Re: Topband: Detuning transmit antenna in receive
A previous edition (and maybe the current one) of the Low Band DXing book has several methods of detuning TX antennas...might be worth a look. Some can be done right in the shack. 73 Charlie, N0TT On Sun, 17 Jun 2012 13:37:55 -0700 Bob K6UJ writes: > I am very interested in this subject, I am trying to figure out how > to detune my 160 inverted L.I am using a flag antenna for > receive and unfortunately > it is only about 50 feet from the base of the L.By itself the > flag works very well at reducing the local electrical noise, (which > luckily it is coming from only one direction) > When the L is strung up it the flag is useless, it reradiates the > noise like mad. I'm hoping to learn more solutions on detuning > xmit antennas during receive from the group. > Wouldn't it be nice if all we had to do was ground the feedline to > the xmit antenna during receive ? sigh I > guess the idea is to make the xmit antenna non resonant anywhere > near > the operating freq during receive. > > Bob > K6UJ > > On Jun 17, 2012, at 8:03 AM, W2XJ wrote: > > > There is no single solution for detuning an antenna it depends on > > > electrical length. For verticals a quarter wavelength or less it > is > > common to have a contactor between the network and the radiating > element > > and open the connection to float that element. This is the > practice in > > commercial directional arrays where some tower are not used in a > day or > > night mode. This does not work well on taller towers and I do not > know > > offhand how it would work with the T. It is easy enough to model > in EZNEC. > > > > On 6/16/12 3:02 PM, Shoppa, Tim wrote: > >> OK, several folks came back and recommended detuning my transmit > antenna in receive. > >> > >> Certainly any receive antenna I have is going to be in the shadow > of my transmit antenna, a 130-foot flat-top about 85 feet up, fed > against ground. (Really it's an 80 meter doublet fed with ladder > line. I tie the ladder line together at the bottom and feed against > ground.) > >> > >> Trying to figure out what "detune" is. > >> > >> I match the transmit antenna to 50 ohm coax with a L network at > the bottom. If I want to detune, then I can open up the > connection between the antenna and the L network at the bottom? > Unhook the L or C in the L network? Short out the antenna where it > comes into the L network? I could rig up a relay contact to do any > of those. > >> > >> Tim N3QE > >> ___ > >> UR RST IS ... ... ..9 QSB QSB - hw? BK > >> > > ___ > > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
The easy way to do that is with a relay between the coax center conductor and the L wire at the feedpoint. When the relay is open, that makes the L a 1/4 wave on 160 which is not self-resonant. The quarter wave is only resonant in conjunction with whatever counterpoise you are using for the L. 73, Guy. On Sun, Jun 17, 2012 at 4:37 PM, Bob K6UJ wrote: > I am very interested in this subject, I am trying to figure out how to > detune my 160 inverted L.I am using a flag antenna for receive and > unfortunately > it is only about 50 feet from the base of the L.By itself the flag > works very well at reducing the local electrical noise, (which luckily it > is coming from only one direction) > When the L is strung up it the flag is useless, it reradiates the noise > like mad. I'm hoping to learn more solutions on detuning xmit antennas > during receive from the group. > Wouldn't it be nice if all we had to do was ground the feedline to the > xmit antenna during receive ? sigh I guess the idea > is to make the xmit antenna non resonant anywhere near > the operating freq during receive. > > Bob > K6UJ > > On Jun 17, 2012, at 8:03 AM, W2XJ wrote: > > > There is no single solution for detuning an antenna it depends on > > electrical length. For verticals a quarter wavelength or less it is > > common to have a contactor between the network and the radiating element > > and open the connection to float that element. This is the practice in > > commercial directional arrays where some tower are not used in a day or > > night mode. This does not work well on taller towers and I do not know > > offhand how it would work with the T. It is easy enough to model in > EZNEC. > > > > On 6/16/12 3:02 PM, Shoppa, Tim wrote: > >> OK, several folks came back and recommended detuning my transmit > antenna in receive. > >> > >> Certainly any receive antenna I have is going to be in the shadow of my > transmit antenna, a 130-foot flat-top about 85 feet up, fed against ground. > (Really it's an 80 meter doublet fed with ladder line. I tie the ladder > line together at the bottom and feed against ground.) > >> > >> Trying to figure out what "detune" is. > >> > >> I match the transmit antenna to 50 ohm coax with a L network at the > bottom. If I want to detune, then I can open up the connection between > the antenna and the L network at the bottom? Unhook the L or C in the L > network? Short out the antenna where it comes into the L network? I could > rig up a relay contact to do any of those. > >> > >> Tim N3QE > >> ___ > >> UR RST IS ... ... ..9 QSB QSB - hw? BK > >> > > ___ > > UR RST IS ... ... ..9 QSB QSB - hw? BK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
My tower shunt feed for 160 and 80 is latching relay remote controlled. On 160, certain orientations of my very close RX flag result in reduced signal due to the influence of the tuned vertical. In those instances, I "detune" the shunt by selecting 80m. My amp has a rather dramatic way of reminding me if I fail to switch the shunt back to 160 when transmitting. Just one station's solution. 73 - Steve WB6RSE ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
I am very interested in this subject, I am trying to figure out how to detune my 160 inverted L.I am using a flag antenna for receive and unfortunately it is only about 50 feet from the base of the L.By itself the flag works very well at reducing the local electrical noise, (which luckily it is coming from only one direction) When the L is strung up it the flag is useless, it reradiates the noise like mad. I'm hoping to learn more solutions on detuning xmit antennas during receive from the group. Wouldn't it be nice if all we had to do was ground the feedline to the xmit antenna during receive ? sigh I guess the idea is to make the xmit antenna non resonant anywhere near the operating freq during receive. Bob K6UJ On Jun 17, 2012, at 8:03 AM, W2XJ wrote: > There is no single solution for detuning an antenna it depends on > electrical length. For verticals a quarter wavelength or less it is > common to have a contactor between the network and the radiating element > and open the connection to float that element. This is the practice in > commercial directional arrays where some tower are not used in a day or > night mode. This does not work well on taller towers and I do not know > offhand how it would work with the T. It is easy enough to model in EZNEC. > > On 6/16/12 3:02 PM, Shoppa, Tim wrote: >> OK, several folks came back and recommended detuning my transmit antenna in >> receive. >> >> Certainly any receive antenna I have is going to be in the shadow of my >> transmit antenna, a 130-foot flat-top about 85 feet up, fed against ground. >> (Really it's an 80 meter doublet fed with ladder line. I tie the ladder line >> together at the bottom and feed against ground.) >> >> Trying to figure out what "detune" is. >> >> I match the transmit antenna to 50 ohm coax with a L network at the bottom. >> If I want to detune, then I can open up the connection between the >> antenna and the L network at the bottom? Unhook the L or C in the L network? >> Short out the antenna where it comes into the L network? I could rig up a >> relay contact to do any of those. >> >> Tim N3QE >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
If its RF that is a concern the only positive method would be feeding it into a 50/75 Ohm resistor when transmitting. I had to do that some years ago when a Beverage ran between the phased vertical pair and after cooking a few parts in a TS-940. Beverages are now well away from any TX antennas. Carl KM1H - Original Message - From: "W2XJ" To: Sent: Sunday, June 17, 2012 11:03 AM Subject: Re: Topband: Detuning transmit antenna in receive > There is no single solution for detuning an antenna it depends on > electrical length. For verticals a quarter wavelength or less it is > common to have a contactor between the network and the radiating element > and open the connection to float that element. This is the practice in > commercial directional arrays where some tower are not used in a day or > night mode. This does not work well on taller towers and I do not know > offhand how it would work with the T. It is easy enough to model in EZNEC. > > On 6/16/12 3:02 PM, Shoppa, Tim wrote: >> OK, several folks came back and recommended detuning my transmit antenna >> in receive. >> >> Certainly any receive antenna I have is going to be in the shadow of my >> transmit antenna, a 130-foot flat-top about 85 feet up, fed against >> ground. (Really it's an 80 meter doublet fed with ladder line. I tie the >> ladder line together at the bottom and feed against ground.) >> >> Trying to figure out what "detune" is. >> >> I match the transmit antenna to 50 ohm coax with a L network at the >> bottom. If I want to detune, then I can open up the connection >> between the antenna and the L network at the bottom? Unhook the L or C in >> the L network? Short out the antenna where it comes into the L network? I >> could rig up a relay contact to do any of those. >> >> Tim N3QE >> ___ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1424 / Virus Database: 2433/5075 - Release Date: 06/17/12 > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
There is no single solution for detuning an antenna it depends on electrical length. For verticals a quarter wavelength or less it is common to have a contactor between the network and the radiating element and open the connection to float that element. This is the practice in commercial directional arrays where some tower are not used in a day or night mode. This does not work well on taller towers and I do not know offhand how it would work with the T. It is easy enough to model in EZNEC. On 6/16/12 3:02 PM, Shoppa, Tim wrote: > OK, several folks came back and recommended detuning my transmit antenna in > receive. > > Certainly any receive antenna I have is going to be in the shadow of my > transmit antenna, a 130-foot flat-top about 85 feet up, fed against ground. > (Really it's an 80 meter doublet fed with ladder line. I tie the ladder line > together at the bottom and feed against ground.) > > Trying to figure out what "detune" is. > > I match the transmit antenna to 50 ohm coax with a L network at the bottom. > If I want to detune, then I can open up the connection between the > antenna and the L network at the bottom? Unhook the L or C in the L network? > Short out the antenna where it comes into the L network? I could rig up a > relay contact to do any of those. > > Tim N3QE > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: Detuning transmit antenna in receive
Tim "Trying to figure out what "detune" is" Excellent question. The ground is the most important part of the T antenna, without the ground the antenna became a 1/4 element isolated from ground and wont irradiate. In order to accomplish that you need two fast vacuum relay to open the ladder line. The relay needs to be fast , 5 millisecond, slow relays will see RF and hot switch. It can damage your amp. The impedance on the feed line does not detune the antenna, short circuit the feed line does not insulate the T from the ground. You can see in my site www.n4is.com how deteriorate a RX antenna can be without detuning the TX antenna. My BigWF works very well 70 FT far from my TX antenna when detuned, the BWF is useless without detuning my TX antenna. Regards Jose Carlos N4IS ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
