K5LAD - 50+ Years of Ham Radio Memories

Volume XX

Eh????   What Did You Say???

Have you ever wondered why crystal microphones are not used in a mobile?  Actually, there are several reasons, depending on what period of time you’re wondering about.  Now a days, almost every microphone, both mobile and home station, are either dynamic or electret.  Dynamic elements are like miniature speakers with a diaphragm attached to a coil of wire surrounding a magnet and electret require application of a low voltage (typically less than 10 volts) to power them up.  Most current radios use low impedance (low Z) microphones because they’re used with radios that use transistors and integrated circuits that are, by design, low impedance devices.  During my earlier hamming days, back in the 1950s and 60s, most radios were tube type and were high impedance (hi Z) input for microphones.

Mobilers also often used an available crystal mike and discovered that they sounded good and worked well when they were first hooked up.  If the ham first started using this accessory during the wintertime, he might have had quite a bit of success with it for days, weeks, and maybe even months.  Then the strangest thing happened – as springtime came and days because longer and warmer, it was not uncommon for the ham to come out to his mobile after putting in a hard day and nobody seemed to want to talk to him.  Tulsa hams had a common mobile frequency (3825 kc) where all the locals gathered, particularly when they were mobile.  Every mobile operator in the Tulsa area owned a 3825 kc. crystal.  Remember this was 10 to 15 years before hams discovered the old Motorola and GE police, fire, and taxicab FM transceivers.  Repeaters were still a few years off and the “place to be” in the Tulsa area as a mobile operator was 3825 kc. 

 But, back to that mobile…………….. “Why won’t anyone answer my call?  And when there was a QSO on frequency, and I give him a call, why won’t he come back?  You ‘spose he’s just being ornery and ignoring me?”

 Actually what happened was, the crystal elements used in microphones were susceptible to being destroyed by heat and, to some extent, by excessive cold temperatures.  The problem usually reared its ugly head after the temperature inside the vehicle had reached the high temperatures we, here in Oklahoma, are familiar seeing when the car is closed up for several hours in warm weather.  The elevated temperatures would destroy the crystal microphone element.

 When I say destroy, that’s not exactly the truth.  The element would still vibrate and generate sounds but with no intelligence conveyed on the transmitter signal. (That previous comment lends itself so well to some really good comments on so many other ham transmissions that also had no intelligence conveyed but that’s not what this article is about.  Perhaps another day………)  When the user of a heat-destroyed crystal mike tried to use it you could almost tell that someone was talking because you could hear a sound going up and down with their speech.  I can imitate the sound in person but that’s a little difficult to share via this medium so I’ll only say, if you place your tongue on the roof of your mouth and speak a sentence by making whatever sounds you can (awkward because to the tongue location) but still move your lips to the words in the sentence, just as though you were still talking, that’s roughly what it sounded like.  It’s a little like the cartoon version of Charlie Brown talking to his teacher but with not quite as much “wa – wa” sounds as you heard from his teacher.

 Just imagine being on the receiving end of a transmission like that.  Once the crystal element had gone through only one Oklahoma spring or summer DAY, it was useless forever more. 

 Not only did this problem show up in Tulsa and in Oklahoma but with mobile operators all over the country.  Microphone manufacturers quickly realized, when they started getting all the complaints, that they needed an alternate solution for a high impedance mobile microphone.  This was met with the ceramic microphone.  The ceramic cartridge sounded almost as good as the crystal element and it was not damaged by heat.  Most manufacturers of microphone elements offered any of their hi Z elements in either crystal or ceramic versions.  The crystal elements were usually used in the home station and the ceramic element in the mobile.

 Mentioning mobile microphone in those earlier days would not be complete if I didn’t also mention the carbon microphones.  Some mobile transmitters, particularly the home brewed models, used carbon elements.  The low Z carbon elements required less amplification than the hi Z models so it would often let the builder have at least one or more fewer tubes in the modulator section.  Carbon elements sounded remarkably good and were also popular. 

 There were two main sources for carbon elements:  the military surplus T-17, which you often see in old WWII movies.  Especially when the bomber pilot talked on a microphone, he was using a T-17.  The T-17 microphone cord was a straight piece since this was before the day of the “curly cord.”  The interesting thing about the T-17 was the powerful spring used in the PTT switch.   It was so terribly strong that few people could make much over a 1 minute transmission before their thumb muscles gave out.    This provided an automatic transmission limiter, whether they intended that or not.

The other carbon element “available” to the general public, and many hams in general, was in the microphone handset of a Western Electric telephone.  This source, by coincidence, seemed almost inexhaustible.  I’m not sure if the statute of limitations has expired so I dare not say any more. 

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