New ARRL Bandplan Technical and Regulatory Concern

Mark,

Keep in mind with PSK31 you will have to have a pretty narrow bandwidth on your spectrum analyzer to see the intermod products. If your center freq is 28,000,100, the 3rd order products will be at 28,000,085 and 28,000,145. So a 100 or 200 Hz bandwidth is all that is needed. However, if your analyzer puts markers at the proper point, you already know this, so pardon me if I am just stating the obvious.

Jim
WA0LYK

 

Mark,

Rather than risking burning up attenuators, I would see what you get by drooping some wire over a dummy load. You won't get absolute quantities shown on the analyzer as you would with a direct connection, but the relative levels should be accurate.

Also, it would be fun to see how the amp reacts to an SWR mismatch if any of your antennas have a slightly high SWR, like at the band edges.

Thanks,

Jim
WA0LYK

 

Jim,

I found a free program that will let my soundcard do two tones and tried a two tone test last night. The preliminary results on 28 MHz were close to what the ARRL lab had published for the iC-746. It seems to have a lot to do with the power output of the radio, but it could also have something to do with the level of the audio. I am not sure how much of the IMD was generated in the sound card, so if I have some time today, I will evaluate the quality of the two tones comming out of the sound card.

I said I had used psk31 in a previous post, I actually used PSK63 to get a little more tone separation, but looks to be 63 Hz between tones. Maybe Skip KH6TY can tell us more about the frequency separation when using PSK63.

73,

Mark N5RFX

 

Mark,

In PSK63, everything is just twice that of PSK31.

Skip

 

My soundcard is not a good two tone generator. The IMD from the sound card is -32Db. I am looking at building the 2 tone test generator that the ARRL uses.

73,

Mark N5RFX

 

NEWS FLASH: FCC on November 24 dismissed a petition for regulating SSB and AM transmitter bandwidths to 2.8 and 5.6 kHz respectively (RM-10740). In the ruling, FCC reaffirmed the appropriateness of unspecified emission bandwidths citing among other things the experimental nature of the amateur service.

It might be wise for ARRL to re-think their idea of asking for emission bandwidth restrictions on amateur transmitters.

73 Mike

 

Mark, it might be simpler just to get a Soundblaster card. I get as low as -42 db IMD as measured on a low-level PSK31 20m signal generated with my Soundblaster AWE32 soundcard, and received with a Soundblaster 16 soundcard, and this is during clean, actual over-the-air transmission and reception.

73, Skip KH6TY

 

Mark,

Catching up on the thread (which has drifted WAY down on the list). Yor point about necessary versus occupied bandwidth is possibly one way for ARRL to fix their proposal (I still have other problems with it). If what was specified was an ITU designator (which uses necessary bandwidth) and the "best amateur practices" was still left in the rules, then we wouldn't have to worry about measuring occupied bandwidth at the -26 dB points (which by the way, is required by the Canadian regs - they seem to spec occupied BW).

I suspect that a modern rig, generating AM by injecting carrier into a DSB process, might be able to meet the 6 kHz definition. I suspect that many (most?) old AM rigs (class C final with a classic plate modulator) will definitely fail occupied bandwidth, and without rework of the modulator, probably wouldn't be able to *meet* necessary bandwidth. While the necessary bandwidth of AM by *definition* might be 6 kHz, this assumes that the equations used to define it have some relationship to the hardware - thus it works for modern, ostensibly SSB rigs with 300-3000 Hz audio passbands, but not necessarily for old (commercial or homebrew) plate modulated rigs where the modulator was typically designed for wider (especially in the case of recycled AM radio station rigs, which were designed to support music, operating on 160 meters). While 6kHz may guarantee that "rich" sound of full bass (only an extra 600 Hz), it still won't help most classic AM operators.

Your point about spurious emissions reveals some problems with the way Part 97 is constructed. There are places where "bandwidth" (refering to the -26 dB width), "occupied bandwidth" (same definition), and "necessary bandwidth" (the *ideal* bandwiddth) are used in rule parts, and to my reading, generate a conflict at times. This does not occur in all FCC rule parts as spurious emissions are usually defined as those that are beyond the out-of-band-emissions (OOBE) - typically the -26 dB point, but in some rules parts different values are chosen.

One of the problems I have with the bandwidth proposal is that even if necessary bandwidth is used, 500 Hz is not enough for 300 baud packet (650-700 Hz is more likely). I like your 1000 Hz proposal. Others have pointed out that CW might not even make 200 Hz, I disagree generally with those who are worried about this since the ARRL calculation was based on 60 WPM, and Part 97 still calls for avoiding keyclicks on adjacent frequencies. Some rigs (especially on inital chacter in semi/break-in ) certainly have a problem, and you can always over-drive an amp, but if you have bad clicks, people will let you know (especially if they live nearby!). Again the necessary bandwidth would fix this. My problem with Pactor III is I think it is illegal in the current rules framework, and I don't even know if "publishing" it will fix my other problem with it if the owners ever try to enforce patent rights down to individuals, especially those that might just write articles - not even build hardware/software.

I'm not sure I have followed your argument here (or in 04-104) with regard to the funny fax mode in MixW (I didn't even know it switched modes to send photos - thought it just sent digital imagery). If we just got the FCC to extend §97.307 (f) (8) to HF, wouldn't that fix things, rather than trying to let one mode through at a time. Like you said, they all end up "looking" the same.

What you need for your 100 watt testing is a coupler - something like the Breune bridge used in most power meters. You only want a signal thats 20 or 30 dB below your desired level to start with, and then attenuate more! And old trick (that is frequency sensitive, not like the Breune) is to take a short piece of coax with connectors at both ends, and the outer rubber insulation removed. Carefully thread a piece of magnet wire under the braid for a few inches. Strip and solder one end of the magnet wire to the braid, and take the other end off to a connector and 50 ohm termination. Coupling increases with frequency (so much more out on 10 meters than 80), but since all your measurements are relative to the desired in-band signal, this won't be a problem, since it sounds like your Anritsu will automatically measure from the local peak down to whatever spur you're examining.

 

Mike,

Thanks for all of the info. I have ordered a Bird 4431 which is a model 43 with a variable sampling port. I used one of these a several years ago to do some testing on 300W 900MHz transmitters. We were bringing the input to a modulation domain analyzer. We added attenuation to the sampling port and it worked very well. I think it will work very well for this application too. I have always wanted one of these so that I could use my bench scope as a mod scope.

73,

Mark N5RFX

 

Hi Skip!

I am was using a sound blaster USB sound device. When I use PSK31, 63 or 125 with this device to another soundcard I get -50dB or so IMD as reported by MixW. When I use the NCH Tone generator with the RightMark audio analyzer I get -32 dB. Then I used HamAnalyzer audio spectrum analyzer and came up with -32 dB again. I am starting to think that a two tone test is a very severe test. I will work something out.

73,
Mark N5RFX

 

n5rfx: "I am starting to think that a two tone test is a very severe test. I will work something out."

Mark,

A two-tone test IS a very severe test. The input tones and their mixing must be very clean or it can bias the test big-time.

All transmitters have IMD. It can be generated in every stage of the transmitter. IMD is generated any time non-linear operation is involved in any stage. I'm sure you have seen the operating curves of transistors and FET's. Unless the system design is such that the maximum operating points are well within the middle points of the operating system, IMD can occur even with so-called class A operation.

tim ab0wr

 

Yes it is the equal amplitude part that really makes it tough. If either of the two tones is reduced by 1dB there is a 3 dB drop in the IMD. I thought this would be the case. In my line of work that has always been the rule of thumb at sites. I think all of my soundcards are not going to be adequate for this test. I need better isolation between the two audio tones.

So this brings up another point, with a complex waveform the probablility of having two equal amplitude tones for a long duration is very small. This may be why the IMD is not regulated in amateur equipment, but what I don't understand is why IMD is not considered a spurious emission?

73,

Mark N5RFX

73,

Mark N5RFX

 

mark: "but what I don't understand is why IMD is not considered a spurious emission?"

Who says it isn't a spurious emission? I think according to most standards bodies, it actually is a spurious emission. I think the problem is the test definitions the ARRL uses. When they measure "spurious emissions" and "imd" they are both actually measuring spurious emissions, per se, they are just measuring different kinds of spurious emissions. The "spurious emission" test should actually be called something else like "non-imd spurious emission test" (smile) or "single-tone spurious emission test".

tim ab0wr

 

Mark,

Have you just tried calling CQ into the microphone or some other combinations to see what that does, especially if the mic gain is set where the ALC tops out? With compression on would be interested also.

Jim
WA0LYK

 

Just to tie up one loose end on this thread, I received my wattmeter with the sampling port today, and that has made measurement at higher power possible. My soundcards just produce too much IMD on their own to use them for a two-tone test. I will have to build a 2-tone oscillator I think. Mouser has all of the parts. Anyway what I did do was the random noise and a voice test.

For the voice test I first set up the rig with no compression, mic gain at 10 o'clock and rf gain max. This gave me 50 watts PEP 3 watts average and no alc. The specan reported OBW <= 3Khz. The next test was with the mic gain max and the compression max. The ALC was within the scale. OBW<= 3KHz. I then changed the specan to hold the peaks. When I did that the OBW when using max power and compression went as high as 7 KHz.

For the random noise test I used a General Radio 1381 with 5kHz bandwidth and 2 sigma clipping. The first test was with the mic gain at 10 o'clock and 50 watts pep output and average power 20 watts. The OBW was <=4 KHz. I then upped the power to 100 watts, alc in scale, and average power 50 watts. OBW <= 6kHz.

The frequency used was 28300Khz. This was the band that had the worst IM performance in the ARRL tests on this rig (IC-746).

I can see that with a two tone test the IM products will have a 100% duty cycle. With random noise and voice, the IM products are there, but have a shorter duty cycle.

73,

Mark N5RFX