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Maxgain
Member
Username: Maxgain
Post Number: 58
Registered: 3-2007
| | Posted on Tuesday, March 02, 2010 - 11:04 pm: | 
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I have an external modulation meter that I have used on my cb equipment for years. It is a rather inexpensive Midland brand in a steel cabinet that also reads watts and swr. The meter is good down to 3.5 mhz.
Over the years I have become acustomed to the way the meter reacts when showing A.M. modulation levels. CB's with "enhanced" transmit audio will always push the modulation meter's needle quickly into the red zone past the 100% mark. Even stock cb's move the meter quickly.
The key word here is "quickly". With every syllable of speech , the meter reacts instantaneously.
That's with CB radio's...
Now, when I connect an Icom or Yaesu or Kenwood to the SAME modulation meter , set them to A.M. and set the transmit power to the SAME level as the CB's, the modulation meter moves more slowly, sluggish in fact.
No, there is nothing wrong with the ham rigs.
Why is there this difference?
No matter where the mic gain is set on the ham rigs, the modulation meter definitly does not move quickly like when used on the cb equipment.
I have always wondered why there is this difference.
thanks |
Onelasttime
Junior Member
Username: Onelasttime
Post Number: 14
Registered: 8-2011
| | Posted on Thursday, August 11, 2011 - 2:10 am: |
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This is my best guess. I apprenticed for two years in an electronic repair shop that did tons of RF work for ham, CB'er's, the local government and radar gear for the airport and anything else that came along. When ever lesser RF technicians got stumped they sent their customer to the place I apprenticed for 2 years at.
So most of my experience is hands on not book work. In fact all the SMD devices started to really come strong and I decided to go to college for something all together different. SO I am not Tech at all and do not pretend to be.
Most amatuer gear I have worked on use's low level modulation in their audio section because AM is like the ugly red headed step child in Amatuer circles in America so it is not really that important of a mode. In most of those rigs the USB and CW circuits will be tight and near perfection with lots of notch filter's to chose from and voice processors rf clipping and all the other goodies. Most of those rigs also use mic's with wildly different impedance then what we would see in the CB world and even their keying circuits are totally different then what you would expect to see in a CB....So other then them both being two way radio's they have nothing at all in common especialy on AM! IT would be like comparing direct injection diesel engine to a port injection gasoline engine just because they are attached to a body with 4 tires on it and they roll down the road.
So I would guess it is the very common low level modulation on AM that most of them use. In fact if you have ever put a President Lincoln, HR2510, etc....you will be looking at a common freebander radio that use's low level modulation. Everyone that talks AM on these does one of three things.......Old M104/D104 mic, voice compression like SP1-a or something like it or they use a Ham base mic like one of MFJ's with speech processor built in. The best solution is some form of compression be it in the radio or in the mic. My Lincoln has an SP1-a as designed by Clear Channel and with that alone I get 1 more S unit on distant stations, always have loud clear audio and when on SSB where I spend most of my time I normaly punch through pile up's no problem.
Also a 300 watt RMS out put + SP1-a get's me the same effect as those running 600watt RMS AMP's. Not all speech comprossors act the some some of them also filter out the deep low freq.'s because they do nothing for how easy it is to understand your transmission. I have only used the SP1-a.
As for the speed of the needle that is a buffering issue. I am guessing their is no buffering or even magnetic damping on it at all so it moves freely. In this case no harm but if it got to moving too much it would not be readable. Their is always a compromise between how accurate a reading is and how readable the needle is and the person that designed it probably took that into account and biased towards accurate indication of what is going on. That is way some meter's really dance like crazy and some brands move much more slowly.
You can hear the difference by the way between the ham gear and CB gear. You just need to sample the signal. The amateur gear will normally have fantastic sound quality if not be being processed but it will sound weak on the recieve side of other radio's the CB signal will not sound as good or better yet as accurate as your voice sounds in real life but it will be much much louder on the receive side of other's. Have one of your friends record you on your various rigs so you hear the difference in your voice and ask them to rate the strength of your audio.
Hope that helps a little. In fact the only Amateur radio that is modern and built with SMD's that has good AM is the RCI-29XX-DX....I am guessing it
has the best AM audio of any modern Amateur radio on the market! |
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