modifying my TTI TCB550 to drive a deviation meter from a discriminator tap

One of the few devices I do not possess is a deviation meter and my TinySA is far too slow measuring deviation so after a little bit of searching online I found a project by an Australian ham for one that uses an FM receiver with a discriminator tap as the audio feed rather than through the normal audio chain.
So to this end I modified my TTI TCB550 with a discriminator tap from one of the ICs used in this radio, and this arrangement can be used without a mic being plugged into the radio.
the modification is incomplete as the tap is bare ended audio cable while I wait for a mono jack socket to fit to the radio to bring out the feed on a patch lead to the meter once the circuit is built, this is to allow a different receiver to be used for a different frequency however I will mainly use this with CB radios due to the age old myths amongst burner brigades and so-called "rig doctors" and "screwdriver experts" that turning FM deviation up makes you sound louder, better and helps you get out a bit further, in reality of course turning up FM deviation causes bleedover and causes you to sound distorted.
This video demonstrates the modification as it is but does not show it, the modification is using a 10k resistor off pin 9 of the SL5019 IC used in the receiver of the radio, soldering the resistor to the pin was tricky as it is a SOP16 package chip, the other side is a 10nF capacitor to ground and the wire of the audio cable to the resistor as well but before the capacitor, the braid went to ground.
Mostly a successful modification (and importantly legal as it makes no changes to the transmitter whatsoever as it is a receiver modification), I just need to add the socket on the outside of the radio to plug in a patch lead to the eventual device which will be built near enough imminently
#cbradio #hamradio #testequipment #electronics #diy #modification