FM Carrier / Deadkey

[zumlin]

Would the FM carrier of one of these radios be the deadkey.

I cannot lower my FM output it seems to be a solid 20W
AM is fully variable 0-10W DK.

If I was to drive an Amp using FM how would this relate to my Dead Key? 20W?

I can only locate discussion of AM and Swing, I understand FM has no swing but I assume I would still need to lower it to drive an amp using FM?

 

[Butcher318]

What radio do you have ? the FM carrier should be variable like on AM. Also, in FM mode when you talk there is no swing, it's all carrier the whole time. FM can really heat an amp up fast, I would try with a much lower carrier input.

 

[TonyV225]

depending on your radio like some radios AM is controlled by the external rf power control knob but SSB is only able to be set internally by the variable resistor. That may be the case with FM on your radio but Im not 100% positive I cant see why they do or would do that.

 

[zumlin]

Yea I figured it was too high for an amp its a Northpoint NT-4-HP, I cannot locate any way to adjust FM on the Net....I think they are stock with NPC modded finals 1969's or sumthin....after a second look at the output it seems to be almost 40Watts in FM like it goes max output, I have read other Ham gear does this also, just wanted to verify it was still considered dead key wattage.

I can adjust a VR13 for AM for sure. It has a 9821R20 board like a stryker but dual finals like a 77HML galaxy.....cant locate an exact match to this radio.

 

[TonyV225]

theres a vr that will adjust that internally whatever your AM is set at your FM can be set at as far as running an amp. its a good thing you caught that FM power being that high

 

[ken white]

Since the modulation occurs by changing the frequency, and not changing amplitude, the dead-key and modulated signal will contain the same power. You can probably adjust the transmitters power, but it should not change with modulation. As a side note, FM is allocated a lot more BW, so sending an FM signal to an amplifier designed for CB probably won't work very well.

 

[Captain Kilowatt]

As a side note, FM is allocated a lot more BW, so sending an FM signal to an amplifier designed for CB probably won't work very well.

Hunh :?: :shock: The transmitted bandwidth of an FM signal is wider than an AM signal but is still only about 10 KHz wide.There is NO reason an amp designed for CB will not work on FM.They are designed for at least 25-30 MHz and often more.

 

[ken white]

As a side note, FM is allocated a lot more BW, so sending an FM signal to an amplifier designed for CB probably won't work very well.

Hunh :?: :shock: The transmitted bandwidth of an FM signal is wider than an AM signal but is still only about 10 KHz wide.There is NO reason an amp designed for CB will not work on FM.They are designed for at least 25-30 MHz and often more.

Yeah, I should have said FM typically requires more BW. When using FM and a high modulation index, the frequency spread is quite wide and since the power is the same for all frequencies, there is a lot more energy generated at the ends of the channel allocated BW. All of my experience with FM is with signals in the VHF band and above so I should have probably researched the HF FM band a little before opening my mouth.



What are the HF FM band specifications?

Also, that is a pretty wide non selectable BW amplifier even for the amature bands. I did't know amplifiers were allowed to be designed for CB's? I thought CB's were limited in the US to 4W. I guess Canada allows more power?

:?

 

[Captain Kilowatt]

Hi Ken. No we have the same power limits on CB as you guys do and amps for CB's are not legal in either country but a lot of folks use them.Most of those amps do not have much for tuned inputs or outputs except wideband toroid transformers.Often they will work as low as 40m and then some.I say "work" as in will provide more out than in but how well they "work" down there is quite debatable.

Here in Canada hams do not have any mode restrictions on the HF bands.We just have to abide by bandwidth restrictions. I can legally run narrow band FM with +/- 2.5 KHz deviation on 3.510 MHz if I want too. I can't for the life of me think WHY I would but I can if I wanted to. :? AFAIK in the US, FM on HF is restricted to 29.000-29.700 MHz.Some please correct me if I am wrong.I do not keep a copy of FCC part 97 handy.

 

[ss8541]

am's bandwidth is 6khz.

nnbfm (narrow narrow band fm) bandwidth is 11khz.
this for a max. audio freq. of 3khz and max. deviation of +/-2.5khz

wnbfm (wide narrow band fm) bandwidth is 16khz.
this for a max. audio freq. of 3khz and max. deviation of +/-5khz.

wbfm (wide band fm; broadcast band) bandwidth is 180khz.
this for a max. audio freq. of 15khz and max. deviation of +/-75khz.

the only fm signal that may not work well with a cb type amplifier would be wbfm since it is 180khz wide. that is almost 1/2 as wide as the entire 40ch citizen band. i'm -ass-uming here that this is the band ken is/was referring to.

then again, there are guys who bleed all over the entire 40ch band...seems like their amps handle the wide bandwidth -VERY- well.

 

[TonyV225]

I have personally never seen an amplifier export style that didnt work on FM ive seen them used FM quite a few times. As a matter of fact the ones with the mode switches to set the relays for SSB say AM-FM and then the bottom or down position of the rocker switch says SSB.

 

[ss8541]

for those of you who may give a flying $%^, there is a formula to determine the bandwidth of an fm signal. it is called 'carson's rule'.

you need to know the maximum audio frequency and the maximum deviation. the equation is;

fm bandwidth = 2(maximum audio freq. + maximum deviation)

example;

nbfm bandwidth = 2(3khz +5khz)
nbfm bandwidth = 2(8khz)
nbfm bandwidth = 16khz

your local fire, police, etc is most likey nbfm. they have a 25khz channel spacing but only occupy the 16khz listed above. by 2013 they'll all have to be nnbfm and fit into half the space (12.5khz). this will be the new fcc 'refarming'. can't wait...$$$$$..

 

[Captain Kilowatt]

That's true Richard. I should have said with a bandwidth limit of +/- 2.5 KHz not deviation as the allowable bandwidth limit is 6 KHz.I have heard of a couple guys playing around with such modulation schemes but I can't figure out why.

BTW since you are in the business you are,would you happen to know where I can get a manual for a Wavetek 4101 AM/FM modulation meter? I have one in like new condx but I am lacking a manual.No big deal but I do have a few questions that I am sure would be answered in the manual.

 

[ss8541]

6khz bandwidth for fm. man, no analog there, you could only use digital modulation like c4fm/4 level fsk.

as for the manual, you may try ridge equipment they have a ton of manuals. i'd give them a call.

 

[ken white]

am's bandwidth is 6khz.

nnbfm (narrow narrow band fm) bandwidth is 11khz.
this for a max. audio freq. of 3khz and max. deviation of +/-2.5khz

wnbfm (wide narrow band fm) bandwidth is 16khz.
this for a max. audio freq. of 3khz and max. deviation of +/-5khz.

wbfm (wide band fm; broadcast band) bandwidth is 180khz.
this for a max. audio freq. of 15khz and max. deviation of +/-75khz.

the only fm signal that may not work well with a cb type amplifier would be wbfm since it is 180khz wide. that is almost 1/2 as wide as the entire 40ch citizen band. i'm -ass-uming here that this is the band ken is/was referring to.

then again, there are guys who bleed all over the entire 40ch band...seems like their amps handle the wide bandwidth -VERY- well.

ss8541, I was just making a general statement and thanks for posting the specifications.

Ken