The AM Forum

Now that my Kenwood seems to have gotten sick, I was thinking of cobbling together quickly something for use until I can get the Kenwood figured out.

I do have projects on the go, but projects take me a lot lot longer these days to do than in the past.

I know that I can work nearly cross country on 20 and 17m with less than 30W, even as little as 5W seems to work wonders depending on the band and conditions.

But that's with SSB. What about AM? A quickly cobbled together breadboard rig would probably be only AM. To work 20 and 17m bands how much AM power would realistically be required to work cross country?

Thanks and 73s,
geo VE3GZB

George,

On 10 and 12, I've used a Cobra 29 LTD Classic.  It does about 4.5 watts of carrier, and PEP close to 20.  Negative peak limiter included :)  2SC1969 as the final amplifier.

I use an MFJ259B as the 'VFO'.  Feed a 14-16 mhz sig into the tripler input (it takes 10.240 mhz / two,  then  triples thats to a 15 mhz feed for 11 meters).

So, to answer your question, a 5 dollar radio on craigslist got me on 10 and 12, and I had a BALL with a real antenna on it.

And no, the MFJ is NOT a replacement for a real VFO, it's got a modulated output.  The PLL in the radios I used doesn't care, it's only used as a reference sig.


--Shane
KD6VXI

Why not? The Retro 75 and REtro 40 can do the job at a couple of watts each depending on conditions.  All one needs is a good antenna.  Under high static levels why waste your time with QRP AM.

Well, I can't speak directly to the higher bands, but the QRP AM net that was running last winter had good coverage here, with stations from all over New England & New York checking in with anywhere from 15 watts and down.  I could copy almost everyone when ever I listened in.

ROTFLAMO! That's the first time I ever heard of such a use for that, very clever!!

73s geo

I know exactly what you mean ;D ;D

We will re-energize the AM QRP activity as the noise mitigates this Fall. The timing of the QRP Net was perfect for short hop work and stations were easy to copy, some running only 500 mW. My QRP rigs were a 50C5 modulated by a 50C5 and a 6AG7 suppressor grid modulated with a transformer and carbon mic. There were all kinds of crazy rigs on from Software defined to cakepans. Lots of fun.

Mike WU2D

I run AM at times with an early and late Meissner Signal Shifter but on 40 and up; havent even attempted 160/80. Modulated by 6005's. Worked WAC on 10 and 15.

Carl

It gave me the idea to get a DDS.  The MFJ drifts SO bad it isn't funny.

BUT, it DID give me the 'proof of concept'.  Most of the AM only radios will retune JUST fine to 12 meters. 

I'm going to try 15 next time I'm playin with it.

Life's too short for QRP.

Very nice rig Mike, congratulations!

Actually QRP can be fun!

So far on 20 watts I worked Missouri and Kansas, on 10 watts I've worked Montana and Florida, On just 5 watts I've been able to communicate to Idaho, Mississippi, Florida, Massachusetts. On just 2 watts I was able to communicate to Massachusetts, Arkansas & Iowa.

And I was just barely audible in Florida that same evening on just 2 watts though my antenna is fixed-aimed East-West.

I do have a linear now, I got it from a ham in Quebec. I don't use it often because the presence of CATV lines so close to the south side of the house - where my antenna mast is - makes TVI a bit of a risk. And working constantly in high power is also illegal (hams should always use the minimum amount of power to conduct communications).

But working an RA or a ZL needs more hamsters on the treadmill.

73s geo

i never did like that minimum amount of power necessary rule, just how do you judge the minimum amount of power? the more power you run, usually the better you are heard. so do you run enough power to be just barely heard or do you run enough for it to be comfortable to listen to? there are some situations such as when trying to run AM in high static when the minimum amount of power needed to communicate is the maximum you can put out.

I seem to recall a very similar question posed and lengthy discussion here when you built that QRP breadboard rig for 40m(?) a couple years ago, Geo. The same principals still apply.

Some of the folks on the Texarkana Traders Net run only 15-25 watts of carrier and are heard well. These are usually old military rigs which have plenty of 'talk power' and I presume their antennas are high and well-made.

I can't get away with 20W from the ricebox and have to use 100W carrier. It may be the time of day, frequency, and antenna, which seem to have more to do with it than the power level itself.

Agreed, fully, 100%

QRP AM, especially on a noisy night makes about as much sense as a fart in a space suit! ! !  And if you are running a compromise antenna, you are really fighting a losing battle. You might get away with QRP AM on the higher bands like 10m, but on 75 and 160 it's.......................

"BANG, lookie here, squashed just like a bug"   ;D

 QRP can work quite well, even on 75 AM. Of course the conditions need to be tasken in to consideration. It is not for everyone but there are quite a few having fine results . Had quite a few rag chew QSOs at distances of up to 600 miles, using the Retro 75 , 2 watts prime time on 75. Even with the wide barges (They think of themselves as "tall ships" operating in the area !
   Go for it !

Y'all QRPers need the "wide barges" to keep it clear for y'all and blast a hole so the slopbuckets dont squash ya like a bug.................  ;D  ;D

Sure it'll work real well. I've use the Drake T4X barefoot (20 watts) every weekend on 80&40 with good reports. It's a lot of fun.

But chose your op times and freqs carefully. You don't wanna run a motorized skateboard on the interstate at rush hour.

If 10 meters opens again, then QRP AM might work on that band.

It's a lot of fun.
My homebrew creation does 2 W on 80M and I'm frequently surprised on how well it does.
Make sure to modulate it well. I've heard a few QRP'ers on the NE QRP net this winter that could use a little bit more audio. The next TX on the bench will hopefully be doing about 40 W.. which is still QRP for a lot of you guys  ;D

Frits

Nope, never needed "wide barges" that I can recall. Positively never wanted one. ;)
 When conditions are good , QRP works FB. The wide barges are no more trouble than the sidebanders. We worked Steve , WA1QIX on Rattlesnake Island last Sunday with the Elmac @ 37 watts with 20 over 9 sig reports. I am certain the Retro would have worked pretty well .

  Mike, N8SDD lives a few miles away.  We often zero beat the  wide barges with our Retro 75s and talk right thru them .   So , even when the band is sufferring from an east infection we are able to operate 75 AM quite easily. 20 meters should be just as viable.

Of course QRP isn't for everyone . Many others however have had fine results with a decent QRP station.

 Sure, QRP will work on 10 . It also works well on 75  ;D

Yes! just today i have done a very nice qso with the setup you can see.... my recently restored HW TBC-50C i received very good reports!

20W carrier.

Its all in the antenner..... the better the antenna, the better you'll get out.


Is the 'wide barge' like the 'wide stance'  ???? ??

klc

Miscellaneous thoughts on QRP:

A rich man once said, "I've had low power and I've had high power and believe me, high power is better."   ;D

In my first salad days as a ham, I recall seeing messages in QST advocating low power repeatedly.  Editorials, articles, occasional opinions by columnists all saying no one needs to run more than 100 watts blah blah sprinkled through issues of QST once or twice a year for years on end.  At the same time, I'd see ARRL staff members' shack photos in contest results and there'd be a SB220 in nearly all of them.  Hmmmm.  It took a few years to start feeling like a sucker. 

I wonder why all the sw and mw broadcast stations aren't running 20 watts.

I like armchair copy and am glad the station I'm working is running a T368.  I can also hear my 20 watts Q5 no problems.  What else matters.

No matter what power level you run........

PUT SOME AUDIO ON IT!!

That is one thing no one ever has to tell me  ;D  ;D


Always remember the first rule of the piss-weaker:

THE WEAKER THEY ARE THE LONGER THEY TALK!  >:(  :o

 Lessee here. Who else matters (?) Two fellows in MD living about 5 miles apart running the legal limit . Sure they can hear each other. But the fellow in Kentucky may not be able to hear another station in Ohio Tnx to the QRM.

 What else matters ?
Why don't broadcasters use 20 watts ?
In a thread that simply asks about the viability of low power AM ???

  Some folks may not care to run QRP AM, that is a different matter. Still others operate QRP AM regularly with good results.
We are not broadcasters in any event. That is why we have a lower power limit and a gentleman's guideline to run lower power when possible.
  We usually run lower power here but the legal limit is just a flip of the switch away if wanted (but rarely needed) ;D

 Of course , as Buddly sez, modulate well.
 The QRO bunch manages to fillibluster too , Mr Slab  ;)

 Old sayings ain't always so.

They sure do and often 10dB less than that. Lots of day/night stations have to both reduce power at dusk but also change antenna pattern if they are a multi tower station.

A QRP 2W to a big stick is still enough for local listeners within walking distance. My favorite station is WXEX 1540 which is 5KW day, 2500W at critical time and 3W at night. I need a good outside antenna or Beverage during the day as Im already in the fringe area. Not a chance of hearing at night so I use the PC to listen to them.

WJIB is 250/5W and is OK during the day until the Toronto flamethrower takes them out.

I don't have Part 97 right here before me, but IIRC, it says minimum power necessary to maintain the desired communication. Now, what exactly does that mean? Minimum power to remain full quieting? Minimum power to maintain 100% readability? Or, does it mean you are supposed to always run right at the ragged edge? Plus, while you are transmitting, you have no way of knowing what the signal is at the other end if the other station is beyond ground wave range.  It would seem to me that rule was meant to discourage a couple of stations a couple of blocks apart from each running a KW on 75 just to chit-chat with each other, when they could be using VHF or only a few watts on one of the lower frequency bands. Once outside the local area, there are too many variables to make a citation stick for running more power than "necessary".

this is what it says:

FCC 97.313 as of August 17, 2011 -
www.hallikainen.com/FccRules/2011/97/313/

(a) An amateur station must use the minimum transmitter power necessary to carry out the desired communications. ...

I desire armchair copy.

<<<"Why don't broadcasters use 20 watts ?"

They sure do and often 10dB less than that.>>>

I apologize for being in a hurry and not choosing my words more carefully.  I should have asked (rhetorically) Why don't broadcasters use 20 watts all the time?

<<WJIB is 250/5W and is OK during the day until the Toronto flamethrower takes them out.>> 

you mean "squashed like a bug?"  :D

Those ham radio articles harping on 100 watts  - well OK it works fine for SSB much of the time but a bit more is needed to do the same on AM. The articles may have been focusing on the lowest common denominator not the classical modes.

100 Watts is very doable.  One has to choose band and time to operate.  A LOT OF US in here use 100 Watt rigs.  Oh wait, you're comparing apples and oranges.  100 watts "SSB" is P.E.P.  100 watts AM is carrier.... or do you mean 25 watts carrier and 100% modulation?

OK, We'll open a leg of the three phase and adjust the bias to match. ;)

All the HF bands are big enough to handle a lot of QSO's, both big & small, no? ???

100W TPO > 90% avg mod AM is a good level for local stuff. :-*

I've a hard time telling the difference between slopbucket and noise. :P

73DG

> Does QRP AM make any sense?

 Absolutely! Just make sure propagation is favorable, QRM an QRN are down, keep the average modulation high, and don't stay keyed down too long. QRP AM has some special considerations to take in. As said earlier, "old buzzard" transmissions on a low power AM signal that might also be under modulated will upset those in a big round table. If you check into a group of AM'ers running QRP, maybe keep the transmissions under 30 seconds each. That way the rest of the group will not lose patience with you as QSB or QRM covers you up.

Several have mentioned the Retro-75. Just remember that this QRP AM rig as designed has a low average percentage of modulation since the AMC kicks in early, and the modulation transformer saturates on audio peaks. There are several long threads about this on AMFONE. Easily fixed issues..

Jim
WD5JKO

Still it is not a question of personal preference. It is about the viability of QRP on HF AM. Some proclaim QRP is not viable on HF AM..Others who have actually tried it have met with good success and operate QRP regularly. Not only "Local contacts" but even  500 to 600 miles with 2 watts on 75 AM "prime time" with good results.
73, Gary

actually, building a really good QRP rig and then feeding it into a linear amp is a great approach. You can do all the modulation and RF stuff at low levels where component cost/size etc is not much of a problem Then when you've got that QRP rig running 5-10 watts output with good modulation and all that you can pipe it into the linear if conditions are rough.   

QRP would be like a separate category or challenge, to me. Maybe on a higher band, possibly 40M, but more like 20 and higher, the atmospherics are much less and won't cause a ruckus in your ears.
The lower bands and the QRN would be too much for anything beyond 1 minute and 'hey I just contacted a Ham in Minnesota with 5 watts AM'........200 miles from my QTH on 80M!!

george..there is a guy in orangeville, selling a johnson viking2....listed on the o.s.s. ..i think he is ve3pri...the old viker, is hard to beat...

..tim..

..sk..

Could someone define "QRP" for me?

2-watt tuna tin, a 50-watt Ranger or Elmac?

Out here in the Great American Desert, it's a thousand miles + to population centers. Over land. ~500 miles makes it to Albuquerque, Salt Lake or Omaha. Most of y'all are real DX. A barefoot Ranger just won't cut it. I'm with Don on this one.

Indeed.  What Ed said.  Maybe build a Doherty for single-band op.

73DG

Fred,
 I often work other stations at 200 miles plus . We have worked Retro 75 to Retro 75 at those distances easily and had some nice , long QSOs. The very first night I had mine on the air we made contact with a station in TN near the GA border (500 Miles Plus with only 2 Watts), he was in QSO with a SC and a PA station . We chatted for about an hour and I repeatedly asked if they wanted me to put on more power. They said the 2 watts was FB and S9+ .  One of those hams is now running a Retro 75 of his own.
 As someone said "define QRP? Last week I was in QSO with Steve out on Rattlesnake Island using the Multi Elmac @37watts and gettin S9+20 and better reports. Steve was perfect copy here as well using the excellent receiver side of the Retro 75 So , yes "QRP" is quite viable even on 75M. even at 500 miles 50 to 100 watts is quite often entirely adequate. Given good conditions and 2 watts is not only adequate but great fun.I have a few operating positions here ranging from 2 watts to the legal limit. I rarely ever find the need to use the limit  however. The most used TX here are Elmacs @37 or so watts...CARRIER.Next most used is the Viking 1 @ 100 or so . The Globe Champ and the HB legal limit are rarely even needed. And we don't even have the mandatory OWL feedline ;D As far as running an amp with the Retro 75, not for me. It really defeats my reasons for building the Retro. Just finished the Retro 40 but have not had the chance to try it out yet.
 George, If you really NEED more power you can have my Viking 1 real cheap...or one of the Elmacs...or perhaps the Globe King 500..CHEAP. PM me..I don't need the stuff.

 Carl, Just for the sake of clarity , I was repeating the question already posed. Not asking it myself. I was actually a bit surprised that anyone with a license had to ask !
 Thanks for the input however.

George,
Why not try DSB. You can build a tiny DSB board for a Heathkit HW8 that works gangbusters.
Check Google for DSB and the HW8. It'll fit into almost any small AM set. You can convert a CB and use it there
When you talk to SSB, they don't even know there is another sideband.
Jim VE3DDY

With folks listening hard and using good antennas, and by restricting the QRP Net to Fall-Spring and avoiding the QRN and then loading the bases by optimizing the time to the late Sunday afternoon before sunset so short hop works well, and picking a frequency below the AM window, IT SIMPLY WORKS.

There's a difference?

Let Us Now Praise Famous Strappers


Breaking news:  Scholars of the Dead Sea Scrolls have pieced together an extension of
Ecclesiasticus chapter 44, unknown before now.  It appears to be in praise of famous 
strappers according to what can be gathered from the ancient texts:

Let us now praise famous strappers and the radio fathers of the ancient knowledge before us.

They had great glory through great power from the beginning of Eimac.

Such as did bear rule on the bands, men renowned for their class C power, giving counsel by     
their vast knowledge of the ancient circuits and declaring future inventions:

Leaders of the noobs and piss weakers by their counsels, and by their knowledge of learning       
meet for the AMers stuck on city lots, wise and eloquent are their instructions:

Such as found out the angel music of AM, and recited the laws of impedance ratios in writing:

Poor hams furnished with homebrewing ability, living peaceably on the low bands:

All these were honored in their generations, and were the glory of their times.

There be of them, that have left a nickname behind them, that their praises might be reported     
in ER.

And some there be, which have no memorial; their QSL cards perished, as though they were
printed on cheap paper and had never been; and are become as though they never modulated with     
1.5 times their carrier power.

But these were merciful strappers, whose high dipoles hath not been forgotten.

With their knowledge shall continually remain a good inheritance, and their Novices are
within the AM community.

Their keys and microphones are silent in peace but their name liveth for evermore.

The slopbuckets will tell of their wisdom, and the AM community will shew forth their praise.

Yes I mean the 100W PEP, is fine for SSB, but a 100W PEP AM signal (25W carrier if that is so), like comes out of a typical ham transceiver in QST, is more challenging for AM. I meant that the people that wrote it might have disregarded AM. Sorry for the confusion, I have not seen more than 1 or 2 of the articles so I don't know, only speculating their reasons.

I currently run a Yaesu FT-897D on HF. It's a 100W SSB radio, with 25W AM carrier. I've talked to wondrous places far away on slopbucket, but an attempt to talk 20 miles on 160 meter AM met with failure. Admittedly, the antennas on both ends were, uh, less than optimum. We've yet to try on another band -- still due to antenna issues, but I'm really working to get the DX-100 on the air and have some sort of reasonable power on AM. Given the QRM/QRN conditions here in TX, I'm not really optimistic about the chances for QRP AM. However, it may work in some locations or with better antennae than I've got.

ldb

 Roy, K8VWX just checked in to the DX-60 net using his new Retro 75 2 watt rig. Received fine signal reports all around. We flipped the switch and went over to the Retro 75 here worked Columbiana ti Detroit FB . QRM from the Magnolia net and the QRN were no problem. Roy usually runs his pair of 4-1000 mod by 4-1000s and seems to be enjoying the QRP after all these years.
Congrats to Roy !

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

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

 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.

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

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.

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

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.

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.   

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

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


--Shane
KD6VXI

  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

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