- September 13, 2008 at 1:19 am #7158WEAK-AMParticipant
Total posts : 6
I took a look at the 26 MHz DRM local radio broadcasting web site: http://www.26mhz.us. Now, I definitely don’t want to throw cold water on a good idea, but to me, this is really not a good band for local broadcasting at all. As a ham radio operator of many years, I have lived through a number of sunspot cycles. It is entirely possible for very low powered signals to travel thousands of miles on this band with high signal strengths. Before I was a ham, I used to listen to the QRM on CB from all across the U.S. and Latin Amreica. As a ham, I contacted a number of stations in Europe and elsewhere using nothing fancier than a converted CB rig into a quarter wave antenna. And I have to say, from my CB days, I did not think much of the local (non-skip) propagation. Now, a better antenna design will certainly help this situation, but you cannot tell me that there is an antenna made that will entirely cancel out skip. In fact, hams know that you want a low radiation angle for long distance propagation, which is also what you want for good local coverage. So I tend to be skeptical that some kind of esoteric antenna design can magically eliminate this issue.
Add to that the fact that this band is extremely noise prone (primarily ignition noise). Digital transmission is not a cure-all for noise. You might not hear the noise, but you won’t hear the signal either. This is one reason why DTV stations are avoiding the noise-prone low VHF channels like the plague. Any time there is a thunderstorm, my picture freezes or goes blank– and that even happens on UHF if storms are closeby (wonder how the general public is going to like that when they HAVE to watch DTV)?
That said, if someone GAVE us the 26 MHz band and said; “Hey, we can’t figure out to do with this interesting but useless piece of spectrum, so you can have it for local broadcasting!”, then I would agree that it’s better than nothing. But I would prefer someplace higher in the spectrum. For example what about channels 2-4? The DTV’s don’t really want those channels for a number of reasons, and the FCC isn’t sure whether to let unlicensed devices operate on them either, due to concerns about interference with set top boxes. But you could certainly site low power radio stations on those channels such that they wouldn’t interfere, and of course receivers wouldn’t cause any problems. Now to be sure, channels 2-4 are very prone to E-skip in the summertime. I used to talk all over the country and occasionally to South America and Europe on 6 meters, and I also watched TV from stations thousands of miles away on those channels. So nothing’s perfect.
As for DRM, I don’t know much about it but what I’ve heard has generally been positive. I am sure that just about ANYTHING would be better than IBOC; AM or FM. I just HATE IBOC, not to mention that it’s out of the question for most small stations to pay for the license.September 15, 2008 at 4:03 pm #16751givepizzachanceGuest
Total posts : 45366
The first thing you often hear is “I’m a ham” or “I’m a CBer” and “I know that 11 meter signals propagate long distances on low power sometimes. Why, I’ve talked all over the world!” You have to ask how much the person really read the site.
No one who advocates 26 MHz local broadcasting has ever denied the propagation facts. The question on the table is: Does it make a difference? The simulations show that it does not make much of a difference.
Signals propagated from long distances are not likely to overcome the local DRM signal. The listener will still hear their local broadcast just fine even under worst case conditions except at the fringes of the protected contour which will shrink somewhat. But that happens in analog broadcasting too.
The predictions are that the results will be most unlike what most HF ops have experienced. It has to be subjected to additional experiments, instead of just dismissing the idea — “It’s skip, I know it won’t work!”
Experiments have been done, but so far they focused on topics other than station-to-station interference.
> You cannot tell me that there is an antenna made that will entirely cancel out skip.
This is a straw man argument. Nobody has claimed any such perfect antenna. Read the patent on the commercially available 26 MHz antenna for the facts. Entire cancellation of skip is not needed to make it work.
> In fact, hams know that you want a low radiation angle for long distance propagation
Hams still aim their low radiation pattern toward the sky, exactly the opposite of the local broadcaster.
> I tend to be skeptical that some kind of esoteric antenna design can magically eliminate this issue.
The one patented design is not too esoteric but was judged nonobvious enough that the USPTO granted it the patent. Other designs could probably be made as well. But who has claimed magic? Nobody.
The reason for suppressing skywave is that it is just good policy not to waste radiation by sending it to places where it isn’t needed, and because the frequency coordination model assumes that all the stations are using skywave suppression. That is a realistic assumption in a fresh-start band.
> Add to that the fact that this band is extremely noise prone (primarily ignition noise).
The noise in 26 MHz and its effects on DRM transmission have been studied in live tests, in several countries and a variety of environments including some of the world’s largest cities.
The conclusions were favorable. DRM was designed for international broadcasting where the signal travels long distances and is exposed to noise and interference. These characteristics suggested that it might be suitable for local broadcasting even in noisy areas.
> Any time there is a thunderstorm, my picture freezes or goes blank– and that even happens on UHF if storms are closeby
Yep let’s not use UHF for broadcasting. Storms knock it out 😉
> That said, if someone GAVE us the 26 MHz band and said; “Hey, we can’t figure out to do with this interesting but useless piece of spectrum, so you can have it for local broadcasting!”, then I would agree that it’s better than nothing. But I would prefer someplace higher in the spectrum.
That might well happen, in fact both HF and VHF might happen.
It remains to be seen what, if anything, people will want to do with a digital HF band with a regulatory scheme intended to lower entry barriers.
For example, private individuals may not own low power FM stations. FCC rules prohibit it. But should it be forbidden in HF too? To stimulate interest and experimentation, why not let private persons be licensed for their own HF DRM local stations.
Let them try various programming and services. Why stand in their way — and keep the band standing there doing nothing.September 15, 2008 at 4:57 pm #16752WEAK-AMGuest
Total posts : 45366
“The first thing you often hear is “I’m a ham” or “I’m a CBer” and “I know that 11 meter signals propagate long distances on low power sometimes. Why, I’ve talked all over the world!” You have to ask how much the person really read the site.”
That’s certainly a great way to start. FYI, I probably have more years of experience with propagation on the 10/11 meter band than you have been alive. I am sure there are other hams on this board that would be in a similar position. Isn’t is kind of silly to diss hams just because we have experienced what you, apparently, have not?
“The predictions are that the results will be most unlike what most HF ops have experienced. It has to be subjected to additional experiments, instead of just dismissing the idea — “It’s skip, I know it won’t work!”
I did NOT say that “it won’t work”. I called attention to the fact that this is a very noise- and interference prone part of the spectrum. I maintain that it is.
“Hams still aim their low radiation pattern toward the sky, exactly the opposite of the local broadcaster.”
If you believe this, you are a fool. This statement is RUBBISH. Complete BS. Unsupported by any rational thinking person. If you don’t believe me, do your homework. Go to the library and get a copy of the ARRL antenna book, or any of John DeVoldere’s excellent books on antenna design. Or just go and talk to a local amateur radio operator who is a “DX’er”. They will explain it to you.
I am FINE with the idea of using the 26.1 MHz band for local broadcasting. Go ahead if you want to. I just don’t think that the propagation characteristics of the band are well suited to this use.September 15, 2008 at 5:55 pm #16753givepizzachanceGuest
Total posts : 45366
Not trying to get into personal friction here. I appreciate your perspective. It was my first impression too. This is an out of the box idea and is not always received warmly.
The individual who came up with the concept of 26 MHz local DRM is not likely to go around promoting stuff that will ruin his scientific and professional reputation as a PhD physicist and broadcast engineer. Until recently he was spectrum chief at the Voice of America and technical chair of DRM. Those credentials are hard to assail.
> Isn’t is kind of silly to diss hams just because we have experienced what you, apparently, have not?
As a ham for 33 years, I have experienced much propagation at 10m and VHF. It doesn’t necessarily generalize to DRM for local broadcasting at 26 MHz.
That argument is supported by industry standard simulations. It needs RF on the air to see how well it works in practice.
> I called attention to the fact that this is a very noise- and interference prone part of the spectrum. I maintain that it is.
The noise has been quantified. Those who did so concluded that it is not sufficient to prevent DRM from working well. Is it interference prone? It is skip prone on occasion. Propagation and interference are not the same thing of course.
> Hams still aim their low radiation pattern toward the sky, exactly the opposite of the local broadcaster.”
If you believe this, you are a fool. This statement is RUBBISH. Complete BS.
The refraction point is in the sky, not on the ground (some energy does bounce off the ground naturally). But the point of a low radiation angle is to refract from a more distant point in the ionospheric layer. The QRPer is not trying to hit a distant country with groundwave.
In contrast, the broadcaster would use a tower or building mounted antenna that directs most of its energy down (beamtilt). So the DX ham and local station are two different scenarios.
There is NVIS where you aim up and the signal comes down to the coverage area. That has been discussed for local DRM too. But clearly that is not a low radiation angle so it doesn’t apply here.September 15, 2008 at 7:03 pm #16754radio8zGuest
Total posts : 45366
My experience is thus:
On 11 meters when I lived in Montgomery, Oh. just north east of Cincy, there were quite a few of us active on our “chat channel” Reliable day or night communications were routine on DSBAM out to distances of 8 miles or so in a suburban/urban environment using the standard 4 watt transmitters and usually rooftop mounted groundplane antennas. Base to mobile or mobile to mobil was pretty miserable.
On 10 and 15 meters we had an informal meeting “net” and we operated LSB just to be different. It was routine for me, using a 280 watt PEP SSB transmitter to cover the entire Cincinnati area and well into northern Kentucky irrespective of skip conditions. Before sundown it was not unusual to have folks check in from distant states, usually wondering why we were using the lower sideband. Great way to meet people.
My point is that despite the “skipland” problems and sun spot cycle highs, local communication on these bands was effective and this was using analog technology. Digital modulation methods can and do operate at a S/N advantage over traditional analog methods. Though I am not familiar with DRM standards, things such as error detection/correction can go a long way in facilitating communication. This post got to you because of this technology.
A problem to overcome is not technical but rather is the problem David Sarnoff of RCA and Powell Crosley had to overcome: How do you get people to buy the equipment if there is nothing to listen to and how do you justify transmitting programs if there are no listeners? Sarnoff and Crosley attacked this from both ends. Especially Crosley who manufactured radios and operated WLW with great local programming which persisted at least through the 1960s.
Interesting endeavor from all points of view. Hope it works.
NeilSeptember 15, 2008 at 9:21 pm #16756WEAK-AMGuest
Total posts : 45366
“How do you get people to buy the equipment if there is nothing to listen to and how do you justify transmitting programs if there are no listeners?”
This is a BIG problem, as you pointed out. There are several proposals on the table to open up some of the VHF TV spectrum (e.g. channels 5-6) for broadcasting. It will be an uphill battle, but seems to make sense given that Channel 6, at least, is contiguous with the FM broadcast band and is included with that band in other parts of the world.
Rather than going down to 26 MHz, why not set aside a few channels in the new VHF band (or in an adjacent TV channel) for low power/local broadcast operation? According to the Broadcast Maximization Committee proposal, there will be plenty of room for all. This proposal has its own issues, including the one at the beginning of this post. But at least it wouldn’t involve operation in a completely different part of the spectrum.
I have no position on the use of DRM, as I have no experience with it. DRM might be the best technology to use. Hopefully, future software defined radios could handle multiple digital systems, because I doubt that low power radio stations would want or be able to pay for HD.
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