Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[JC]

Your feedline is about 350 feet. That is (with RG213 -velocity 0,66-) close
to 1 wavelength. With 1 wavelength feedline, the TX antenna is floating when
the feedline is open in the shack.

Just wrong once more. !! 

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[JC]

Your feedline is about 350 feet. That is (with RG213 -velocity 0,66-) close
to 1 wavelength. With 1 wavelength feedline, the TX antenna is floating when
the feedline is open in the shack.


I'm sorry to say that , but the concept is wrong, the TX antenna resonance
as structure has nothing to do with the impedance. Floating the element
makes it 1/4 element, keeping it connect it works like a 1/2 wave resonant
antenna.

I presemted some solutions on my Webnair at wwwrof, still available and you
can download the slides with extra information. Like PY2XB inverted V when
disconnected from the feed line drops the noise 2 S units on the RX antenna.

Changing the impedance you can notice a change in the noise but only few
dbs.

JC
N4IS

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[Kees Nijdam]

Paul,
Your feedline is about 350 feet. That is (with RG213 -velocity 0,66-) close 
to 1 wavelength. With 1 wavelength feedline, the TX antenna is floating when 
the feedline is open in the shack.
Depending on your transceiver configuration (if the TX antenna is completely 
decoupled when using the RX antenna input) you may not even need a special 
relay.
I did it this way during many years with a TX antenna 5 meters away from my 
K9AY loops.


Kees, PE5T

--
From: "Paul Ferguson" 
Sent: Friday, September 30, 2016 9:10 PM
To: 
Subject: Topband: Modeling Transmit Antenna Affect on Rx Antenna 
Performance?



For transmit I use a 160M T antenna with on ground radials. I am
considering installing a Circle-8 receiving array such as one made by
Hi-Z. The receive array would be very close to the T, maybe within 100
feet. I am using EZNEC to see how the transmit antenna proximity
affects the pattern of the Rx array.

I have a simple EZNEC model of a 4 square Rx array. The model uses a
source on each 20-foot Rx vertical, with the pattern determined by the
phase of each source.

I put models of the T and the Rx array in the same EZNEC model. With
the source removed from the T, the radials are connected to the T
portion of the antenna. This configuration shows a big degradation in
Rx front to back ratio. If I open the T at the feed-point by either
putting in a source with zero current or simply breaking the connection
between the T and its radials, running the model shows little to no
affect on the Rx pattern.

I could use a relay at the antenna to disconnect the feed line near the
feed-point when not transmitting, but I would rather avoid the relay
because of running QSK and wanting to avoid the wiring run.

My modeling runs, using either an effectively open or shorted feed line
at the T, do not represent my real system because it is not open or
shorted. The feed is about 350 feet of coax to a K9YC-designed
common-mode choke and a 1:1.56 unun. I am wondering if there might be
value in disconnecting the feed line from the antenna and measuring the
impedance looking back into the unun/choke/coax string. Take this
impedance and add it as an RLC network connected across the feed-point
of the T antenna. My thought is this would be close to what the Rx
array is really seeing when I look for the affect of the nearby T in
the EZNEC run.

Am I on a decent path or lost in the woods?

73,
Paul, K5ESW


_
Topband Reflector Archives - http://www.contesting.com/_topband


-
Geen virus gevonden in dit bericht.
Gecontroleerd door AVG - www.avg.com
Versie: 2016.0.7797 / Virusdatabase: 4656/13119 - datum van uitgifte: 
09/30/16



_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Orientation of a 160 meter receive loop?

[wb6rse1]

The main use of the coax loop or any loop for that matter is not gain but low 
noise directivity. Placing it on a small TV rotator allows for the nully of 
local noise to help improve the SNR for the desired signal. A preamp may not be 
necessary especially of it increases the desired signal and the noise the same 
amount. As with any loop, it will interact with nearby resonant antennas and 
that can be positive or negative depending upon the orientation and distance 
between antennas.

The coax loop was my first RX only antenna at it really helped. I highly 
recommend making it rotatable because local noise sources are guaranteed to 
change.

GL - Steve WB6RSE

>> 
>> Thanks, in advance for any 'advice' or reaffirmation I am on solid` ground 
>> here.
>> 
>> 72 de Jim Rodenkirch K9JWV

_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[Guy Olinger K2AV]

Hi Paul,

Modeling the effect of the feedline and the receiver terminating the
feedline is tricky. Some are able to short or open the TX feedline in the
shack due to a "favorable" length from the antenna to the shack. The brute
force method is to install a vacuum relay at the feedpoint which leaves the
feedpoint hanging on RX. That's tough for QSK, but can be done based on a
microHam or WinKey box, used as keyer both to paddle and contest software.

You also need to consult the mfr of the RX array which may have limits to
the amount of induced voltage to the Hi-Z. So until determined otherwise,
you have a TX bothering RX on TX issue in addition to a TX bothering RX on
RX issue.

73, Guy.


On Fri, Sep 30, 2016 at 3:20 PM, JC  wrote:

> My TX antenna is 60ft from my vertical WF and my horizontal WF is at the
> top
> of my TX antenna.  I am using a Folded Unipole configuration, it is  a
> skirt
> with 3 wires forming a cage.  The skirt detune the tower during RX and help
> the TX with a huge broad band.
>
> In your case, just open the T disconnecting it from the coaxial cable using
> a fast vacuum relay. This will to the same as my UNIPOLE.  Just keep the T
> floating during RX.
>
> 73
> JC
> N4IS
>
>
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
>
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[Lee STRAHAN]

Paul, I suggest you talk to Gary KD9SV as he built a Hi-Z around his TX 
antenna. 
  Incidentally the ground radials under the Hi-Z is not a good idea. I suspect 
you would have to use NEC4 to see the real effect of the radials. I have not 
made a test myself to see how close radials could be. Disconnecting the T 
element on one band like 160 will work for that band but likely will not work 
the same on 80 meters. Leaving it connected might be better. Same situation 
with the feedline impedance looking back toward the radio. That may change with 
band as well.
Lee  K7TJR

-Original Message-
From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Paul Ferguson
Sent: Friday, September 30, 2016 12:10 PM
To: topband@contesting.com
Subject: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

For transmit I use a 160M T antenna with on ground radials. I am considering 
installing a Circle-8 receiving array such as one made by Hi-Z. The receive 
array would be very close to the T, maybe within 100 feet. I am using EZNEC to 
see how the transmit antenna proximity affects the pattern of the Rx array.

I have a simple EZNEC model of a 4 square Rx array. The model uses a source on 
each 20-foot Rx vertical, with the pattern determined by the phase of each 
source. 

I put models of the T and the Rx array in the same EZNEC model. With the source 
removed from the T, the radials are connected to the T portion of the antenna. 
This configuration shows a big degradation in Rx front to back ratio. If I open 
the T at the feed-point by either putting in a source with zero current or 
simply breaking the connection between the T and its radials, running the model 
shows little to no affect on the Rx pattern.

I could use a relay at the antenna to disconnect the feed line near the 
feed-point when not transmitting, but I would rather avoid the relay because of 
running QSK and wanting to avoid the wiring run.

My modeling runs, using either an effectively open or shorted feed line at the 
T, do not represent my real system because it is not open or shorted. The feed 
is about 350 feet of coax to a K9YC-designed common-mode choke and a 1:1.56 
unun. I am wondering if there might be value in disconnecting the feed line 
from the antenna and measuring the impedance looking back into the 
unun/choke/coax string. Take this impedance and add it as an RLC network 
connected across the feed-point of the T antenna. My thought is this would be 
close to what the Rx array is really seeing when I look for the affect of the 
nearby T in the EZNEC run.

Am I on a decent path or lost in the woods?

73,
Paul, K5ESW


_
Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[JC]

My TX antenna is 60ft from my vertical WF and my horizontal WF is at the top
of my TX antenna.  I am using a Folded Unipole configuration, it is  a skirt
with 3 wires forming a cage.  The skirt detune the tower during RX and help
the TX with a huge broad band. 

In your case, just open the T disconnecting it from the coaxial cable using
a fast vacuum relay. This will to the same as my UNIPOLE.  Just keep the T
floating during RX.

73
JC
N4IS


_
Topband Reflector Archives - http://www.contesting.com/_topband

Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?

[Paul Ferguson]

For transmit I use a 160M T antenna with on ground radials. I am 
considering installing a Circle-8 receiving array such as one made by 
Hi-Z. The receive array would be very close to the T, maybe within 100 
feet. I am using EZNEC to see how the transmit antenna proximity 
affects the pattern of the Rx array.

I have a simple EZNEC model of a 4 square Rx array. The model uses a 
source on each 20-foot Rx vertical, with the pattern determined by the 
phase of each source. 

I put models of the T and the Rx array in the same EZNEC model. With 
the source removed from the T, the radials are connected to the T 
portion of the antenna. This configuration shows a big degradation in 
Rx front to back ratio. If I open the T at the feed-point by either 
putting in a source with zero current or simply breaking the connection 
between the T and its radials, running the model shows little to no 
affect on the Rx pattern.

I could use a relay at the antenna to disconnect the feed line near the 
feed-point when not transmitting, but I would rather avoid the relay 
because of running QSK and wanting to avoid the wiring run.

My modeling runs, using either an effectively open or shorted feed line 
at the T, do not represent my real system because it is not open or 
shorted. The feed is about 350 feet of coax to a K9YC-designed 
common-mode choke and a 1:1.56 unun. I am wondering if there might be 
value in disconnecting the feed line from the antenna and measuring the 
impedance looking back into the unun/choke/coax string. Take this 
impedance and add it as an RLC network connected across the feed-point 
of the T antenna. My thought is this would be close to what the Rx 
array is really seeing when I look for the affect of the nearby T in 
the EZNEC run.

Am I on a decent path or lost in the woods?

73,  
Paul, K5ESW


_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Orientation of a 160 meter receive loop?

[K4SAV]

I goofed with those gain numbers. Forgot to do the average gain test in 
EZNEC.  The program was making big errors due to too many segments.


The real answer is that there is only 2.4 dB less gain for the 
horizontal loop.


Jerry, K4SAV


On 9/30/2016 9:50 AM, K4SAV wrote:
A small loop mounted horizontally will be omnidirectional, mostly 
horizontally polarized and with a null overhead.  An omnidirectional 
antenna isn't usually a very low noise receiving antenna.  The gain 
will drop by a lot if the antenna is at low heights.  A square loop 5 
ft on a side placed horizontally at 10 ft above average ground should 
have a peak gain of about -44 dBi at 44 degrees elevation on 160 
meters.  The same loop mounted vertically with the top of the antenna 
at 10 ft (either apex up or top flat) should have a gain of about -25 
dBi.


Jerry, K4SAV

On 9/30/2016 8:03 AM, James Rodenkirch wrote:
I have a 160 meter rcv loop - kc2tx product - I want to employ this 
season.


I don't have a lot of band noise here in s/w Utah and don't want to 
bother with a rotor socan I mount the loop in a horizontal 
configuration and expect some improvement in rcv signal strength? I 
seem to recall Tom, W8JI, cautioning me to ensure I have the loop 
perfectly level. I do have a kd9sv preamp to employ and the Zo at the 
antenna is 50 ohms (verified on my Autek ant analyzer) so I can use 
50 coax for the feedline.


Thanks, in advance for any 'advice' or reaffirmation I am on solid` 
ground here.


72 de Jim Rodenkirch K9JWV
_
Topband Reflector Archives - http://www.contesting.com/_topband


_
Topband Reflector Archives - http://www.contesting.com/_topband


_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Orientation of a 160 meter receive loop?

[K4SAV]

A small loop mounted horizontally will be omnidirectional, mostly 
horizontally polarized and with a null overhead.  An omnidirectional 
antenna isn't usually a very low noise receiving antenna.  The gain will 
drop by a lot if the antenna is at low heights.  A square loop 5 ft on a 
side placed horizontally at 10 ft above average ground should have a 
peak gain of about -44 dBi at 44 degrees elevation on 160 meters.  The 
same loop mounted vertically with the top of the antenna at 10 ft 
(either apex up or top flat) should have a gain of about -25 dBi.


Jerry, K4SAV

On 9/30/2016 8:03 AM, James Rodenkirch wrote:

I have a 160 meter rcv loop - kc2tx product - I want to employ this season.

I don't have a lot of band noise here in s/w Utah and don't want to bother with 
a rotor socan I mount the loop in a horizontal configuration and expect 
some improvement in rcv signal strength? I seem to recall Tom, W8JI, cautioning 
me to ensure I have the loop perfectly level. I do have a kd9sv preamp to 
employ and the Zo at the antenna is 50 ohms (verified on my Autek ant analyzer) 
so I can use 50 coax for the feedline.

Thanks, in advance for any 'advice' or reaffirmation I am on solid` ground here.

72 de Jim Rodenkirch K9JWV
_
Topband Reflector Archives - http://www.contesting.com/_topband


_
Topband Reflector Archives - http://www.contesting.com/_topband

Topband: Orientation of a 160 meter receive loop?

[James Rodenkirch]

I have a 160 meter rcv loop - kc2tx product - I want to employ this season.

I don't have a lot of band noise here in s/w Utah and don't want to bother with 
a rotor socan I mount the loop in a horizontal configuration and expect 
some improvement in rcv signal strength? I seem to recall Tom, W8JI, cautioning 
me to ensure I have the loop perfectly level. I do have a kd9sv preamp to 
employ and the Zo at the antenna is 50 ohms (verified on my Autek ant analyzer) 
so I can use 50 coax for the feedline.

Thanks, in advance for any 'advice' or reaffirmation I am on solid` ground here.

72 de Jim Rodenkirch K9JWV
_
Topband Reflector Archives - http://www.contesting.com/_topband