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rv8iator
Joined: 11 Apr 2006
Posts: 144
Location: Newberg, OR
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 Posted: Tue Dec 19, 2023 5:10 pm Post subject: Transponder dummy load |
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What is the appropriate type load to apply as a dummy in place of an antenna to test operation of a transponder?
I am about ready to close up my RV forward fuselage which restricts access to the avionics bay but want to validate the operation of all components and systems. The transponder communicates to the Echo UAT via serial connection and sends the set xponter code to the UAT. Thus I need to verify proper operation. The xponder antenna is not yet mounted on the airframe as the fuselage sits on it's belly until completion of the canopy.
...Chris
Another RV
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alfuller194(at)gmail.com
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| Posted: Tue Dec 19, 2023 5:53 pm Post subject: Transponder dummy load |
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I’m used to transmitters wanting to see 50 ohms on the antenna line, so a 50 ohm dummy load would look like an antenna to it.
That said, the documentation should tell you – or call the manufacturer…
-----------------------------------
All the best,
Al Fuller
From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Christopher Cee Stone
Sent: Tuesday, December 19, 2023 5:10 PM
To: aeroelectric-list(at)matronics.com
Subject: Transponder dummy load
What is the appropriate type load to apply as a dummy in place of an antenna to test operation of a transponder?
I am about ready to close up my RV forward fuselage which restricts access to the avionics bay but want to validate the operation of all components and systems. The transponder communicates to the Echo UAT via serial connection and sends the set xponter code to the UAT. Thus I need to verify proper operation. The xponder antenna is not yet mounted on the airframe as the fuselage sits on it's belly until completion of the canopy.
...Chris
Another RV
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rv8iator
Joined: 11 Apr 2006
Posts: 144
Location: Newberg, OR
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| Posted: Tue Dec 19, 2023 6:01 pm Post subject: Transponder dummy load |
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The load has to dissipate the power which is quite high I believe. An inductive load I don't think is advisable.
On Tue, Dec 19, 2023 at 5:55 PM <alfuller194(at)gmail.com (alfuller194(at)gmail.com)> wrote:
| Quote: |
I’m used to transmitters wanting to see 50 ohms on the antenna line, so a 50 ohm dummy load would look like an antenna to it.
Â
That said, the documentation should tell you – or call the manufacturer…
Â
-----------------------------------
All the best,
Â
Al Fuller
Â
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) <owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)> On Behalf Of Christopher Cee Stone
Sent: Tuesday, December 19, 2023 5:10 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Transponder dummy load
Â
What is the appropriate type load to apply as a dummy in place of an antenna to test operation of a transponder?
Â
I am about ready to close up my RV forward fuselage which restricts access to the avionics bay but want to validate the operation of all components and systems. The transponder communicates to the Echo UAT via serial connection and sends the set xponter code to the UAT. Thus I need to verify proper operation. The xponder antenna is not yet mounted on the airframe as the fuselage sits on it's belly until completion of the canopy.
Â
...Chris
Another RV
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nuckolls.bob(at)aeroelect
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| Posted: Wed Dec 20, 2023 4:32 am Post subject: Transponder dummy load |
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At 08:00 PM 12/19/2023, you wrote:
| Quote: | | The load has to dissipate the power which is quite high I believe. An inductive load I don't think is advisable. |
The PEAK power from a transponder is indeed
'high' . . . on the order of 150 to 200 watts.
But this is pulsed power lasting mere microseconds
per reply. Here's a narrative harvested from
the 'net . . .
-----*****-----
http://tinyurl.com/nhde9dx3
Transponders have a low duty cycle. It is limited to 4.5% but
that typically only occurs in high interrogation airspace
(an area with a large number of secondary surveillance
radars and TCAS equipped aircraft.) A typical duty cycle is in the range of 1% to 2%.
ADS-B Mode S extended squitters are 120 usec long and consist
of 120 half usec long pulses. So that's equivalent to 0.006%
duty cycle for one reply per second. Between interrogation
replies (which are about half the length of ADS-B outputs)
and ADS-B squitters you're looking at typically 200 to 250
transmissions per sec resulting in a bit over 1% duty cycle.
Transponders typically use capacitors to store up power and
a switching power supply to drive the transmitter. Even
with an efficiency of 50% (not uncommon in many RF transmitters)
you only need an average input of 3 Watts transmit 150W 1%
of the time.. At the limit of 4% duty cycle, the power needed
would be 12W (but only for a few seconds as the maximum duty
cycle only has to be sustained for a few seconds.)
So, yes it is possible to have a transponder only need
an average input power of 12W.
-----*****-----
Hence, dummy load requirements are quite benign.
Here's a suitable candidate:
https://tinyurl.com/ysxq28na
Good to add to your toolbox. It's suitable for
terminating ANY of your RF emitters such as
VHF Comm, TCAS, ELT, etc. etc.
I've got several such devices that range from
milliwatts up to hundreds of watts.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
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henador_titzoff(at)yahoo.
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| Posted: Wed Dec 20, 2023 5:17 am Post subject: Transponder dummy load |
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Chris,
The answer you are seeking is in the Echo UAT Installation and User Guide, Section 7.1.1, Antenna Cable. It lists this cable as having three characteristics with one having an impedance of 50 Ohms. This document can be found at the Echo UAT website under Documentation -> Install Manual.
https://uavionix.com/downloads/echo-uat/echoUAT-User-and-Installation-Guide.pdf
50 Ohms is the standard impedance for high power transmission through a cable. The following link tells you why. It is based on the research of two Bell Labs engineers who were interested in transmitting telephony high power for long distances back in 1929. The graph you see shows attenuation, voltage and power as functions of cable impedance. It explains that 50 Ohms is a compromise between 50 and 75 Ohms. You can see that 75 Ohms, another common cable standard, results in minimum attenuation. 75 Ohms is ideal for transmitting lower power with minimum attenuation. Voltage is a concern, because it can cause arcing between the center wire and shield through the dialectric. That's why high power 50 Ohms backs off from the minimum attenuation.
https://antenna-handbook.blogspot.com/2018/09/why-50-ohm-impedance-cable-ideal-for.html
I hope this helps you.
Simon Ramirez
On Dec 19, 2023 at 9:00 PM, Christopher Cee Stone <rv8iator(at)gmail.com> wrote: | Quote: | ">The load has to dissipate the power which is quite high I believe. An inductive load I don't think is advisable.
On Tue, Dec 19, 2023 at 5:55 PM <alfuller194(at)gmail.com (alfuller194(at)gmail.com)> wrote:
| Quote: |
I’m used to transmitters wanting to see 50 ohms on the antenna line, so a 50 ohm dummy load would look like an antenna to it.
That said, the documentation should tell you – or call the manufacturer…
-----------------------------------
All the best,
Al Fuller
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) <owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)> On Behalf Of Christopher Cee Stone
Sent: Tuesday, December 19, 2023 5:10 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Transponder dummy load
What is the appropriate type load to apply as a dummy in place of an antenna to test operation of a transponder?
I am about ready to close up my RV forward fuselage which restricts access to the avionics bay but want to validate the operation of all components and systems. The transponder communicates to the Echo UAT via serial connection and sends the set xponter code to the UAT. Thus I need to verify proper operation. The xponder antenna is not yet mounted on the airframe as the fuselage sits on it's belly until completion of the canopy.
...Chris
Another RV
|
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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rv8iator
Joined: 11 Apr 2006
Posts: 144
Location: Newberg, OR
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| Posted: Wed Dec 20, 2023 6:31 am Post subject: Transponder dummy load |
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Bob, Thanks for the info. I have lots of 50Ω terminations from the old coax network days. But not designed for high power.The item you referred is exactly what I need! Â
...chris
On Wed, Dec 20, 2023 at 4:35 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 08:00 PM 12/19/2023, you wrote:
| Quote: | | The load has to dissipate the power which is quite high I believe. An inductive load I don't think is advisable. |
 The PEAK power from a transponder is indeed
 'high' . . . on the order of 150 to 200 watts.
 But this is pulsed power lasting mere microseconds
 per reply. Here's a narrative harvested from
 the 'net . . .
-----*****-----
http://tinyurl.com/nhde9dx3
Transponders have a low duty cycle. It is limited to 4.5% but
that typically only occurs in high interrogation airspace
(an area with a large number of secondary surveillance
radars and TCAS equipped aircraft.) A typical duty cycle is in the range of 1% to 2%.
ADS-B Mode S extended squitters are 120 usec long and consist
of 120 half usec long pulses. So that's equivalent to 0.006%
duty cycle for one reply per second. Between interrogation
replies (which are about half the length of ADS-B outputs)
and ADS-B squitters you're looking at typically 200 to 250
transmissions per sec resulting in a bit over 1% duty cycle.
Transponders typically use capacitors to store up power and
a switching power supply to drive the transmitter. Even
with an efficiency of 50% (not uncommon in many RF transmitters)
you only need an average input of 3 Watts transmit 150W 1%
of the time.. At the limit of 4% duty cycle, the power needed
would be 12W (but only for a few seconds as the maximum duty
cycle only has to be sustained for a few seconds.)
So, yes it is possible to have a transponder only need
an average input power of 12W.
-----*****-----
 Hence, dummy load requirements are quite benign.
 Here's a suitable candidate:
https://tinyurl.com/ysxq28na
 Good to add to your toolbox. It's suitable for
 terminating ANY of your RF emitters such as
 VHF Comm, TCAS, ELT, etc. etc.
 I've got several such devices that range from
 milliwatts up to hundreds of watts.
 Bob . . .
                  ////
                 (o o)
  ===========o00o=(_)=o00o=========
  < Go ahead, make my day . . .  >
  < show me where I'm wrong.     >
  =================================
Â
  In the interest of creative evolution
  of the-best-we-know-how-to-do based
  on physics and good practice.
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
_________________
C. Stone (RV8iator) |
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| Back to top |
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