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Deadkey vs swing

loosecannon said:
the truth is, you just cant really trust most wattmeters to be accurate.

try this, assuming the limiter diode in that 25 has not been clipped; turn the modulation pot down until you see a 1 watt deadkey swinging to about 4 or 5 watts on your dosy.
the mic gain on the front of the radio should be all the way up.
make sure that you have put the trap coils back the way they were before you do this.

now try it with the amp.
what does the amp put out now?
LC
Click to expand...

I never (or anyone) touched the traps on this rig.. The limiter is is place, and mod is all the way up.. There is a cap/resistor lowering the deadkey. if 1/4 is ideal, then its fine the way it is for an amp.. Correct so far? if 50 - 200 is ideal, then where should it be using it by itself without an amp
 
for the radio output 1/2w swinging to 2w, or 1 watt swinging to 4 watts. use the watt meter before the amp to check this. your cobra 25 will not put out 20w with the stock final. mabey 9 at best if you were to measure true output. if your lookin for more power you should change the driver to a 2sc2314 and the final to a 2sc1969, and get rid of that junky swing kit. look at the schematic or another 25 and put it back to stock before doing anything else so when you run into problems we can help. be warned good 1969's are hard to find as there are plenty of junk imports right now that will hardly do the 12w they are supposed to do stock. if done right 18w could be seen.

you could always do the erf2030 mosfet swap but again that tends to make your dead key very low and output power usually isnt very linier.

http://www.worldwidedx.com/radio-ra...watt-erf2030-mod-cobra-25-uniden-66-68-a.html

the reason for 1 watt or less input into the amp is so that you dont overdive it into saturation or dammage the amp. you need to limit your peak output for the same reasons as well as limit harmonic's. your swing kit (diode, cap) is only hurting you right now and will not allow proper setup with it.

to awnser your question on 4 watts in 150 watts out its apples and oranges. they are measuring the radios output compared to the amps output. the radios dead key and peak wattage should be compared and the amps deadkey and peak wattage should be compared. a 1w key into the amp may make 35w-40w amp deadkey. 4 watt radio peak would make 150-160 amp peak. think of it as 40w swinging 160w, not 4w swinging 160w.
 
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your Tstar 250 is not a 250 watt amp . it uses a pair of 2-sc2290 pills/transistors and they are rated for 60 watts pep @ 28 MHz. . yes thats at 12.5 volts and yes you can get a little more with the 14.4 volts vehicles provide when they are running . id run it to no more than 150 pep if it were me , it will be cleaner , run cooler and last longer . its not like the 100 watt difference will make a real difference in your signal strength or talking distance .
 
Carl said:
for the radio output 1/2w swinging to 2w, or 1 watt swinging to 4 watts. use the watt meter before the amp to check this. your cobra 25 will not put out 20w with the stock final. mabey 9 at best if you were to measure true output. if your lookin for more power you should change the driver to a 2sc2314 and the final to a 2sc1969, and get rid of that junky swing kit. look at the schematic or another 25 and put it back to stock before doing anything else so when you run into problems we can help. be warned good 1969's are hard to find as there are plenty of junk imports right now that will hardly do the 12w they are supposed to do stock. if done right 18w could be seen.

you could always do the erf2030 mosfet swap but again that tends to make your dead key very low and output power usually isnt very linier.

http://www.worldwidedx.com/radio-ra...watt-erf2030-mod-cobra-25-uniden-66-68-a.html

the reason for 1 watt or less input into the amp is so that you dont overdive it into saturation or dammage the amp. you need to limit your peak output for the same reasons as well as limit harmonic's. your swing kit (diode, cap) is only hurting you right now and will not allow proper setup with it.

to awnser your question on 4 watts in 150 watts out its apples and oranges. they are measuring the radios output compared to the amps output. the radios dead key and peak wattage should be compared and the amps deadkey and peak wattage should be compared. a 1w key into the amp may make 35w-40w amp deadkey. 4 watt radio peak would make 150-160 amp peak. think of it as 40w swinging 160w, not 4w swinging 160w.
Click to expand...


Thanx.. Thats not what I said though... i said barefoot the radio is doing a little under 1w and swings to around 10.. With the amp its seen as 50W swinging to 200w.. I know its stated the amp cant do 250.. but thats what the dosy says at 14v. So whats the point of peek and tune is all you want to swing to is 4w? So your saying 1w carrier to 4w swing would beat the setup with the swing kit? I would think 50W DK and swinging upwards near the amps peek would be perfect.. Just wanted to know where it should be barefoot
 
peaking only applied for max output, when running barefoot you look for max output. as you have learned when driving an amp you need to tune the radio for the amp's requirements not maximum output. perhaps of you were driving some 3-500z tubes or 2sc2879 transistors that could handle more wattage.
i took the liberty of finding the data sheet for the transistors in your amp if you like you can read it and find the spec's for your input power. in case you don't want to its listed at typical drive of 2.5w, maximum drive will be 4w. they don't need very much as far as drive goes to produce proper and more importantly clean output.

if it were me i would try for 1/2 watt swinging 2 watts, you cannot obtain this with a swing kit installed. swing kits do nothing more than distort your modulation and make the meter on the other end dance. it has absolutely no positive effects on your transmission. you will lose every time to a signal with more carrier. to much carrier will leave your signal under modulated, to little carrier will leave you over modulated.

dosy meters tend to read 30% to 40% over pep depending on the amount of wattage there is. the higher the drive the higher they will error. a more accurate meter would be a coaxial dynamics or a used bird meter (new china made ones don't seem to be as good as the older usa units). for the ultimate in accuracy you would need a rf demodulator and a oscilloscope.
 
I think the swing kit has some legitimate uses especially when it's equipped with a variable carrier. Simbalage is a classic example. When you have two different drive requirements. One for barefoot that allows approximately full radio output and one with reduced carrier to drive the pair of 2SC2290's. It is a fact that the swing kit can cause distortion. Set the carrier too low and you'll hit RF cutoff on negative peaks. Set it too high and you'll clip all the positive peaks off.

When keying against another AM signal that may have more carrier then you, your carrier only affects what is heard between your words. The lower carrier may allow the other station to get through when you are not modulating but as soon as the carrier is modulated your output is increased way beyond the carrier level. Your chances of being heard over the station with a higher carrier are actually best when you have no carrier at all.

If you go to SSB and tune the other AM station in and then key with them on SSB, you are much more likely to be heard. This demonstrates how much more efficient SSB is once you remove the carrier and one sideband. You have effectively hijacked the other stations carrier and used it to demodulate your SSB signal in other AM receivers.

Dosy meters tend to read 30 to 40 % below actual PEP levels because the meter is not active. Meaning it uses the RF to deflect the meter rather then a separate power source. Without the separate power source the capacitor in the meter that is suppose to charge to the peak of the applied voltage never gets the time to reach this point due to the short duration of the peaks.
 
Carl, if you are talking about average readings on the Dosy then I agree with them being inflated. It looked like your post said they read 30 to 40% over PEP. In this case that would not be accurate for the reasons explained regarding the capacitor in the PEP meter.
 
over actual pep, my bone stock 76ltw untuned on a dosy says 12w. they are very optimistic.
 
The stock 4 watt radio should still only show 4 watts average when fully modulated. Of course the Dosy will read higher here. That same 4 watt fully modulated average reading should occur while simultaneously showing 16 watts real PEP. That's where the Dosy falls short on PEP and will read less.
 
WOW! Thanks so much, Someone finally cought on to the question (2 different driving requirements) why didnt I think to word it like that LOL.. So if I am correct, if the swing kit is lowering the carrier and doesnt sound bad I could leave it for when using the amp.. And bypass for barefoot to raise the carrier a tad? Because likewise doing 1/4 of power for carrier like someone said, with the amp ppl say its awsome.. good swing, clear ect.. ect.. but barefoot is where I run into a problem because is less then 1w swinging to around 10.. but on the amp is 5o swinging forward.. has anyone actually paid attention when power is applied? seems you loose your swing.. my base for some reason (No swingkit) sounds better on low then high.. High that does 100w swing forward with the amp.. So I go variable and its like 10w swinging forward. So thats the big delemma.. This cobra 25 with the infamous swing kit is getting better responses then the base
 
Simbalage22 said:
Thanx.. Thats not what I said though... i said barefoot the radio is doing a little under 1w and swings to around 10.. With the amp its seen as 50W swinging to 200w.. I know its stated the amp cant do 250.. but thats what the dosy says at 14v. So whats the point of peek and tune is all you want to swing to is 4w? So your saying 1w carrier to 4w swing would beat the setup with the swing kit? I would think 50W DK and swinging upwards near the amps peek would be perfect.. Just wanted to know where it should be barefoot
Click to expand...
do not change a thing or you will be disappointed,do not unmod it do not put mosfets in it.you stated you get reports that your clear.that amp should do between 180-250 watts average power you should be close to target.toshiba transistors are underrated and 2290 are closer to 80-90 watts give or take depending on input and voltage supplied.it sounds like its doing a good job as is.
 

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