
>

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Arie Kleingeld PA3A-2

Re: two k3's on the same band

In reply to this post by Matt Murphy

Matt,

At PI4D we have two beams that can work on 20m: a 5L monobander and a
FB-53 (5L tribander).
The beams are about 75m (220ft) apart. Worst case scenario(beams
pointing towards each other):
running 1kW in the monobander we measured a 9W signal on the FB-53.

Yes, you have to take precautions.
We did this once. Solution: when one station is on the air, the other is
keyed by ptt (shutting down the RX) without possibility
for transmission (disconnecting ptt of the linear amp and the
microphone- and cw-inputs).
Worked just fine.

73,
Arie PA3A

Op 21-3-2012 20:24, Matt Murphy schreef:

Milt -- N5IA

Re: two k3's on the same band

In reply to this post by Matt Murphy

Matt,

The multi-op NI5T operation in the CQ 160 contests at the N5BG station are
done in the manner you are inquiring about.

We run THREE K3s, one running and two S&P on Topband, all three transmitting
with full 1.5 kW output power.

Granted, we exclusively use Beverage antennas for receiving, and the
Beverage field is at some distance from the TX antenna.

We copy stations with the S&P positions to within a few kHz of the CQing
position.

Many times we operate in full duplex on the same freq, with one of the S&P
positions listening on the CQ frequency in a different direction than the CQ
position is listening. This allows us to listen in multiple directions with
the Beverages.

We do not and have never had any problem doing this with the K3s or with the
lineup of FT-1000 MPs we previously used. Never a single instance of
receiver damage while operating in this manner the past ~13 years.

The KEY to successful in-band duplex operation is ISOLATION, either by
polarity or physical antenna separation, or both.

YMMV, and good luck with your trial.

73 de Milt, N5IA

-----Original Message-----
From: Matt Murphy
Sent: Wednesday, March 21, 2012 12:24 PM
To: Elecraft Reflector
Subject: [Elecraft] two k3's on the same band

Just wondering if anyone has any experience using two K3's on the same band
(for example, one for running, one for mults in a multi-op single
transmitter scenario). Is there any danger of damaging the receiver(s) by
transmitting with high power so close by (different antenna, same
property). Is there a difference if the transmission is a few KHz away vs
(accidentally) on the same frequency?

Just curious what sorts of precautions (if any) ought to be taken and what
solutions exist (if necessary).

73,
Matt NQ6N

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Bill Frantz

Re: two k3's on the same band

In reply to this post by Matt Murphy

The West Valley Amateur Radio Association used K3s last year for
the CW part of our field day operation. We also had an active
digital station on the same band, so there was not much
frequency difference. We were operating QRP at 5 watts. I think
our antennas were closer than the 300 feet Tom, N4ZPT reported
for the Vienna Wireless Society operation.

I did not hear any complaints from the CW operators, although we
did get interference from the digital station with our SSB
operation (which was not using Elecraft equipment).

Cheers - Bill, AE6JV

On 3/21/12 at 12:24, [hidden email] (Matt Murphy) wrote:

>Just wondering if anyone has any experience using two K3's on the same band ...

-----------------------------------------------------------------------
Bill Frantz | I like the farmers' market | Periwinkle
(408)356-8506 | because I can get fruits and | 16345
Englewood Ave
www.pwpconsult.com | vegetables without stickers. | Los Gatos,
CA 95032

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Jim Brown-10

Re: two k3's on the same band

In reply to this post by Matt Murphy

On 3/21/2012 12:24 PM, Matt Murphy wrote:
> Just wondering if anyone has any experience using two K3's on the same band

YES! My first experiences were on county expeditions for the California
QSO Party, with four K3s feeding two KPA500s, a Ten Tec Herc II, and a
600W Yaesu amp. We had tribanders pointed roughly 70 degrees, carefully
located so that they were at 90 degrees to each other, and were able to
run one on CW with the other on SSB on the same band on 15 and 20M. The
stations would hear each other at about S6-7, so we could work the
roughly 60% of signals that were louder than that, then we would have
one change bands so that both could work the weaker ones.

At home, I have a 3-el SteppIR at 120 ft on one tower, monobanders for
20 and 15 at about 40 ft on a tower about 150 ft away, and a 4-el 10M
Yagi about 50 ft further from the SteppIR. During contests, I run Ten
Tec Titan amps at legal power with two K3s. All of my antennas are fed
with either CATV hard line or Heliax for most of their run, and
everything else, including all patch cables inside the shack, is on very
good RG213 with soldered Amphenol PL259s. With those Yagis optimally
aimed to reject each other, I can operate as close as 50 kHz on 20, 15,
and 10 and not know the other station is there. Pointing one at the
other is another story, and can cause the receiving K3 to turn off the
preamp and turn on the attenuator, but I can still work strong stations
through my own QRM.

I mentioned the quality of my coax because that is quite important when
you're trying to get a lot of rejection. Poor connections, or poorly
shielded coax, or both, can couple common mode current from the outside
of the coax to the inside of the coax at low levels. Coax shielding is a
function of the resistance of the shield, the density of the shield, and
the uniformity of the shield. Thanks to skin effect, the larger the
diameter of the coax the lower the RF resistance of the shield, assuming
a shield of the same quality.

73, Jim K9YC
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alorona

Re: two k3's on the same band

Jim, I think you may have answered a question that's been on my mind for years.

Some time ago an advertisement for coax cable in QST said that a certain cable
had "80 dB shielding". I had never seen a spec for this before. Could they have
been referring to the leakage from inside to outside; outside to inside (as you
were describing); or both? Or something else?

Al W6LX

> Poor connections, or poorly shielded coax,
> or both, can couple common mode current
> from the outside of the coax to the inside of
> the coax at low levels.
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k6dgw

Re: two k3's on the same band

In reply to this post by Matt Murphy

On 3/21/2012 12:24 PM, Matt Murphy wrote:
> Just wondering if anyone has any experience using two K3's on the same band
> (for example, one for running, one for mults in a multi-op single
> transmitter scenario).

Yes, accidentally at N6A in the 2011 Cal QSO Party. There was no
lockout mechanism, it was late at night, it was the first time we'd ever
done an M/2 operation, and we probably should have known better, we had
over 200 years of combined ham experience aboard.

Is there any danger of damaging the receiver(s) by
> transmitting with high power so close by (different antenna, same
> property).

Yes, we fried the PIN diodes in the K3 front end. The other rig was an
ICOM Pro and the K3 was never keyed so it survived.

Is there a difference if the transmission is a few KHz away vs
> (accidentally) on the same frequency?

Depends. The critical issue is whether or not the antennas are in each
others near field. If they are, they become coupled elements just as
parasitic elements in a beam are coupled to the driven element. Coupled
power in antenna 2 from same-band antenna 1 can then be large enough to
fry the input circuits.

The size of an antenna's near field is roughly, kind of proportional to
the gross size of the antenna. Thus, lower frequency antennas, being
larger, have a larger near field than higher frequency antennas. The
two 80/75 meter antennas [Inverted V's] at N6A were definitely in each
other's near field, something that won't happen this year. :-)

It doesn't matter where the two radios are tuned in the band. The
damage happens at the very front end, often in the diodes of the TR
switch or the first RF amp device.

If the antennas are definitely NOT in each other's near fields, you
probably won't sustain any physical damage. Whether or not the radios
can be used will then depend on their dynamic blocking and IMD
characteristics. Jack, KF6T, is about 2 km from my station and runs
legal limit. With a Kenwood TS-850, I could not operate on the same
band with him, I heard his keying all over the band at 30 over,
generated in my receiver. With my K2, I can get within 3 or 4 KHz
before I begin to hear products. With my K3, I can get within a KHz or
less.
>
> Just curious what sorts of precautions (if any) ought to be taken and what
> solutions exist (if necessary).

1. Make certain the two antennas are definitely NOT in each others near
fields. When BPL was a real possibility, I modeled the power lines near
us and my antenna with EZNEC4. It indicated a coupling factor [the loss
between my power and what would show up in the power line] of about -35
to-38 dB on all bands except 160. There, it was -15 dB, because at 160,
the antenna and the distribution lines were in each others near fields.

2. Run K3's.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

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Jim Brown-10

Re: two k3's on the same band

In reply to this post by alorona

On 3/21/2012 3:33 PM, Al Lorona wrote:
> Some time ago an advertisement for coax cable in QST said that a certain cable had "80 dB shielding".

I'd call that an advertising claim. Real specifications for this are
quantities like the Transfer Impedance, which is the ratio between the
differential voltage inside the coax as a result of current on the
outside of the coax. That ratio varies a LOT as a function of
frequency. The lower the value of that transfer impedance, the better
the shielding. The lower limit on the transfer impedance is the
resistance of the shield.

73, Jim K9YC
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k1htv

Re: two k3's on the same band

In reply to this post by Matt Murphy

Matt,
We've used two K3's on 160 Meters driving a common 1500 Watt amplifier at
W3LPL in the CQ & ARRL DX contests for the past few years with no problems.
Frank has eight 500+ feet long Beverage antennas located a couple of hundred of
feet from the 4-Square antenna. On CW the K3 op listening for mults is able to
receive on most of the Beverages as close at 10 KHz from the transmit frequency.
The K3's are isolated from the Beverages by a band pass filter and preamp.
Antennas for the other HF bands, also fed with a KW, are even closer to the
Beverages and have no effect at all on the 160M K3 transceivers. About the only
thing that will blow the preamps is a lightning strike.

At home with a barefoot K3 at 100 Watts, I feed 4 switched Beverage antennas to
the K3's sub-receiver using a common preamp. The antennas are as close as 50
feet with no sign of the overload relay clicking in.

73,
Rich - K1HTV

= = =

-----Original Message-----
From: Matt Murphy [mailto:[hidden email]]
Sent: Wednesday, March 21, 2012 15:24 PM
To: Elecraft Reflector
Subject: [Elecraft] two k3's on the same band

Just wondering if anyone has any experience using two K3's on the same band (for
example, one for running, one for mults in a multi-op single transmitter
scenario). Is there any danger of damaging the receiver(s) by transmitting with
high power so close by (different antenna, same property). Is there a
difference if the transmission is a few KHz away vs
(accidentally) on the same frequency?

Just curious what sorts of precautions (if any) ought to be taken and what
solutions exist (if necessary).

73,
Matt NQ6N

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