Impedance matching by adding/subtracting open wire transmission line
A simple antenna tuner made from switches. How to determine the “best” transmission line lengths for multi-band center fed wire dipoles.
by Cecil Moore, W5DXP
“Turns the New York subway system into an interactive string instrument.”
Resistance and capacitance in an AM radio.
A first test to find out if its practical to ‘piggyback’ external controls on to an existing radio. The reason for doing this is to leave an original radio intact by clipping the remote components to the leads of the existing controls.
For example a varactor would be connected in parallel to the variable capacitor already in the circuit. The existing capacitor would be set low. The capacitance of the varactor would then be added to the total, using the formula for parallel capacitors.
For potentiometers, its not as easy because parallel resistors are divided:
Formula: Rtotal = R1×R2/(R1+R2)
For example if R1 is 10K, R2 would need to be 100K to get a total resistance of 9K. To get 99% of the existing resistance, the piggyback resistor needs to be 100 times the value of the existing resistor. 1 MegOhm if matched with 10K.
What happens when the radio is not being controlled remotely?
- For capacitance, the remote capacitor (varactor) should be set to 0.
- For resistance, the remote resistor should be set as high as possible.
Conversely, how should the physical controls on the radio be set when operating remotely?
- Variable capacitors should be set as low as possible.
- Potentiometers should be set as high as possible. For a volume control this actually means turning the volume all the way down.
SPST switches can be considered as a form of potentiometer with infinite resistance. A piggybacked switch will only work if the existing switch is in the ‘off’ position. And vice-versa.
Double-Throw and Rotary switches present more difficulties as multiple states are maintained by the same device.
I don’t think multiple throw switches can be piggybacked. Two possible solutions:
- mechanical connection to manual control (servo)
- internal relays – requiring modification of the radio, so that the existing control and the remote control operate the same relays
- Hybrid approach: Operate the switches manually while operating other controls remotely.
I piggybacked a tuning capacitor from an AM radio onto the tuning capacitor of a vintage Radio Shack Globe Patrol (regenerative receiver).
By Christopher Konopka
A soundscape that responds to color.
By Helen Trevillion
The Max patch is not available. From the video it appears that many channels of sound are playing concurrently. Color values are assigned to faders for each channel.
How to use the Max preset object inside of M4L.
There is some confusion about how to use Max presets in a M4L device. The method described here lets you save and recall presets with a device inside of a Live set, without additional files or dialog boxes. It uses pattrstorage. It works automatically with the Live UI objects.
It also works with other Max UI objects by connecting them to pattr objects.
Its based on an article by Gregory Taylor: https://cycling74.com/2011/05/19/max-for-live-tutorial-adding-pattr-presets-to-your-live-session/
How it works:
Instructions are included inside the patch. You will need to add objects and then set attributes for those objects in the inspector. For best results, set the inspector values after adding each object
Write the patch in this order:
A1. Add UI objects.
For each UI object:
- check link-to-scripting name
- set long and short names to actual name of param
A2 (optional) Add non Live (ie., Max UI objects)
For each object, connect the middle outlet of a pattr object (with a parameter name as an argument) to the left inlet of the UI object. For example:
Then in inspector for each UI object:
- check parameter-mode-enable
- check inital-enable
B. Add a pattrstorage object.
Give the object a name argument, for example: pattrstorage zoo. The name can be anything, its not important. Then in the inspector for pattrstorage:
- check parameter-mode enable
- check Auto-update-parameter Initial-value
- check initial-value
- change short-name to match long name
C. Add an autopattr object
D. Add a preset object
In the inspector for the preset object:
- assign pattrstorage object name from step B. (zoo) to pattrstorage attribute
The preset numbers go from 1-n. They can be fed directly into the pattrstorage object – for example if you wanted to use an external controller
You can name the presets (slotnames). See the pattrstorage help file
You can interpolate between presets. See pattrstorage help file
Adding new UI objects after presets have been stored
If you add a new UI object to the patch after pattrstorage is set up, you will need to re-save the presets with the correct setting of the new UI object. Or you can edit the pattrstorage data.
The Lorentz factor and its role in relativity
From “Sixty Symbols” By Brady Haran for the University of Nottingham