My newbie setup... Cobra 29LX & Wilson Antenna

I guess I find it hard to believe that pep swing is insignificant in the overall performance of the radio, then how come articles state time and time again that carrier to pep should be set at a 1:4 ratio to acheive 100% modulation, if this is not true then who or what perpetuated this false rumour , and why are radios advertised time and time again, how many watts they will swing to but little mention of the carrier watts, just wondering.

 

I went to AM - TUTORIAL
Cbtricks.com
Read a good 4 part article on power, what it means, how it is measured, and the pros and cons of overmodulation, good information for all to see.

 

Question for N Ur Dreams, why did you advise not using a power mic? I have used both an Astatic D 104 and RF Limited Extreme 2018 echo mic on both my cobra 29 lx and bearcat 980 and the results are good, both radios are stock except I turned up amc in the cobra, and the addition of a power mic just gives the modulation a little kick. On the cobra I set the mic gain at 3:00, and on the 980 set mic gain at 3 and have the modulation control on both mics at a quarter. I was just curious why you are against them.

 

I read the AM article you cited again, read it when it was first posted but don't remember when.

When you are talking about swing on a meter, it is deceiving to say the least. Like SWR meters, there are watt meters and then there are 'wat' meters. I can't see many of them accurate unless it is like a lab meter, which I have. My birds are not all that accurate and used to measure average carrier power, but I depend on something that no one ever talks about, an RF current meter.

The article is a good attempt to explain what's going on but leaves out the way the input to the final amp is modulated, the relationship of that form of modulation to the carrier and the truth that the carrier is not measured accurately unless it is done on a lab quality instrument - it mentions that at the end of the article.

The four to one ration isn't about output when you come down to it, yes the article talks about it, but read it carefully and you can see what it means while it leaves out a few key things about that ratio. In fact there is a formula based on the efficiency of the amp and as I said the form of modulation which there are many of them. It is more or less a 1.5 to one ratio based on the average carrier without the peak reading meter or scope and as many may not understand this isn't measured by a watt meter as mentioned in the article.

I have many boat anchors, and broadcast transmitting gear here. I have a bunch of carrier controlled AM rigs like DX-60, T-60 and the Hallicrafters version. ALL of the controlled carrier ones have a swing to it but is inefficient in how they operate. The others like my gates transmitter and my T368 all do not have that. The first group sounds ok on the air, swinging every time I speak, but the latter sound great, no issue with swing but a solid carrier.

Which one would I rather have?

Of course the one that sounds good on the air.

I also have a couple class E transmitters which for the most part don't move much on the meter.

With that swing, there are other issues with carrier quality that the article you cited mentioned and that you can't measure, mainly poor modulation introduces harmonics and sidebands into the carrier that doesn't get filtered out - also mentioned in the article. One reason why "techs" (most of them) haven't got a *********** clue how to property tune a radio, even with a scope, they tune it without understanding what should be what.

Distortion is introduced long before the audio final amp, overdriving the mic amp is one problem the other is having a audio final amp that is limited to say three watts of power and driving it to produce ten by removing the limiter circuits, this in itself produces more harmonics that are propagated into the rf final amp section and add to the already improperly tuned amp section.

What results is a crappy sounding radio that people think sounds good. It is like the myth that the export/10 meter radios are better when they are in fact junk.

However one mistake made with these mistuned radios (other than the design has not really changed in 40 years) is the fact with that swing and that dirt producing carrier, the amps that are put behind them fail miserably in actually amplifying the signal properly. ALL of these amps today are based on one design and only one, FET or bi-polar, they are copied. That person who designed the design knew overdriving them or making them amplify dirty signals would produce non-linear signals at the other end. One reason why you don't see amateurs using CB amps.

SO my solution for all of this is to get it properly tuned, with the right mic (even stock mics can work well) and have a good amp if you are inclined to run an amp. The antenna system is far more important to focus on, with even the crappiest looking radio out there, if it is tuned right, it would sound good and get out with the right antenna system.

What is puzzling is I have a TR-452 40 channel radio shack beater that sounds great, it has great receive too. I put it against the Galaxys and the other high end radios I have and it still beats the crap out of them in sound quality. What I did to it was just replace the front end components a bit to tighten the receive up and tuned it right - nothing else. I have a couple others which are extensively modified and made to sound even better but for those that's all in the audio section, not in the RF section. Makes you wonder why people spend so much money on new junk when an older radio works just as well.

 

I appreciate your feedback can you direct me to some other informative articles I will find interesting.

 

I bought a Stryker 955 and love it, but I have been buying old radios lately. The 19 LTD, more recently a Grant XL, and most recently, a PC122. The Grant is in dire need of TLC, it was tuned by your typical hack shop. The PC122 isn't in my possession yet, but is supposed to be bone stock.

 

I have a Galaxy 99v2 that I bought a little over a year ago, paid 275.00 brand new converted, I see where the price has gone up. Overall its not bad good tx and rx but not worth the money, if you look at the board it looks cheap like a 949 board, alot plastic pots not the metal type that you see in a connex. A friend of mine bought one at same time and had problems with the voltage regulater in the first month of ownership. I just keep in my pickup truck running barefoot it does good for local communication.

 

Arrl Handbook is a start.

There is so much out there for the number of years that AM has been used - something like 100 plus.

The BBC actually has a very good book that was published in 1945 or so which really gives a lot of details and math, I have a copy of the actual book but was told there is a PDF out there in this internet thingy - haven't looked.

Also thinking about it, sites like AMFone and other AM sites have some good stuff out there, then you have Mauldroppers and their Hi-Fi stuff.

The list goes on.

I think that there is a lot of want to have the best without understanding what the best it. I put up my stoner or CPI as top end radios for SSB and others for AM.

I had a 955 I took in trade, had great anticipation over it but got the owner's manual out and was disappointed with 11 pages of superficial crap. My newly acquired TS-2000 Kenwood radio has a 150 page manual, which I know makes sense to a point but with a good radio, I expected more than 11 pages. Big deal it has different colors or it can be "programmed" - that is meaningless when you can't have a good level of quality built in and proven by actually working better than the cheaper ones. I traded it for something I don't need but didn't want to pass up, FT-301zd.

I've been on a buying spree for old CBs, most are coming out of estate sales (like the TR-458 I got for $15), don't laugh at this but I've been buying a bunch of old Johnson radios, looking for 323A which in my opinion is a very good radio design. It has better receive than most and especially today's radios - especially exports and 10 meter rigs.

I've got a couple cobra 2000s that need work, I can't believe the hack jobs. someone put in a echo board and screwed it all up. I can't find a thing about this version of echo so I will have to do a scratch repair - meaning figuring it out via the schematic.

 

if you bleeding all the way up to 2.4ghz and beyond you have a problem