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Assisting AM Newcomers




 
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N1BCG
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« on: March 29, 2018, 09:47:13 AM »

Two great things I've noticed over the past few years is the steady increase in ops who try out the AM mode for the first time and the helpful guidance provided by experienced ops in getting their settings right. Most of the newcomers are sidebanders who come across AM signals and are drawn to the refined audio quality.

The basics for adjusting most multimode rigs for AM are simple: Reduce output power to 1/4 or below of the PEP capability of the transmitter, and if applicable, defeat the ALC with the battery circuit designed for this purpose.

I found an exception worth noting. A friend with a 200W Yeasu FT-2000 sets his power to "50 W" according to the digital display yet his analog power meter and external meters showed less than a 10 Watt carrier. As an experiment, the digital reading was increased to "130W" and that yielded a carrier output of  approximately 30 Watts on the rig's analog meter and external meter.

I don't know how common it is for manufacturers to compensate for AM operation, but it's important to keep this possibility in mind going forward.


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KD6VXI
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« Reply #1 on: March 29, 2018, 01:22:04 PM »

Maybe the FT2000 is setting the power output at a pep level, and it auto compensates for the 1/4 carrier level?

Seems the discrepancies in power out could just be related to accuracy of the meter(s).

--Shane
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Patrick J. / KD5OEI
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« Reply #2 on: March 29, 2018, 06:29:47 PM »

A modulation scope will be a great help setting up AM best.
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Steve - K4HX
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« Reply #3 on: March 31, 2018, 12:03:23 PM »

A newcomer is unlikely to have a scope.

Does your friend have the 100 or 200 watt version of the FT2000?
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W4OS65
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« Reply #4 on: March 31, 2018, 12:25:19 PM »

The AM bug has bit me. I am in the process of building the Bob Heil "Pine Board AM Transmitter" for  40, 75 & 160 meters. Been a Ham for over 40 years. Have never operated AM.  Looking for an AM tube receiver for a beginner.   Been looking at the Hallicrafters.  Recommendations Please.
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Carl WA1KPD
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« Reply #5 on: March 31, 2018, 01:14:33 PM »

For AM top of ther line would be the SX-28, the SX-71 has a respectable showing in that mode.
Personally I love the looks of the SX 16 or 17.
Once you start to get into the later models they were designed more for SSB and do not perform as well on AM.
But just like there are Chevy's and Fords, we all like different things.
I also thing the NC 300 or 303 is a very respectable performer and within a reasonable price range.
Welcome to AM!
Carl
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WD4DMZ
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« Reply #6 on: March 31, 2018, 03:35:53 PM »

Greetings. I have about 20 assorted boatanchor receivers including Hallicrafters, Hammarlund, National, Drake...

My original preference was Hallicrafters SX100 or 101 or 122 but for the last two years mostly use Hammarlunds for Rx. Th HQ 180 and 170 have the best selectivity but the bandpass is strictly for communications. The HQ 145 and 150 have good AM quality audio. Typically I have the HQ 150 paired with my Viking 2 but if band conditions deteriorate I switch to the HQ 180. My HQ 145 is paired with a Ranger 2.

If band conditions are really clear and clean I will occasionally switch on the Hallicrafters SX 42. With two 6V6 tubes for audio and a big Jenson base reflex speaker I can rattle my windows. However, selectivity is an issue. I believe the SX 42 was the successor to the SX 28 after WW2. The SX 42 will also give you a nice sounding FM band radio,

Another good sounding Hallicrafters is the SX 25. Two 6V6 audio tubes. But, WW2 era selectivity and not very sensitive above 20 meters. Pretty easy to work on.

Having worked on so many different boatanchors I will say the Hallicrafters are the most difficult. Lots of paper and black beauty caps to replace, many in impossible to reach locations so be forewarned. Also, the older Hallicrafters have 500 or 5000 ohm audio output Z so a matching xformer is necessary if you do not have a matching factory speaker.

If you do not need a SSB detector in the  radio, I'd go with the HQ 145 or 150 route. Lots of room inside to work on them and lower in the cost range with pretty good AM audio quality. Audio output Z is 8 ohms so any good HiFi speaker will give good results.

Have fun.

Rich

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Carl WA1KPD
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« Reply #7 on: March 31, 2018, 04:43:46 PM »

Agree.
I love my HQ 129 and 140x
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KB2WIG
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« Reply #8 on: March 31, 2018, 07:15:17 PM »



I've  pared my Viking2 with an HQ145 and have few regrets.

klc
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WD4DMZ
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« Reply #9 on: March 31, 2018, 07:19:20 PM »

If I ever find a clean and reasonably priced HQ 120 (maybe a 129) I would add that to my AM station.

Rich
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Steve - K4HX
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« Reply #10 on: March 31, 2018, 08:16:01 PM »

Suggest you do some reading at the links below.

http://amfone.net/Amforum/index.php?topic=6059.0

http://amfone.net/Amforum/index.php?topic=4779.0



The AM bug has bit me. I am in the process of building the Bob Heil "Pine Board AM Transmitter" for  40, 75 & 160 meters. Been a Ham for over 40 years. Have never operated AM.  Looking for an AM tube receiver for a beginner.   Been looking at the Hallicrafters.  Recommendations Please.
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WD4DMZ
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« Reply #11 on: March 31, 2018, 11:45:45 PM »

Excellent write-ups. Thanks.

Rich
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WE1X
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« Reply #12 on: April 01, 2018, 09:11:34 AM »

Well...thanks to WA1KPD I too became an AM newbie.  For the most part I've been buying, tinkering with and selling receivers although about 6 months ago I picked up a Johnson Ranger. What I've learned (among other things) is each receiver has its own personality and quirks. Today's shack has 11 receivers including a complete Collins A-line. As for AM audio quality I found the 75A-1 with the Bill Orr mods and the HQ-129X to be great.

Harry WE1X
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w1vtp
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« Reply #13 on: April 01, 2018, 11:08:35 AM »

A newcomer is unlikely to have a scope.

Does your friend have the 100 or 200 watt version of the FT2000?

Since your friend has the 200 watt version1 and assuming he doesn't have a scope (and dummy load that will handle 200 watts). I'd be tempted to offer to come over and bring my own scope and load and take a look at things. Meanwhile a look at the manual might yield positive results.  

Al
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1 See initial post from Clark
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N1BCG
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« Reply #14 on: April 01, 2018, 05:38:28 PM »

Fortunately, my Yaesu FT-2000 friend understands the importance of keeping his modulation in check and purchased an REA modulation monitor.
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Steve - K4HX
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« Reply #15 on: April 01, 2018, 10:22:41 PM »

He should've purchased a scope - much more useful. ;-)
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MikeKE0ZUinkcmo
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« Reply #16 on: April 02, 2018, 01:24:23 AM »

There are a lot of decent older receivers out there, and as someone mentioned earlier, each has it's own personality.   I don't have a strong bias for one maker or the other and have a few of what I consider the better examples made by each manufacturer.   

Within the National line of receivers, I like the NC-2-40D, HRO-50, NC-183, and NC-303 all good AM receivers.   Although the NC-183D is, in my opinion, the prettiest general coverage receivers of the era, with fairly good performance, I don't like it much as a comm receiver.    The fabled R390 and the quite different "A" version, are considered by many to be the best HF receivers ever built.   They are pretty astounding, but are not unlike driving a tank, and not a pleasure to cruise the bands with.   

The Hammarlund HQ-129X is certainly a nice receiver as is the HQ-170, and SP-600.   The SP-600 is an excellent, if not the best band cruiser ever,  with great performance, even though knowing "where you are" is a bit of a mystery.   There were close to 30 "JX" variants of the design, all optimized for a particular type of service, with the JX-17 being the most common by far.

The Hallicrafters
SX-101 is a very good receiver.   The SX-100 is another "pretty" receiver, and electrically nearly identical to the 101, but, its a smaller, cheaply built cousin of the 101, and the frequency shifts significantly just from a rap on the table.   The legendary SX-28, a monumental player in WW II, is another excellent receiver, and more than fifteen thousand were produced.   I have one waiting in the queue.

Tthe SX-73, a running mate of the Hammarlund SP-600, the SX-88, SX-115, and its less expensive cousin the SX-117, are also very good receivers. 

Though very long in the tooth, the venerable RCA AR-88, and the Canadian CR-88, both of which had a few variants, is another of the famous WW II receivers with somewhat more than twenty thousand having been built.   This is one of the "classic" receivers and actually a somewhat impressive radio. 

Most of these receivers can be found for as little as fifty, to over 300 to 400 bucks on any given day, and a few of the "legends" for as much as 1500 Dollars.   In the 50 to 100 dollar range, a "5" to "6", both from a cosmetic and electrical standpoint, aren't uncommon, but of course these are project radios.

For those unfamiliar with old AM gear, a few google searches will keep you up late, several nights. Wink
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Mike KE0ZU

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WO4K
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« Reply #17 on: April 02, 2018, 06:21:47 AM »

One of the very best basic tutorials on the functions of AM transmitter circuits was written by Dr. Greg Latta, AA8V. On his website he takes a Viking Ranger schematic and breaks it down into 19 basic circuits (VFO, audio and power supplies, clamp, oscillator, etc.). Then he explains, in easy-to-understand language, the functioning of each circuit and the component parts within it. Great stuff for any newcomer with an interest in AM. See:
http://faculty.frostburg.edu/phys/latta/ee/ranger/schematic/rangerschematic.html
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W4OS65
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« Reply #18 on: April 03, 2018, 09:16:11 AM »

I would like to thank everyone. For all the useful information. I have found a real clean Hammarlund HQ-170A. Have downloaded the manual. Now need to get back to work building the Pine Board AM Transmitter.

Hope to be in the AM window before long.

Ronnie G Kelley - W4OS
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WD4DMZ
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« Reply #19 on: April 03, 2018, 11:09:32 AM »

This thread has encouraged me to fire up neglected boatanchors in my collection. At the moment I am listening to an FM country station using an SX 62A and the matching bass reflex speaker. Very nice sounding radio.

Also, I have a National NC 303 and Hammarlund HQ 170A in deep storage. Both are a bit rough but functional. Need to make room for one of them.

The 170 has one annoying issue that I could not debug... it motorboats on the 2 KC bandwidth position. Anyone have any idea what might be causing this? Every other function is ok and the tubes check out good.

Rich
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Todd, KA1KAQ
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« Reply #20 on: April 09, 2018, 09:36:23 AM »


The basics for adjusting most multimode rigs for AM are simple: Reduce output power to 1/4 or below of the PEP capability of the transmitter, and if applicable, defeat the ALC with the battery circuit designed for this purpose.


One thing you could add to that list Clark is to shut off the processor switch. Probably counter-intuitive to most ops who are used to operating SSB.

And yes - definitely leave some headroom for voice peaks when tuning up.

Have worked a number of folks over the years who were new to AM including a couple who worked me cross-mode then felt brave enough to turn the mode switch to AM. A little time and patience goes a long way.
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N1BCG
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« Reply #21 on: April 09, 2018, 01:33:42 PM »

One thing you could add to that list Clark is to shut off the processor switch. Probably counter-intuitive to most ops who are used to operating SSB.

Thatís a good point. Itís also unfortunate, in my opinion, that most processor functions also include a dramatic change in EQ. I get that the manufacturers are trying to make things simple, but having a good bit of compression without the mandatory space shuttle audio would be helpful for all voice modes.
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ka1tdq
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« Reply #22 on: April 15, 2018, 08:18:33 PM »

I started out with a single FET class E rig before I went with high power. Someone should put plans out there again for a single FET rig for newcomers (maybe Heising modulated since itís simpler). Pair it with an SDR play and youíve got a very capable station.

Jon
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N1BCG
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« Reply #23 on: April 15, 2018, 08:58:47 PM »

Exactly, although a 2 FET rig is the practical minimum as you need even numbers for adequate harmonic cancellation. That gives you a decent 100W carrier which is perfect for getting started. Circuit boards are out there for simple Class H modulators, and while they can accommodate enough FETs for legal limit, newcomers can begin with just a few, and that would only require a modest power supply. Additional FETs can be added to those boards for future increases.
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