HF AM???

[KD0ILS]

I'll be the first to admit I'm rather new to HF i've had my ticket for 6 years and thought its time to venture away from 2m/440.  I know I'm only a technician and currently my bands are limited to 6 m and 10m ssb but the real question is concerning the two radios I have that could get me going into HF.  I have a hallicrafters HT-40 and a drake tr-4c and rv-4c that was given to me from a silent key and these radios havnt been touched since the early 80s.  I also have 2 astatic d-104 microphones to be paired with these radios but they just need to be rewired for the proper plugs.  The status of the HT-40 is unknown because i have no crystals and the drake doesnt seem to be transmitting on 10m ssb or measuring into a dummy load.  It could just be my lack of knowledge of boat anchors.  What this comes boiled down to is the question whether or not its worth to get the radios checked and re - tuned/aligned and when I do get the fixed does anyone work HF on AM anymore?  Which brings me to another question if anyone knows of a good place to take these radios to get a thorough once-over.  Cosmetically these radios look great and I'd really like to use them but i was just curious about other peoples opinions.  I know i could just buy a yaesu 857d and all my problems would be solved but i decided to go back to school and paying my way through college doesnt leave $900 in the budget.  thanks for the help
-73's
PETE

[N4NYY]

There is a group on 80M that does AM, and most use homebrew tube or boatanchor gear. Nice bunch of guys. I was once having a rag chew on their SSB side of their freq before their net started. When they informed me of it, we told them we would move and they said do not bother, and to just flip the switch to AM, and join them. But we did not, as I have a FT-950.

[WA2CWA]

You'll find AM operating on just about every major band (160, 80, 40, 20, 15, 10, 6, and even 2 meters). If you check the ARRL band plan you'll even find AM calling frequencies listed. And, since AM is "phone" you can find AM operating anywhere phone operation is authorized. Not only is homebrew and vintage equipment used,  you'll also find many AM operators using current state of the art rigs (Yaesu, Kenwood, Icom, Flex, Elecraft, Ten-Tec). Even the FT-950 can operate on AM. I've worked a number of stations using them on AM. The popularity of AM operating has been growing for years. There's even an AM page on the ARRL web site: http://www.arrl.org/am-phone-operating-and-activities

Pete, wa2cwa

[KB4QAA]

Here are some starting points....

http://amfone.net/Amforum/index.php
http://amfone.net/ECSound/
http://www.amwindow.org/index.htm
http://www.ami-west.com/

Gratuitous radio porn:
http://www.radioblvd.com/

[KB5ZSM]

Hey Pete,
         Your question about AM on HF is one you can answer yourself with a decent Short Wave radio. You'll find quite a bit of AM activity, especially on the lower bands. I recommend a lot of listening to the HF bands while you study for your General ticket. It will help you find your niche and learn more about how it all works before you ever pick up that microphone and when you do get to operate in those regions you'll be able to attack them with more confidence.
         As for your Drake equipment, Your radio setup is the same as the first one I ever got to play with many years ago back in high school. It was our school station so I have vary fond memories of that radio I may even buy one someday just for the fun and memories it will bring back. As far as fixing yours up, I think the first thing I would do is buddy up with a local ham who has some boat anchor experience and let him look at it. See what he thinks of its condition. Do NOT just plug it in to see if it works. If it has set for many years with out power, you could do damage to it if you don't bring it up slowly.

Hope this helps & 73s,
Win (KB5ZSM)

[W2WDX]

Two things about AM operation and why it is still popular. Higher fidelity audio and less critical frequency tuning. The latter being less important, the former being the primary reason people still operate on the mode.

The normal operating practice on AM in Amateur Radio is a frequency response in the audio pass-band of about 6-7kHz, compared to about 2.7 kHz (sometimes slightly higher) for SSB operation. This gives a very pleasing sound for normal ragchewing. However AM is very inefficient because of this, which is why SSB is so prevalent especially for DX work. But AM is unbeatable for the local ragchew operation. The extra bandwidth allowed makes for very natural sounding speech and reduces listening fatigue.

The advantage of using older boatanchors is that you can get close to this bandwidth, sometimes, depending on the transmitter. A Yaesu like the 857 still uses its filters so your audio bandwidth is usually limited to under 4kHz, and most times to 3kHz. AM is an afterthought on most modern Japanese/Chinese radios. SDR's like FlexRadio can give significant audio bandwidth approaching that of broadcast standards, albeit this may be a bit broad for amateur use, but not uncommon nor in violation of FCC A3E mode specification.

Actually the designator used in FCC regulations is 8K00A3E which is an 8kHz audio bandwidth. The designator describes the first four characters as "necessary bandwidth required to transmit the desired information". So this is the bandwidth of the information being sent. Most Amateur operators do not use this full bandwidth however even though they can if they wished. BTW, broadcast AM is designated (8K00A3E or even as wide as 20K0A3E (with limits on higher modulated audio frequencies), for reference.

Incidentally, the SSB designator is 3K00J3E. The "J" determines it is a single sideband mode with a 3kHz information bandwidth. Since it is single sideband the radio signal is limited to 3Khz. J3E was brought into Amateur since it reduces congestion within the Amateur bands. The most common in Amateur use is 2K70J3E at 2.7kHz. However this does not preclude that A3E at full bandwidth is not allowed. It should be noted that while these designator appear nowhere in Part 97, they are only referenced there and actually appear in Part 2 Subpart C.

Another fact is there is no mention about "communications quality" for using A3E in Part 97, as is commonly argued. That term is only used in describing certain single sideband emissions "... shall not exceed that of a communications quality A3E emission". In fact, in Part 97 there is no limit mentioned specifically about A3E other than it adhering to emission type standards outlined in other Parts (Part 2 specifically). So in theory one could technically operate at a 20kHz bandwidth as long as you adhere to the standard for that emission type, specifically 20K0A3E, However, in Amateur practice while technically allowable it would simply be rude. So most AM operators have settled into operating using the 8K00A3E emission type on HF bands as good amateur practice.

So as far as "High Fidelity" audio is concerned AM is the way to go in Amateur Radio. Achieving that "Hi-Fi sound and experimentation and developing a station for this goal is what AM operation is all about. Of course, with the virtually "unlimited" bandwidth of the A3E emission type make this possible. If one tries operating true "Hi-Fi" on SSB you may find yourself operating an emission mode not allowable by either the FCC or the ITU. Of course, the true purpose and reasoning for SSB is not fidelity, but instead the goal is efficiency.

John, W2WDX

[K4KYV]

No specific bandwidth limitation is mentioned in the Part 97 rules. The rules vaguely prescribe "good engineering and amateur practice". The FCC intended it that way, in order to allow the amateur the maximum flexibility for experimentation and self-instruction in the radio art.

Therefore, if you decide, for example, to transmit on 160m in the middle of the day, or 75m in the wee hours of the morning when there are likely to be few if any other stations using the band, good amateur and engineering practice might not preclude running hi-fi audio with frequency response up to 10 kHz or more.  No harm done transmitting a "wide" signal when there is no-one else on the band to interfere with.  OTOH, under congested band conditions during prime operating hours, good engineering and amateur practice would suggest limiting the frequency response of the audio modulating the transmitter to 3500 Hz or less.

The same standards would apply equally to AM or SSB. Why would it be less permissible to transmit an audio frequency response up to 5 kHz on SSB, resulting in a total bandwidth of 5 kHz, than to transmit with the same modulation on AM, resulting in a total bandwidth of 10 kHz?

There is an important distinction between the bandwidth of the sidebands resulting from the frequency response of the audio used for modulation, and spurious sideband products resulting from distortion or non-linearity in the transmitter.  Excessive bandwidth due to overmodulation or spurious distortion products is poor amateur and engineering practice, regardless of the actual bandwith of the transmitted signal or the level of band congestion.

The best operating practice would be to use a receiver with variable selectivity or several filters with a variety of bandwidths, and to adjust the audio response of the modulation so that the bandwidth of the transmitted signal is the same as the optimum receiving bandwidth under the given set of band conditions.