WingNews logo WingNews
top | item 6136201

(no title)

yyao | 12 years ago

Depends on what you want to do. A lot of people think that they need more bandwidth or power to achieve something. This may not necessarily be the case.

QRP guys have crossed continents on less than a watt. I remember from my undergrad days that we've played with band passing the human voice. We managed to get surprisingly good results with 500Hz of bandwidth.

There's a lot of interesting things you can do with more power and more bandwidth. To echo a lot of the other comments made already, if you are doing this without much thought, this is generally frowned upon.

discuss

order

cdjk|12 years ago

Most QRP work is at frequencies less than 30MHz. While 6m might work, tropospheric ducting, sporadic E, etc are touchy enough that adding in QRP operation wouldn't be pleasant. The RF upconverter would help with that, however.

Power is easily solved by an external amplifier.

Increased bandwidth would be nice, but 20MHz is plenty. While you might need that for microwave experiments (wifi, gsm, etc, and spread-spectrum experiments), the big advantage of the bandwidth is being able to listen in to everything at once, and see where signals are at a glance, without tuning through frequencies. Being able to glance at an entire band, and immediately see where QSOs are happening is pretty cool. Or you could record all of the FM broadcast spectrum, and decode it at your leisure later. That's not too practical, but is pretty cool. And 20Mhz is wider than every ham band 2m and lower.

And 500 MHz isn't quite enough for voice - SSB is generally 2.3 - 3 kHz. 300-500 Hz is ideal for CW (morse code), and digital modes can use even less.

VLM|12 years ago

"Most QRP work is at frequencies less than 30MHz. While 6m might work, tropospheric ducting, sporadic E, etc are touchy enough that adding in QRP operation wouldn't be pleasant."

Not my experience at all. I have been wallpapering my radio room with 1st place wins as a QRP entrant in the ARRL 10M contest in December for a couple years.

During a Es opening my 5 watts might only be S9+10dB whereas a guy with a 1500 watt linear would be S9+30dB so you can see why its not much of an issue.

Before I got a modest brick for 6M it was the same deal every July and December. I'd have 5 watts out and work guys 1000 miles away who had signals S9+20dB and I'm sure I was "merely" S9 or so on their side.

Another thing is the ops on 6M are gentlemen, by self selection this is not 80M or 20M sideband. They're glad to work a "weak" signal and don't turn down their RF gain or whatever those HF ops do.

When propagation smiles on you, power out doesn't matter. When it doesn't, well you're screwed even if you have illegal levels of power.

I live in a part of the country where the 1000 mile Es donut covers pretty much all the sand states. So I have a lot of Grids! I near got DXCC during just one VHF contest in the spring in just one day!

yyao|12 years ago

> 500 MHz isn't quite enough for voice

Thats what I thought. We had a few teams look at ways to carry human voice with less BW in a sensory communications course. The winning team did it with 500Hz. I remember it clearly. There was a stunned murmur during their project presentation when they announced their results.

I don't remember the exact numbers, but the gist of it was, they applied 2 bandpass filters, one on a lower frequency range and the other on a higher frequency range. Both passbands were 250Hz wide. They combined the two signals together as a 500Hz signal. The pass bands were seperated by 500Hz or 1kHz IIRC. So pretty much they kept the lower and higher frequencies and threw away the rest. The result was pretty good. Human languages have a lot of redundancy in information and the quality was good enough for general conversation. It was comparable to what you have on a cell phone.