Gary's Awesome Adventures in Amplitude Modulation (AM Radio Transmission & Reception)

This is what I call my "AM" position at Station WD4NKA.  I have a few positions at the control console.  I also have a "NRR" position, a medium power code position for "Novice Rig Round-up" events which is entirely Hallicrafters "Grey-Line" 1961 equipment, and the other is my Sideband position, essentially a Kenwood TS-120-s.   This installment, however, will focus on the on-going evolution of my AM position, which has posed a real challenge, and for several reasons:

1.  I live on a small residential lot.  Approx 75 feet by 50 feet.  This pretty well precludes full sized wire antenna types in the main.  At least, the half wave dipoles.

2.  I already have a full quarter wave vertical and radial field for my 40 meter work bolted to the gable end of the house.  At least I did until early summer 2019, when after years of service, a storm damaged it, and it had to come down.

3.  I have limited space and limited power supplied to my radio room, which is shared with my Letterpress Print Shop which also pulls it's share of current.

4.  I have a sand pile for a soil substrate.  I live on a sand pile, essentially.  Historically awful to nearly non-existent ground. (ergo the elevated 40m vertical!). Not good for RF grounding.

5.  I have a sweet wife that puts up with my various avocations without complaint, but who also really doesn't want the house to look like a bird trap for condors.  The neighbours would also like to maintain their property values.

6.  I live in "Hurricane Crossroads", which proved itself in 2004 when in three months three hurricanes criss crossed over my roof.  Yeah.  Whatever I put up has to come down, and sometimes with very little notice and no, I can't take off work if the down-time comes in the middle of the week.  So whatever goes up must come down inside of an hour.  Completely down and secured.

Add this to a huge interest in Amplitude Modulated wireless signal.  I guess I love the way a receiver behaves when it intercepts an AM signal and extracts what is often some very nice sounding audio.  It's a nostalgic sound.  It involves nostalgic equipment more often than not, although lately some very nice digial AM equipment has come to the foreground.  But as a former MWdxer and low signal buff in general, I love the challenge of AM low signal work.

Getting Set Up
I already knew that while my early AM exploits (I had a Hallicrafters HT-37, Johnson Courier amp and a National 303, later a 300 receiver about 20 years ago) took place on 7290kc, these days most of it seems centered around the 75 meter "AM Window", 3880-3890 kc, most specifically 3885 kc.  I had nothing on the roof that was actually designed for 75m.  Nonetheless I was up to the challenge, so, about two years ago I began my re-entry into AM by trading my HQ-170 for a "Red Letter" HQ-129-X, a truly awesome AM receiver, and not too shabby for cw, either.  These became my ears.  I kept my extra HQ-170 speaker, btw.

But what to transmit on?  My DX-40 was great for cw, but it's audio section needs rebuilding.  My HT-40 is a good prospect at 15 carrier watts, but wait.... what about my Yaesu FT-101EX?   I found I could get about 25-30 watts carrier safely from it's rated 120 watts PEP.  And, it would take my old HT-37's mic, my 30 year old amplified Astatic D-104 without modification.  The FT-101 and D-104 have since become inseparable.

The opening photo shows what I arrived at for apparatus.  Yes, I have to switch, manually, between the transmitter (FT-101EX) and the receiver.  But I grew up doing this as a Novice for my cw rigs, it's all old hat to me.  All of this was to play through my newly rebuilt 33-ft 40 meter quarter wave vertical, now sporting brand new aluminium tubing from DXengineers, and about ten 35 foot radials fanning across the roof.  It is a stunning performer on 40 meters!  But for 75 meters, it's only an eighth-wave length vertical!
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This is the vertical, base fed through a coaxial RF choke.  The feed point elevation is approximately 20 feet from average terrain.  It is quite heavy, so  I have it bracketed to about five feet of extended mast for windage purposes.  It does not seem to have a coupling effect on the antenna at all.  The base of the antenna sets in a 5 foot section of Schedule 40 PVC.  Any coupling to the mast seems to be more than offset by the fairly large radial field.

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This is a shot of that "radial field", which may look a bit confusing.  The red wires are the radials, the black lines are shadows.  The radials are elevated about two feet and taper downward to the roof level.  At the point this photo was taken, I had about ten radials fanning across the roof from WNW to ENE.  It works nightly into Italy at S9 to 10dB over on 7195, talking to Roberto in Cremona, but then.... he hears EVERYBODY at least S9 with his set up.  But, it makes me feel good, anyway.   Graci, R-r-r-r-roberto!

So, the first real challenge: how to put this antenna on 75 meters?  The most simple and obvious method was using what I had: my Dentron MT3000A tuner!
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That tuner occupies the lower left section of my Hallicrafters 1961 Novice Rig Round-up position.  It's probably the most versatile and most used piece of equipment in my shack, and represents the high-point of Dentron Construction.

So, feeding the coax directly to the tuner and through it securing a match to the FT-101EX, and getting a decent power setting such that my modulation didn't suck back the output power too much, I then proceeded to enter the world of 75 meter AM phone. 

Being Heard

At first I tried calling stations in the evening.  I did manage to raise a few stations, and with mixed reviews over my signal strength which was predictably quite low and frequently victimized by QRM, QRN and QSB.   When I tried to check into a group of stations, I was rarely heard.  These stations were pounding each other with 20dB over S9 sigs, and probably their AGCs were not quite recovered between transmissions, so they really never had a chance to hear my S5 signal.  They were rather rapid with their modified PTT rigs, none of them having to flip switches to cross over transmitter to receiver like me.

You may ask why not just use the receiver in the FT-101?  Passband is uncomfortably narrow although I do use the receiver to zero in on a signal.  The AM filter and installation was about as expensive as my Hammarlund, and from reports I have heard, no where near as nice.  Ergo, the separate AM receiver.  I have to flip it to stand-by and switch the transmitter over to the antenna, so two switches are flipped for transmit, and again back to receive.  I like it.  That's how my CW operation has worked for 42 years, why stop now?

In time, I began instead to try early mornings around 5:30 pm, and check in with the 3885 morning AMers.  This proved better.  At least, some of them could hear me.  Most importantly, they did not communicate annoyance toward my low signal.  This alone pretty much kept me encouraged to continue to improve my station.  You can really shut a guy down from the start with negativity.  These guys were really encouraging to me.

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Antenna Experiments and Adjustments
For the past half year or more, I also experimented with alternative antennas, all wire oriented.  Random wires, quarter wave length overhead wires, various types of dipoles, an attempt at an inverted L, all of which had to go into the trees in the extreme ends of my property where lengths could be the longest, or as in the photo, various "L" configurations.  This one was probably my best wire antenna, going out to the front yard tree some forty feet, then another fifty feet across the yard up at about 30 feet terminating into another clump of trees at the front corner of my property, a total of 80 feet, coax fed, with the braid grounded to a radial counterpoise.  It actually had some merit beyond all my other wire antennas that I could work within my limits with, but over all, the 33 foot vertical still out performed all my wire antennas, as was shown over time on the air switching back and forth over every conceivable operating environment/ band condx.  This was especially true after I installed four radial wires cut to 70 feet.  This seemed to make somewhat of an improvement on my 30-watt signal.  Using this vertical operated, WD4NKA operated mostly between 5:30 am and 6:30 am Eastern Standard time in the Summer, Fall and now Winter, with average results something like this:

Florida Panhandle: below S9, sometimes well below until sunrise, then sharply increases to an average S9- 10dB over. 

North Georgia/ Tennissee/ Kentucky:  I do these regions best, KK4GZQ often doing the role of personal relay for me.  Very often he and other KY and TN stations report me consistently with S9 or above.  Sometimes well below, but on the average, I can be heard well.

Carolinas: I do well there on the average, at least until sunrise.  Frequently well into the morning.

Virginia: Normally reports me as well above the noise, with the occasional QSB dip.  This is on average.  Some early mornings it's better, some far worse.  But on average, quite communicable.

Indiana, Illinois, Ohio, Wisconsin: These are about half and half.  Half the time my little 30 watt AM signal can be clearly heard, half the time poor Kevin, KK4GZQ has to relay.  So, it's a crap-shoot.  When it's good, I sound very good.  When not good, no copy or barely so.

Pennsylvania:  Pittsburgh and Philadelphia often times give me opposite reports.  I am heard on a better average there as opposed to Indiana, although sometimes I think it may be by web SDR, but when I am directly heard, generally I can be clearly understood, if not with a mounting respectable signal.  New Jersey tends this way as well.  Normally, if they cannot hear me well, I also cannot hear them well, and so it is up into New England.

New England States: is pretty iffy.... but generally they report me just as I might report back to them.  Rarely can I hear them well without they not at least copying me.  Generally, if I am at noise level, they are same on my end.  One memorable early morning, Tim, up in Maine, remarked that I should get an amp.  I had to chuckle: I could barely copy him.  In fact, I think Perry, W3MMR may have had to repeat what he said.  Maine, Connecticut, Mass, in general, have never really given me the signals I get from Kentucky or Virginia.  In fact, a PEI station actually came over louder a few times... go figure.

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One thing Tim mentioned along with "get an amp",  was "...if he might try to throw a matching coil at the base of that thing and feed it at that point..."

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Of Course!  The Old "Gotham Vertical" thing!  Thanks, Timtron! -and I immediately set forth experimenting with what coil dimensions I might need.

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I already had a  2" diameter section of PVC wound with Nr. 14 gauge solid copper house wiring, with insulation removed along a strip of the coil permitting tapping.  I connected the center conductor of my coax to a clip, the braid to the radials.  Then I moved the tap, taking swr measures, up and down the ladder to the roof.

Having finally found a good match, I secured the tap and tried it out the next morning with the AMers on 3885 kc.  The results were remarkable!  Increased average signal, and more folks on average able to copy me.  It was frequently remarked by other stations over time what a difference adding that coil made.  So, I wound a permanent coil, installed it, and here we are:
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For those curious of the dimensions, the coil form is sched. 40, 1-1/2" inside diameter, 1-7/8" outside diameter.  There are 14 winds of Nr. 14 solid copper house wiring.  This can be further tuned to an absolute flat 1.0:1 match by adjusting the telescopic tubing, but it was not necessary for me.  As you see it here, the match is 1.2:1, and pretty well maintains that match from 3700 - 4000 kc.  I do have the coax fed through the MT3000A, which has a "straight-through" position, and two other coaxial inputs, plus a balance input and one for a random wire.  I forgot to drill a "weep hole" at the base of the PVC into which the vertical base is seated, so when it rains, I think moisture collects and the swr goes up to 1.5:1, but I can drill a couple holes through the base end-cap.  I will be more than likely enclosing and bracing the coil soon, just to tidy things up and improve the appearance.

So, this is where I am now.  Still at 30 watts mean carrier with about 120 watts PEP.  Still using the FT-101EX and D-104 mic, which I am dis-inclined to cease using.  Here's why:

This microphone focuses the bulk of its energies in the audio mid-ranges.  Mid to higher frequencies, really.  It is a communications mic, and the low level modulation system in the FT-101, along with it's speech amps, are geared also for these ranges.  There is a reason for this: communication effectiveness under low signal and high QRM/N and QSB conditions.  One day, I might try a stab at that broadcast sound.  But that will be down the road.  Next step: 


QRO.

WD4NKA-AM is an ongoing work-in-progress.  Stay tuned!

Low noise and great propagation accompany your New Year!

de wd4nka.