Does QRP AM make any sense?

[flintstone mop]

OK Gary,
maybe the Retro 75 has better modulation characteristics than other rigs running in this QRP class. And the antenna and location of the operator might dictate if QRP will be a fun thing or struggle.
Other replies seem to be hinting that many folks are not monitoring their modulation. And are transmitting square waves or 20% pos.peaks

fred

[kb3ouk]

25-30 watts can be useable on 160 depending on the following  conditions: time of day, season, and how good your antenna is. this winter i was running 25 watts on 160 into a 250 or so feet of wire that i couldn't get lower than a 3:1 swr, in the early evening (around 5 or 6, not quite dark yet) and was be heard about 100-200 miles away.

[flintstone mop]

25-30 watts can be useable on 160 depending on the following  conditions: time of day, season, and how good your antenna is. this winter i was running 25 watts on 160 into a 250 or so feet of wire that i couldn't get lower than a 3:1 swr, in the early evening (around 5 or 6, not quite dark yet) and was be heard about 100-200 miles away.

Very good points

[kg8lb]

 We put together a PLL rig that runs 1 watt from 1.5 to 2.0 MHZ.Very Hi-Fi freq response , even has stereo capability.  Loaded it in to a  random wire on 1.885 a few years ago and had good results with K8TV in Cleveland. Wouldn't call it a primary station but it worked well at 200+ miles early evening on 160. It works very well on ground wave for local contacts.
  Of course QRP operation is subject to the prevailing conditions but the potential is real .Personal preferences aside, operation is far more satisfactory than many people who have never tried it may realize.

  QRP CW is purely amazing on just about any HF band . The operators on CW are generally quite adept at working QRP.

[WD5JKO]

Last night on 75m around 8 pm central the band went long very suddenly. Between poor propagation, and local high noise levels, it seemed everybody was running QRP! Actually running real QRP in the late afternoon/early evening is much more rewarding than running legal limit when the band goes long..

Jim
WD5JKO

[KM1H]

In the days of old when knights were bold and all that crap 10-30W output of mobile AM had no problem with 10-30 miles of coverage to a home station with a 20' high dipole. About 3-10 miles mobile to mobile. Figure about 4% efficiency with a real good 8' whip and center loading.

Ignition noise was the killer. If I ran push on spark plug resistors the souped up V8 flathead would stutter at anything over about 2500 rpm. There were no resistor plugs, wires, and SS ignitions in the 50's. This was with a Mallory dual point distributor. The TX was a TBS-50D and a Gonset converter into the car radio which had a half assed limiter added.

These days 30W into a good high home antenna has no problem at 100-250 miles during the day with no band noise. Ive run the AF-67, DX-60, and plate modulated Adventurer that way several times using a slightly souped up S-40B out on the picnic table.

When 75 is hot its hot as Ive found out on SSB using 30W from a Radiokit mobile xcvr at home and receiving 20 over 9 reports from Europe. Maybe this next season I'll try some QRP AM down with the DX end of the band.

[Bill, KD0HG]

IMO, there's nothing wrong about running positive peaks > 100%, especially if one is running flea power! Do it!

You don't hear much audible distortion on most receivers until you hit 125% or more. If the received signal is on the weak side, any distortion will be masked in the noise.

[WD5JKO]

IMO, there's nothing wrong about running positive peaks > 100%, especially if one is running flea power! Do it!

You don't hear much audible distortion on most receivers until you hit 125% or more. If the received signal is on the weak side, any distortion will be masked in the noise.

  Well said Bill,

   Early in my ham career I had a 6L6 final modulated by a pair on 160m AM. The modulator was class Ab2 driven by a 6SN7 through an interstage transformer. I literally modulated the snot out of that thing as evidenced by the RF final plate current swinging up on audio peaks, and a #47 lamp linked to the RF plate coil getting real bright when I talked. Anyway, it was Christmas time 1975, and the noise was low from my W8 land location. I worked coast to coast that winter anybody that I could copy with my big inverted L antenna and S40B receiver.

  I later redid the modulator with a phase inverter as driver, class Ab1. That boosted the fidelity considerably at the expense of modulation power. After that I was limited to local QRP type operation. With low power like that and average modulation, it seems that the skip scrapes off the sideband energy leaving just a carrier.

Jim
WD5JKO

[k4kyv]

IMO, there's nothing wrong about running positive peaks > 100%, especially if one is running flea power! Do it!

Of course, if the positive peaks are square, distortion and  splatter will result at any percentage of modulation. The FCC allows broadcast stations to run up to 125% positive. The distortion from extended positive peaks (as long as the modulator and RF final are not being driven into saturation) lies in the receiver detector, not inherently to the signal. A simple diode detector probably won't handle much beyond 125% positive; that's the only reason I can think why the FCC capped a limit on it. If the transmitter has the undistorted head-room capability, modulate to 100% negative, and let the positive peaks go where the may.

[K5UJ]

A simple diode detector probably won't handle much beyond 125% positive; that's the only reason I can think why the FCC capped a limit on it. If the transmitter has the undistorted head-room capability, modulate to 100% negative, and let the positive peaks go where the may.

The positive % limit had more to do with the loudness wars--what was happening was stations were doing things to get these really high positive percentages--150, 200 and more in one or two cases.  They were starting to cause headaches for stations on adjacent channels, even with the geographic separation.  FCC eventually limited the positive modulation percentage to restore order, but that was then.  Who knows what today's FCC would have done.   

[ka3bvj]

This ka3bvj I run low power on 40 if no problems.I use a Hallicrafters HT 40 and a dipole.

[KD6VXI]

A simple diode detector probably won't handle much beyond 125% positive; that's the only reason I can think why the FCC capped a limit on it. If the transmitter has the undistorted head-room capability, modulate to 100% negative, and let the positive peaks go where the may.

but that was then.  Who knows what today's FCC would have done.   

Figured out who had the bigger pockets, and taken the license away from the peon's complaining


--Shane
KD6VXI

[WD5JKO]

IMO, there's nothing wrong about running positive peaks > 100%, especially if one is running flea power! Do it!

You don't hear much audible distortion on most receivers until you hit 125% or more. If the received signal is on the weak side, any distortion will be masked in the noise.

  I think we missed Bills point. I contend that the difference between a positive peak at 75% an 150% can be night and day when the carrier level is at the noise level. Either you copy the guy or you don't. Any distortion products at the transmitter end don't matter much because you are QRP anyway, and the distortion products to all but maybe a local ham will be masked by noise. The receiver distortion if it does not follow the high peaks exactly, will still increase the average (more area under the curve), so the recovered audio is louder, albeit a little fuzzy.

I am not saying to blast the modulation into square waves, or run at that high level all the time, but having the capability to put more sideband energy on a QRP carrier is nice. What we do not want here is a mere 75% capable QRP rig with a lot of low frequency audio. The Retro75 gets away with ~ 75% capability by lopping off the audio below 500 hz. They run pretty audio restricted at both ends of the audio range. I have 150% capability with mine, and a little more bass. The bigger Mod transformer that I use is good to 80 hz (100%) whereas the stock one saturates abruptly between 400-500 hz.

Jim
WD5JKO

[kg8lb]

Then again , operators of other modes often postulate that AM makes no sense at any power level