Controlaire Mule transmitter output.

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Stephen D
Posts: 12
Joined: 02 Mar 2023, 20:43

Controlaire Mule transmitter output.

Post by Stephen D »

I have been troubleshooting some Controlaire “Mule” single channel radio systems. During this exercise I decided to try and measure power output of the transmitters. I built a test rig with a load resistor (49.8 ohms) and measured the Vp-p and Vrms across this resistor with my oscilloscope.

I measured all 4 of the mule transmitters and using ohms law calculated the power output. Mule #1 was measured with the original output transistor and a 2n2222 (since after measuring Mule #1 the output seamed low in comparison). Mule 4 is a “extra power” version one and it does seem to have extra power.

I have a couple of questions:
1. Does this seem like a valid method of testing?
2. Has anyone replaced the output transistor (2n3643) with good results? I was thinking of trying an NTE123, but if someone has found a suitable replacement It would save me some time figuring it out and I would appreciate it!

Thanks for your time!

Test results:
5C5079B7-468B-429B-9439-38C53D4BA7E5.jpeg
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Controlaire Mule transmitter output.

Post by Pchristy »

A whip aerial at 27 (or 35) MHz will appear to be far from a pure resistance. It will have a very significant capacitive element. This will be "tuned out" by using either a base or centre loaded aerial. IIRC, the Mule uses a base loaded setup. This means that if you simply replace the aerial with a purely resistive dummy load, you will get very misleading results.

Inductors, like the base loading coil, have an impedance that increases with frequency, so unless it is "tuned out" with an appropriate capacitor, you will almost certainly get a figure far lower than the actual power output.

You also risk frying the output transistor, though most radios were designed with enough heat-sink capacity to allow for short periods of operation with the aerial collapsed, for range checking purposes.

There is a very good "Whip Antenna Calculator" here: https://daycounter.com/Calculators/Whip ... ator.phtml

Simply put in the frequency, length and diameter and it will give you a pretty good indication of the characteristics of your aerial. For a telescopic aerial use the average diameter.

You can then produce a "synthetic" aerial, using the calculated radiation resistance along with a suitable capacitor which should give a better approximation.

Most of these older sets had fairly crude output matching circuits, so don't expect to necessarily get accurate results. You may do better measuring the DC input power to the output stage, or even better, just use a field strength meter to measure the relative power outputs rather than the actual power.

The field strength method is a far more relevant method, as - done carefully - it will take into account not only the actual power output, but also the efficiency of the matching network and aerial.

At the end of the day, what really matters is how much of the supplied power actually makes it into the ether, and that is what a field strength meter measures!

--
Pete
Stephen D
Posts: 12
Joined: 02 Mar 2023, 20:43

Re: Controlaire Mule transmitter output.

Post by Stephen D »

Thanks for your time and expertise!

My first step was to use a field strength meter and compare the results and compare them to see if any of them were down on power compared to the others. While doing this I found it was very sensitive to the outside atmosphere (dogs, cats, buildings, etc). So I set the Mules up in the same place and tried to minimize all the other variables. I got the same results that Mule 1 was down compared to the others.

I figured the base loading might have some effect on my measurements, and originally thought since I was looking at relative powers they would all have the same chance.

I will look up the formula you gave me and see if I can approximate the antenna and see if it changes the readings much.

Thanks again for your time.
rudderonlybird
Posts: 37
Joined: 17 Feb 2018, 05:07

Re: Controlaire Mule transmitter output.

Post by rudderonlybird »

There's the 'vintagercfiles' site with all kinds of manuals and neat stuff. For your Mule II, this is the info:

https://vintagercfiles.com/Files/Contro ... _Instr.pdf

As a 14-year-old kid, I assembled a kit from Local Hobby. Turns out I built the transmitter first before going after the receiver. After seeing the tiny (for the time) PC board and all the things needed to be installed, I was glad I did it that way. Had a local Ham operator tune it up for me, went out and flew it. Still have it, will send it to Jay Mendoza for a tune-up so I can fly it again.

I thought over the years, the Mule II was close to one watt, hence the reference to a mule (This transmitter really has a kick to it) but I never had a way to measure that. Hope this helps...

Marc
Stephen D
Posts: 12
Joined: 02 Mar 2023, 20:43

Re: Controlaire Mule transmitter output.

Post by Stephen D »

Marc,
I do actually wish I had your experience building the mule….! This was supposed to be an exercise to try and determine the best new power output replacement transistor for it then compare the output to one that I know has good range.

I originally did this by “wavemeter”…(old term)…basically an rf meter. This measurement seemed very influenced by position (and position of someone reading the meter)….and other factors. So I tried to come up with a comparison.

Thanks for the link…! I do know about “vintagercfiles”…trying to work on this stuff would not be possible without them!

Good thing you did the transmitter first! Those receivers are a lot more compact….I just went through 3 of them….(new wires on everything, new electrolytics, and one got the total rebuild (totally smashed)…so it got all new components except for transformers, chokes, and transistors….(I eventually replaced the rf transistor) and it is the one that I still can’t get any range out of….☹️ …I will eventually get there!
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Wayne_H
Posts: 810
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
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Re: Controlaire Mule transmitter output.

Post by Wayne_H »

I have a brand new assembled Mule tx board - free to a good home for the cost of postage. I'm in Australia so international postage will be about $20 - $25 I'm guessing.

I can get a more accurate estimate if you are genuinely interested, just need your address. PM me if interested.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
tedbmoss
Posts: 10
Joined: 15 Oct 2020, 07:00
Location: peoria, az

Re: Controlaire Mule transmitter output.

Post by tedbmoss »

My Mule Tx. has a center loaded antenna. I built it when I was 14 , in 1957. I used pulse proportional (mostly single channel rudder). I tried rudder and elevator with mixed results. I also had a Berkley Super-Aerotrol Tx. and super-regen Rx. with an escapement. This used a Rayathon RK-61 or an XFG-1 gas tube. (valve).
mule tx.jpg
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