Home |
Search |
Today's Posts |
|
#1
![]() |
|||
|
|||
![]()
On 9/27/2015 2:20 PM, Wayne wrote:
"rickman" wrote in message ... On 9/27/2015 10:41 AM, kg7fu wrote: Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Can you explain this? I thought matching the antenna would *exactly* make the return loss go away because it would eliminate the mismatch. Not wanting to put words in his mouth.... I read that to mean that the high SWR between the ATU and the antenna would remain, but the transmitter would be happy with the SWR on the transmitter/ATU coax. Are you suggesting the ATU is at the transmitter rather than at the antenna? The losses are in the coax and transmitter. If the ATU is at the transmitter you still have coax losses. If the ATU is at the antenna there are then no losses other than due to non-ideality of the ATU. -- Rick |
#2
![]() |
|||
|
|||
![]()
rickman wrote:
On 9/27/2015 2:20 PM, Wayne wrote: "rickman" wrote in message ... On 9/27/2015 10:41 AM, kg7fu wrote: Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Can you explain this? I thought matching the antenna would *exactly* make the return loss go away because it would eliminate the mismatch. Not wanting to put words in his mouth.... I read that to mean that the high SWR between the ATU and the antenna would remain, but the transmitter would be happy with the SWR on the transmitter/ATU coax. Are you suggesting the ATU is at the transmitter rather than at the antenna? The losses are in the coax and transmitter. If the ATU is at the transmitter you still have coax losses. If the ATU is at the antenna there are then no losses other than due to non-ideality of the ATU. It was stated in the original post the ATU is at the transmitter end. -- Jim Pennino |
#3
![]() |
|||
|
|||
![]() "rickman" wrote in message ... On 9/27/2015 2:20 PM, Wayne wrote: "rickman" wrote in message ... On 9/27/2015 10:41 AM, kg7fu wrote: Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Can you explain this? I thought matching the antenna would *exactly* make the return loss go away because it would eliminate the mismatch. Not wanting to put words in his mouth.... I read that to mean that the high SWR between the ATU and the antenna would remain, but the transmitter would be happy with the SWR on the transmitter/ATU coax. # Are you suggesting the ATU is at the transmitter rather than at the # antenna? Yes. It is a whip with a 15 foot run of 213 to an ATU in the shack. The coax loss is low enough that I can live with a higher SWR. |
#4
![]() |
|||
|
|||
![]()
On 9/27/2015 1:20 PM, Wayne wrote:
"rickman" wrote in message ... On 9/27/2015 10:41 AM, kg7fu wrote: Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Can you explain this? I thought matching the antenna would *exactly* make the return loss go away because it would eliminate the mismatch. Not wanting to put words in his mouth.... I read that to mean that the high SWR between the ATU and the antenna would remain, but the transmitter would be happy with the SWR on the transmitter/ATU coax. Rick is correct. If the antenna (load) is matched to the line, there is no return loss, hence no SWR. The ATU will be adjusted (hopefully) to make the transmitter operate properly with the impedance as seen at the transmitter end of the line. Yes, the SWR due to mismatch of the antenna (load) and line will remain. Even if the real part of your load impedance is matched to the line, you will still have a high SWR if the reactance remains. Does this make sense? |
#5
![]() |
|||
|
|||
![]() "John S" wrote in message ... On 9/27/2015 1:20 PM, Wayne wrote: "rickman" wrote in message ... On 9/27/2015 10:41 AM, kg7fu wrote: Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Can you explain this? I thought matching the antenna would *exactly* make the return loss go away because it would eliminate the mismatch. Not wanting to put words in his mouth.... I read that to mean that the high SWR between the ATU and the antenna would remain, but the transmitter would be happy with the SWR on the transmitter/ATU coax. # Rick is correct. If the antenna (load) is matched to the line, there is # no return loss, hence no SWR. The ATU will be adjusted (hopefully) to # make the transmitter operate properly with the impedance as seen at the # transmitter end of the line. # Yes, the SWR due to mismatch of the antenna (load) and line will remain. # Even if the real part of your load impedance is matched to the line, you # will still have a high SWR if the reactance remains. # Does this make sense? Yes. That's what I was trying to say using SWR instead of return loss. Return loss numbers get bigger with lower SWR. For example: SWR 1:1 = infinite return loss. But I assumed that Rick was talking about the reflected power used in the return loss calculation. That part goes to zero for a perfect match, hence the infinite return loss. Since my ATU is closer to the transmitter than the antenna, I tune for lowest SWR from the transmitter to the ATU and don't worry about the ATU to antenna SWR. I believe we are all talking about the same thing. |
#6
![]() |
|||
|
|||
![]()
On 9/27/2015 1:42 PM, John S wrote:
On 9/27/2015 1:20 PM, Wayne wrote: "rickman" wrote in message ... On 9/27/2015 10:41 AM, kg7fu wrote: Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Can you explain this? I thought matching the antenna would *exactly* make the return loss go away because it would eliminate the mismatch. Not wanting to put words in his mouth.... I read that to mean that the high SWR between the ATU and the antenna would remain, but the transmitter would be happy with the SWR on the transmitter/ATU coax. Rick is correct. If the antenna (load) is matched to the line, there is no return loss, hence no SWR. The ATU will be adjusted (hopefully) to make the transmitter operate properly with the impedance as seen at the transmitter end of the line. I apologize. My statement that "there is no return loss" above is technically incorrect. The return loss with matched conditions is maximum. It will peg your meter. |
#7
![]() |
|||
|
|||
![]()
On 9/27/2015 9:41 AM, kg7fu wrote:
Doubling the number of feedlines would double the losses. Not only that but each connector in the system inserts losses so that number would be 4x. How can that be? Each line carries half the power. Connector loss at 14MHz is insignificant. Increasing the coax diameter would effectively reduce the loss. No argument here. Except that it costs much more. Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. Maybe you are working from the assumption that a mismatch between the source and line causes return loss. It does not. Only the mismatch between the load and line causes return loss. KG7FU On 09/25/2015 02:31 PM, Wayne wrote: I use a short vertical antenna that has a low feedpoint impedance. Would there be any advantage to running two parallel 50 ohm coax to reduce losses to the shack tuner? |
#8
![]() |
|||
|
|||
![]() On 09/27/2015 11:22 AM, John S wrote: On 9/27/2015 9:41 AM, kg7fu wrote: Doubling the number of feedlines would double the losses. Not only that but each connector in the system inserts losses so that number would be 4x. How can that be? Each line carries half the power. Connector loss at 14MHz is insignificant. Connector losses are static up to UHF at around .5db per connector for a typical PL-259/SO-239 pair. Insertion losses for professional grade connectors on high quality rigid and semi-rigid coax such as Andrew Heliax are around .05db. Matching the antenna won't make the Return Loss go away but it will make the transmitter happy. I should have said matching the line. Maybe you are working from the assumption that a mismatch between the source and line causes return loss. It does not. Only the mismatch between the load and line causes return loss. KG7FU |
#9
![]() |
|||
|
|||
![]() "kg7fu" wrote in message ... On 09/27/2015 11:22 AM, John S wrote: On 9/27/2015 9:41 AM, kg7fu wrote: Doubling the number of feedlines would double the losses. Not only that but each connector in the system inserts losses so that number would be 4x. How can that be? Each line carries half the power. Connector loss at 14MHz is insignificant. Connector losses are static up to UHF at around .5db per connector for a typical PL-259/SO-239 pair. Insertion losses for professional grade connectors on high quality rigid and semi-rigid coax such as Andrew Heliax are around .05db. Where did you get the .5 db loss per connector ? If you would think for about 1 minuit,you would see that has to be wrong. To make things simple and using round numbers. Take 2 PL-259 connectors and a barrel connector and put them together. Not counting the barrel that would be 1 db of loss. That is about 25 %. Using a 100 watt transmitter, that is 25 watts of heat in a couple of inches. It would get warm. Bumping it up to the 1 KW level that lots of hams use, that is 250 watts. It would melt down in a short order. The loss is around .01 db per connector around 100 MHz, about half that at 10 MHz. |
Reply |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
OT Parallel to USB Cable | CB | |||
Parallel Lines | Antenna | |||
varicaps in parallel | Homebrew | |||
varicaps in parallel | Homebrew | |||
Parallel runs of coax to antenna | Antenna |