Coax cable will have a certain amount of capacitance per ft. which if terminated to a high Z load in the speech equipment will result in a loss of high freq audio. If how ever the line is terminated with the characteristic Z of the line then it can be very long. This works ok for very low Z microphones but not for high Z mics. I build a transistor preamp with a low Z output such as an emitter follower into the microphone case and then run low Z cable to the speech equipment where it is terminated with a 50 ohm resistor. It is then XFMR coupled to the speech equipment circuit to prevent common mode hum induction. The XFMR coupling may not be necessary in all cases. A 600 ohm microphone (that is a microphone that is designed to work into a 600 ohm load as many studio mics are) will generally work well with 50 ohm coax and a 600 ohm termination provided the cable isn't a mile long.
John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Brett Gazdzinski Sent: Tuesday, January 13, 2004 7:14 AM To: [email protected] Subject: RE: [AMRadio] RE: r390a, sx17, t4xb for sale I made an interesting discovery Sunday. I have had a few reports of my audio not having a lot of highs, even though I boost the mid and upper voice frequencies. There is nothing to limit the highs in any of the rigs, other than the mod iron, and even crappy mod iron will typically pass high enough frequencies to sound good, and found the cord between the mike preamp and the power amp was the problem. It was a 15 foot piece of rg8m, the little coax, with phono ends on it. You would think something that works for RF service up into VHF would be able to pass high audio frequencies, but no. I wonder why it was so poor for audio, cutting stuff above about 3000 cycles a lot???? Brett N2DTS > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Brett Gazdzinski > Sent: Monday, January 12, 2004 11:13 AM > To: [email protected] > Subject: RE: [AMRadio] RE: r390a, sx17, t4xb for sale > > _______________________________________________ AMRadio mailing list [email protected] http://mailman.qth.net/mailman/listinfo/amradio
