which mic. is the best...

[ddbddg1]

I just got a new dx-959 (well, new to me) and it came with the stock galaxy mic. radio and mic. are practically new.
I have 3 other mics also
a cobra m73sL
a astatic 636L
a old astatic d104 lollipop
and i am wondering about which mic. to use with it.....which is the best....the stock galaxy or one of the others?
any advice is appreciated....thanks

[zodiac]

Forget the standard mike, use the lollipop.

[mrmodulation]

I will agree with Zodiac,
The audio bandwith of most CB radios is 300hz - 3Khz, the D104 has a very peaky midrange (1Khz) This is the centerband of your voice and contains the most POWER! There were several different "heads" made for different applications and they all sound different in there own way.

The trick to getting the best possible sound out of any radio is to "match" a microphone to it, There are several things that need to be met to get it right:

1. The mic MUST have the same impedance (resistance) as the radios mic input (600 ohm - 1Kohm)

2. The bandwidth of the mike MUST be the same as the radio

3. The output level of the mic MUST be set to the same output level as the origional radio mic

There is a HUGE misconseption going around that if you connect a microphone with big bass to an SSB radio you will get "Big Bass"
This is totally untrue all the microphone circuits eg: pre amp, ballanced modulator and SSB filter are designed for a specific bandwidth under FCC design rules and most of the lower bass frequencies will not pass through the radio and will cause overload and even damage to these circuits.

Clinton TRA-087

[lbcomms]

The mic MUST have the same impedance (resistance) as the radios mic input (600 ohm - 1Kohm)

With RF (sch as the antenna circuit) that's true, but it's a bit different for audio.
With audio, the source (mic) needs to have a much lower impedance than the load (radio).

Most mics are in the 50 to 750 ohm range, most radios are in the 5K to 10K range, so it usually works out OK.
Occasionally, you would get someone put a cheapie power mic on a radio with a lower impedance (such as the Cobra 148 or Uniden Grant) and wonder why the audio was so "tinny".

The ratio of output:input impedance is known as "damping factor" (google it and read the Wiki page if you have never heard of this term or you are not sure what it means).
A damping factor of less than 10 will result in frequency response shifts, and as you go towards a value of one, possibly oscillations and "ringing".

Damping factor is a figure usually used for audio power amps driving a speaker, but it applies equally when putting 2 amplifiers (i.e. the power mic and the radio) in series.

The bandwidth of the mike MUST be the same as the radio

Nearly all mikes will have a response far greater than the radio - connect one to a CRO, use an audio generator to make some out-of-band tones such as 100Hz and 5Khz, and look at the pretty sine waves on the screen
Some Densi base mics have a response from 40Hz to 15Khz (hi-fi!).
This is actually a not an issue, all radios have a bandpass filter to only let through the voice (300-3000Hz) frequencies. The other frequencies picked up by the microphone will be discarded by the radio.

The output level of the mic MUST be set to the same output level as the origional radio mic

You can actually go quite a bit higher - there is a limiter in the radio that will reduce the gain to compensate.
Doing this raises the average signal level, which is useful for communicating with weak / DX stations.
Not so good sounding for the locals - that's what the gain adjustment / mic gain control is for...

Most limiters have a 30dB compression range - that's a 1000 to 1 range.
Even if your new mic has TEN times the output of the old one, you are still only using 1% of the available reduction of the limiter circuit.

most of the lower bass frequencies will not pass through the radio and will cause overload and even damage to these circuits

If they "do not pass through" how can they cause damage?

To go past the limiter capabilities of a typical radio, you'd need to go 1000 tines (30dB) past it's limit. Not likely in practice.
A typical mic can typically put out 25mV - this would need 25 volts of audio to hit the limit - no mic amp would put out anywhere near 25V.

Of course, it you have done noob tricks such as disabling the limiter or putting in a so-called "swing kit" then part 3 does not apply

Sue

[broken580]

ch - lower the noise threshold allowing only the strongest, hopefully clearest, signals through the speaker.
3. RF Gain - limits the receiver's ability to receive more distant signals permitting only stronger nearby signals to be received.
4. Clarifier - on radios equipped with single sideband capability it is used to permit reception/transmission of signals at the same point on the frequency as the station with which you are trying to communicate.

[9Lives]

I just got the rci sra-198 love it! Did the cap/resistor mod for

[lordkevin]

ch - lower the noise threshold allowing only the strongest, hopefully clearest, signals through the speaker.
3. RF Gain - limits the receiver's ability to receive more distant signals permitting only stronger nearby signals to be received.
4. Clarifier - on radios equipped with single sideband capability it is used to permit reception/transmission of signals at the same point on the frequency as the station with which you are trying to communicate.