Today's Message Index:
----------------------
1. 04:32 AM - Re: Transponder dummy load (Robert L. Nuckolls, III)
2. 04:48 AM - Dummy loads (fyi) (Robert L. Nuckolls, III)
3. 05:17 AM - Re: Transponder dummy load (S Remerez)
4. 06:31 AM - Re: Transponder dummy load (Christopher Cee Stone)
5. 06:39 AM - Re: Dummy loads (fyi) (Christopher Cee Stone)
6. 10:55 AM - Proper Grounding? ()
7. 11:28 AM - Re: Proper Grounding? (M Wilson)
8. 05:27 PM - Non-aircraft question (OK, maybe a plane with a galley) (Dave Saylor)
9. 07:18 PM - Re: Non-aircraft question (OK, maybe a plane with a galley) (Eric Page)
Message 1
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| Subject: | Re: Transponder dummy load |
At 08:00 PM 12/19/2023, you wrote:
>The load has to dissipate=C2 the power which=C2 is
>quite high I believe.=C2 An inductive load I don't think is=C2 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.
Message 2
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| Subject: | Dummy loads (fyi) |
>
> 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.
Dummy loads are available for a huge
range of power. Some are fitted with
power meters. Here's one example.
http://tinyurl.com/253rwzaf
These devices will indicate power output
for the system under test. They're
rated for up to 40 watts full scale.
Attached to your VHF Comm transmitter,
they would read something on the order
of 5 to 10 watts AVERAGE POWER while
transmitting.
Attached to a REALLY excited transponder,
you would barely see the needle wiggle.
Another data point for testing a powered
up transponder. It doesn't put out any
signal until interrogated by a surveilling
ground station . . . this is what triggers
the 'reply' annunciator. So unless your
reply light is active, the dummy load has
nothing to do. The dummy load also prevents
the transponder from SEEING a ground
station. So even when testing in
vicinity of such facilities, the dummy
load prevents the transponder
from reacting to radar interrogation
pulses.
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.
Message 3
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| Subject: | Re: Transponder dummy load |
Chris,
The answer you are seeking is in the Echo UAT Installation and User Guide,
Section 7.1.1, Antenna Cable.=C2- It lists this cable as having three cha
racteristics with one having an impedance of 50 Ohms.=C2- This document c
an 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 cab
le.=C2- The following link tells you why.=C2- It is based on the resear
ch of two Bell Labs engineers who were interested in transmitting telephony
high power for long distances back in 1929.=C2- The graph you see shows
attenuation, voltage and power as functions of cable impedance.=C2- It ex
plains that 50 Ohms is a compromise between 50 and 75 Ohms.=C2- You can s
ee that 75 Ohms, another common cable standard, results in minimum attenuat
ion.=C2- 75 Ohms is ideal for transmitting lower power with minimum atten
uation.=C2- Voltage is a concern, because it can cause arcing between the
center wire and shield through the dialectric.=C2- 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-id
eal-for.html
I hope this helps you.
Simon Ramirez
On Dec 19, 2023 at 9:00 PM, Christopher Cee Stone <rv8iator@gmail.com> wrot
e:
The load has to dissipate=C2-the power which=C2-is quite high I believe
.=C2- An inductive load I don't think is=C2- advisable.
On Tue, Dec 19, 2023 at 5:55=AFPM <alfuller194@gmail.com> wrote:
I=99m 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.
=C2-
That said, the documentation should tell you =93 or call the manufact
urer
=C2-
-----------------------------------
All the best,
=C2-
Al Fuller
=C2-
From: owner-aeroelectric-list-server@matronics.com <owner-aeroelectric-list
-server@matronics.com> On Behalf Of Christopher Cee Stone
Sent: Tuesday, December 19, 2023 5:10 PM
Subject: AeroElectric-List: Transponder dummy load
=C2-
What is the appropriate type load to apply as a dummy in place of an antenn
a to test operation of a transponder?
=C2-
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 an
d systems.=C2- The transponder communicates to the Echo UAT via serial co
nnection and sends the set xponter code to the UAT.=C2- Thus I need to ve
rify proper operation.=C2- The xponder antenna is not yet mounted on the
airframe as the fuselage=C2-sits on it's belly until completion of the ca
nopy.
=C2-
...Chris
Another RV
Message 4
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| Subject: | Re: Transponder dummy load |
Bob, Thanks for the info. I have lots of 50=CE=A9 terminations from the ol
d
coax network days. But not designed for high power.
The item you referred is exactly what I need!
...chris
On Wed, Dec 20, 2023 at 4:35=AFAM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 08:00 PM 12/19/2023, you wrote:
>
> The load has to dissipate=C3=82 the power which=C3=82 is quite high I bel
ieve.=C3=82 An
> inductive load I don't think is=C3=82 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 <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.
>
Message 5
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| Subject: | Re: Dummy loads (fyi) |
Bob,
Excellent info. I'm a bit smarter now, a good thing! As are others
reading this!
.chris
On Wed, Dec 20, 2023 at 4:50=AFAM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
>
> 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.
>
>
> Dummy loads are available for a huge
> range of power. Some are fitted with
> power meters. Here's one example.
>
> http://tinyurl.com/253rwzaf
>
> These devices will indicate power output
> for the system under test. They're
> rated for up to 40 watts full scale.
>
> Attached to your VHF Comm transmitter,
> they would read something on the order
> of 5 to 10 watts AVERAGE POWER while
> transmitting.
>
> Attached to a REALLY excited transponder,
> you would barely see the needle wiggle.
>
> Another data point for testing a powered
> up transponder. It doesn't put out any
> signal until interrogated by a surveilling
> ground station . . . this is what triggers
> the 'reply' annunciator. So unless your
> reply light is active, the dummy load has
> nothing to do. The dummy load also prevents
> the transponder from SEEING a ground
> station. So even when testing in
> vicinity of such facilities, the dummy
> load prevents the transponder
> from reacting to radar interrogation
> pulses.
>
>
> 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.
>
Message 6
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| Subject: | Proper Grounding? |
When I was wiring up a Trio autopilot on my kit, I noticed that the ground
wire was already grounded by checking for continuity with an ohm meter. It
appears to be grounded through the metal case of the unit to the panel. Is
that okay? Should I hook up the ground wire anyway? It seems that could
draw unwanted current through the unit.
Also, when I was wiring up the control cable to the servo, I noticed that
the shield was grounded at both ends. Originally, I thought that was the
cause of the case grounding above so I snipped it at the autopilot end. Is
that okay or should I reconnect it?
Thanks
Brad Kunkel
Message 7
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| Subject: | Re: Proper Grounding? |
I would tie the ground pin (signal ground) to ground regardless of whether
it is tied internally to case ground.
Snipping=C2- the shield ground on one side is appropriate.=C2- Don't re
-connect, this prevents the shield acting as a current path.=C2-
On Wednesday, December 20, 2023 at 01:05:03 PM CST, bk@bradkunkel.com <
bk@bradkunkel.com> wrote:
When I was wiring up a Trio autopilot on my kit, I noticed that the ground
wire was already grounded by checking for continuity with an ohm meter.=C2
- It appears to be grounded through the metal case of the unit to the pan
el.=C2- Is that okay?=C2- Should I hook up the ground wire anyway?=C2
- It seems that could draw unwanted current through the unit.
=C2-
Also, when I was wiring up the control cable to the servo, I noticed that t
he shield was grounded at both ends.=C2- Originally, I thought that was t
he cause of the case grounding above so I snipped it at the autopilot end.
=C2- Is that okay or should I reconnect it?
=C2-
Thanks
Brad Kunkel
=C2-
Message 8
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| Subject: | Non-aircraft question (OK, maybe a plane with a galley) |
I'm trying to troubleshoot my microwave oven. I was able to identify and
replace a failed capacitor. But it still has the same problem in that it
makes a loud buzz for half a second, then blows the house breaker or the
internal 20A fuse.
I tested the magnetron for an open circuit, it tests OK according to a few
sources on the internet: about one ohm across the terminals.
These diodes are attached to the capacitor terminals. When testing, I
can't get my DMM to say anything but OL. I tried diode/beep continuity
mode and regular resistance mode but both just say OL, same for the new
parts and the old parts.
I don't recognize the nose-to-nose diode symbol. I assumed the big arrow
points to what would be the banded end on the replacement.
The replacement says "2X062H" on the package and in the sales description,
but "6X3PI" printed on the body. The replacement is cylindrical while the
original is a long box.
If someone can help me out I'll make popcorn for ya! Any ideas before I
scrap this thing?
--Dave
Old diodes:
[image: image.png]
Same old diodes:
[image: image.png]
New diodes:
[image: image.png]
Message 9
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| Subject: | Re: Non-aircraft question (OK, maybe a plane with a |
galley)
Unidirectional high voltage diodes like the CL01-12 in your oven, when paired with
the HV capacitor, form a voltage-doubler that raises the transformer's ~2kV
output to ~4kV to drive the magnetron. These diodes have a forward voltage
that's too high for a DMM to test, as it can't check any diode with a forward
voltage higher than it's own battery supply.
Here's a short video that shows how to check a HV diode: https://www.youtube.com/watch?v=Cx8Q5crqKaw
The "SK" (Sanken) 2X062H is a bidirectional HV diode. Very difficult to test,
as its breakdown voltage is something like 5-6kV in one direction and 1.5-1.7kV
in the other. Its purpose is to protect the transformer and capacitor by blowing
the fuse if the magnetron develops a short circuit (in a healthy oven, it
does absolutely nothing). The 6X2P1 is a replacement for the 2X062H. Sanken's
website has no listing for the 2X062H; it appears to be obsolete.
You can check if one diode in the bidirectional package has failed short by doing
the same test as shown in the video above, in both directions. If you can
get a voltage reading in one direction, then the opposite-facing diode has shorted.
Here's a video on testing the transformer windings: https://www.youtube.com/watch?v=rtzPCItrcr8
And finally, here's a video showing how to test the magnetron: https://www.youtube.com/watch?v=_Oriae3-N8c
Resistance between the HV terminals is only half of the story, so be sure to do
the second test in the magnetron video. They can also fail by developing a current
path from a HV terminal to their metal case. This will bring the bidirectional
diode into play, which would explain your oven's symptoms. If you blew
the breaker with the new diodes installed then it's likely that they were damaged,
so be sure to test them again before you do another powered test.
-Eric
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=512826#512826
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