Receive upgrade

I imagine the truck drivers would rather prefer information to misinformation.

"Those parts should have cost less then $2.00 with shipping, sounds like you like being took."

This implies he is being robbed. Most companies prefer to make a profit and stay in business rather than give things away and go out of business. If you order a hundred at a time then the price for the transistor or the Schottky diode is eight cents. For single quantities it is more like 55 cents each. This puts the total at around $2.75. This leaves a balance of $2.25 out of the $5, not bad for postage from Bangkok to the United States. They have to pay employees for the handling, packing, and mailing of the parts so no, I do not see how you can justify the comment he was being taken (i.e., robbed).

"Unless youi have lot's of experience with surface mount components and soldering - you probably need a hot air soldering gun to do the job right - you are better off leaving this modification to someone with a little more experience."

But they are NOT surface mount components so I guess he is going to be just fine.

"Unless one S Unit is the difference between hearing someone and not hearing someone - you won't be able to tell the difference."

You are saying there needs to be an S unit of difference to hear the signal. I would re-think this. I assume he is not watching the needle on the meter trying to figure out what the other station is saying.

"The one thing to remember is - when you make the receive more sensitive - you also make it more sensitive to static, lightning crashes and over power-being too close to the other people around you"

You are confusing several issues not only at once but also together. The hot carrier diode has a lower voltage drop as well as faster switching speed which in effect actually improves the performance of the receiver as far as these characteristics is concerned. The over power is a separate issue and has more to do with the dynamic range of the AGC circuit. I can tell you actual measurements show this is improved from around 80 to more like 120 DB. So no, none of these considerations become a problem doing this particular modification.

"The diode is in there to protect what ever is behind it and it is there to blow if something goes wrong."

The problem with this is you are in the wrong part of the circuit so this is a completely meaningless comment. The front end protect diodes are D1 and D2 in a Cobra 29. These are 1N4148's which are 50 ma silicon diodes. Absolutely nothing to do with the detector and noise blanking parts of the circuitry in the radio.

"Schottie Diodes has a lower forward Bias ( power consumption ) - hence if everything else is designed around the other diodes value - then the new value might mess something else up down the road."

The first part is confusing voltage with power and also assumes the diode is burning up the signal as heat (the power consumption part). This is not what they are doing in the circuit. While the second part has some basis I have done the comparisons of signal before and after as well as injecting noise using an IFR 1200 Super S and can tell you the receiver's performance (including dynamic range) is improved assuming the alignment at all points is being correctly done. You need to actually do a thing before making across the board statements of fact about a thing. Just common sense.


"Load it like a freight car, drive it like a stock car!"

I'm sorry, but professional drivers load their trucks properly within legal weight limits and drive safer and more professionally than anyone with only 4 wheeler driving experience. They drive as a profession not just for leisure so I cannot see how this signature is doing them justice. Rather I think it is most annoying to the real pro's out here since it supports a negative image I have no doubt most of them do not appreciate.

 

Somewhat disagree ......

I have moded radios using the 2SC2999 to replace the 2SC1674 and it results in about a 6 db gain in REAL sensitivity from about .7 to about .4 uv in many radios. So the transistor DOES work .... now the diodes I have found it varies from radio to radio .....

Still $5 is fair even if a bit high ..

 

When these radios were first designed the low cost FM 9 volt transistor radio was just arriving on the market and the 10.7 MHZ ceramic filter was being mass produced cheaply. You should look at the specs for this component it is a nightmare for a receiver such as we are talking about here. Being cheap as well the engineers decided to use this part for FL1 instead of spending the bucks to make a nice 6 KHZ wide 10.695 MHZ crystal filter. Sadly we are still stuck with the thing. How I wish that would have been corrected years ago. By now the mass production of said filter would have lowered the cost and we would all have CB's with a so much better receiver. This concept is what prompted Lou Franklin to come out with his crystal filter many years ago. How I wish He would have contracted some company in Japan all those years ago to properly construct a filter instead of using a couple crystals and transistor to cobble one together. This area is one where a real difference could have been made long ago.

Forgot to add earlier but my Mastercard was hot carded twice over 19 months ordering from Futurelec. My crappy bank charges $24 to reissue which you eat. I still have a hundred or so of all parts so unless these guys take a money order in the mail I am done with them. Any of you only needing a few parts for your own rigs, I suggest you pay the extra on fleabay or somewhere. In the end you still save money. I have to order hundreds so I will still buy from them, but I have not needed anything for months, nor for months more. I have not yet checked to see if they take other forms of payment. I most strongly urge you not to use your card in Thailand!

 

I have used many ch guards ( 455khz, 10.695 and 7.8 mhz ones in many projects invcluding home made receivers and they are VERY good.

ADDING them to what is already in the radio makes a world of diffrence a few ch away .....

But your right it would have been a killer part if it was 4 6 or 8 pole instead of 2 back to back with a preamp .....

 

Deerslayer1143,
Ok. I see the radio.
I installed this mod on my DX949, Cobra 29 LTD BT and a 29 Chrome. All good. . My radio(s) is much quieter. And reception is not compromised. The stock rf amp on my DX949 radio is of equal or better quality than the 2sc2999, so no replacement was necessary. And mod even before replacing the rf amp on the Cobras, made a huge difference in reception and lessened the noise lever.

Thanks for posting the mod.

Jimbo

 

What did you measure it with ?????????????

 

The reception before/after this mod. Real world situations.
I drive 60 hrs a week. I found this mod and performed it on 3 radios, for 3 different full time commercial drivers. All commented on how quiet their radio is, and the increase in reception.
From what I understood, the reasoning behind this upgrade is. To replace poor quality parts, that cause noise within themselves.
I did find replacing the amp made little difference. Replacing the diodes is what effected the noise and reception in each radio.
I'm no expert. I just repair radios. These are the first mod(s) I have done.
I converse with the radios I have repaired/modified everyday.
I also replaced jp36 w/cap and resistor. Which kicked their tx power up to 20 - 23
watts.
I guaranty my work with a full replacement radio if I cause the owner's radio to fail.

Jimbo

 

The diodes help with noise blanking that’s a given ....

Measuring the noise floor on the air CAN be done but it would be at best a iffy thing to do ....

I MEASURED the 2SC1674 / 2SC2999 change with both my Lambkin generator which is very old and the shop IFR-1220s and got about a 2:1 improvement in receiver sensitivity measured ....

 

My tech gets consistent results of -125db regardless of
The radio being tuned due to the sophistication of his test equipment. It sounds like everyone is spinning their wheels playing catch up.

 

Sensitivity means nothing when you have some idiot with a kilowatt driving down the road on another channel and you can't hear a thing, that's why export radios suck their selectivity on the front end is too broad.