Mosfet upgrade? Worth doing or waste of money?

[Captain Kilowatt]

I say analog is more reliable from my experiences in both personal use and at work now. When you had low signal strength, With analog, The message could still be communicated. Digital, If you don't meet a certain threshold of data content, forget it. Seen it last night actually.
I work with local PD and use the same radio they do. A unit keyed up right beside me, got the 3 chirps, asked for case number. I never heard any of it on mine. Neither did dispatch. He had to keep trying over and over before it went.... And these are public safety radios that peoples lives depend on and have to work no matter what instantly....? Yep. Ever tried to watch digital TV now days and its raining outside? Bunches of fun. Wait until the wind blows, Even better.... Yep, Digital is so much better alright... Rant over, Lol.
What is the formula for calculating db gain in so many increments? And where can I find radiation takeoff angle diagrams for say 1/2 wave, 5/8, etc...?

Digital is actually more reliable than analog given the same power output and frequency. The problem people have is they are used to a gradual degradation of signal rather than all or nothing. Digital will actually allow signal recovery with good clarity down to the point where analog would have become unintelligible. Television has shifted to UHF frequencies and actually runs much less power than the old analog transmitters did and that is part of the reason of reduced coverage in a lot of areas while in some areas that lower power has allowed crystal clear pictures when they used to have grainy reception. Hams have been using digital communication modes for years with low power and it has actually become the mode of choice for bouncing a signal off the moon. A station can run a single long boom antenna and 150 watts and be VERY reliable instead of the 1500 watts and four, eight or sixteen stacked antennas that used to be required on analog modes.

dB calculation formula is: dB= 10x log of the (power out divided by the power in) so brush on your logarithmic functions.

http://www.radio-electronics.com/info/formulae/decibels/decibel-formulae-equation.php

 

[SMILEX2692002]

I have had 2 Ranger 2995DXCF's blow out there Mosfets in the amplifier section.
Ranger fixed them both times under warranty.
I believe this radio cannot handle anything more than a 2.0 SWR.
I believe these mosfets cannot handle muchrmuch Watts coming back at them.
First time I made the mistake of leaving a 10 meter yagi inline and went to the 12 meter band and started calling CQ.
Very much a mismatched antenna.
The radio instantaneously shut off.
In both instances once the radios shut off they will not turn back on.
I believe the radios circuit board is powered last and the amplifier is powered first.
Since the amplifier is shorted out it will not allow power to travel past it to turn on the radio.
It's just my guess because this happened in both instances.
I sure do miss my Ranger 2995dx of the old days that had the two 2290's.
I believe that model would have handled this mistake.
Now I am extra careful with the one I have left.
I keep my bird 43 10 watt plug in reverse.
This way I will tell immediately if there is a presence of high SWR (Reflection coming back in)
it would be nice if Ranger installed some kind of SWR protection like most modern radio have now.

 

[Tallman]

I would do the mosfet mod if none of the proper transistors were available.
If you want power hang a quality amplifier behind your radio.

 

[guitar_199]

I was digging around for material on this subject and ran into your comment here.

When you do a MOSFET mod like that.... is it possible to NOT TUNE it for high power?

What I am getting at is..... if one's only reason for doing this is to replace old bipolar transistors that you can't get readily any more..... and you have moderate expectations for output.... CAN you tune it down to something reasonable so that the rest of the radio can tolerate it?

THanks!!!!
Bob

That doubling of power might.....I say MIGHT result in your signal increasing by one half an S-unit on the other end. It will also strain other components in theradio and power supply and generate more heat while doing it. The heatsink is already barely adequate for stock power.

 

[Handy Andy]

The "go-to" has been the IRF-520 - but now there are so-o-o-o many knockoffs - you'd be lucky to find one durable and actually rated for what the Datasheet says.

In the CB tricks days, you could use the "ERF" companion part and get by with the values used.- now you have to muddle thru what the radios' parts that it has still inside and perhaps the "mod sheet" works for most.

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Most people wanted that "40-watt" mod - and depending on which meter you used - you could fool some of the people some of the time and tell the rest...(never mind...)

So when faced with the inevitable - how to do a down and dirty quickie upgrade requires 1 - 1N4148, a 470 ohm and a 3.3K resistor to replace R56 with this part oriented like this and installed...

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You change "drive level" by changing value of C62.

For best results - "C390" doesn't exist on the TOP of the board, you install it ACROSS R56's new parts as a Drive "shunt" on the FOIL side to adjust and clean up the signal arriving to the MOSFET - it is done with JP36 INSTALLED to obtain your wattage figure of merit then you install a variable or what ever you wish at JP-36 to complete the "tune"

 

[Shadetree Mechanic]