Sidebar Links Reorganization

I’ve re-organized the sidebar links to sort them into categories. Because my own interests in the Radio, Broadcasting, and Wireless field is so broad, the collection of links was likewise broad. I’ve created the following categories:

  • Amateur Radio and DX
  • Broadcast Blogs, News, and Trends
  • Broadcast Equipment
  • Broadcast History
  • Broadcast Technology
  • Radio and TV Stations
  • References
  • Unlicensed Broadcasting
  • Vintage Radio
  • Wireless Data Transmission

Amateur Radio and DX primarily deals with Amateur (HAM) radio and the hobby of listening to distant stations.

Broadcast Blogs, News, and Trends, primarily deals with information sources pertaining to current events in the broadcast field, anything from personal blogs to industry news to scathing editorials. Sites that are more geared towards the technology and theory behind it are in a separate Broadcast Technology section.

Broadcast Equipment is for sites primarily selling broadcast equipment.

Broadcast History is for sites primarily concerned with the history of radio and television broadcasting.

Radio and TV station consists of web sites for operating radio and television stations. Note that unlicensed stations will be placed in the Unlicensed Broadcasting category.

References is sites which primarily consist of reference data, radio station databases, etc.

Unlicensed Broadcasting consists of sites which primarily relate to unlicensed broadcast operations. These may be part 15 stations, bootleg or pirate radio stations, or any other form of broadcast without a license.

Vintage Radio consists of sites which have information on or sell vintage radio equipment. There is some overlap with the Broadcast History category as many of these sites selling vintage equipment also have some history on them, and some history sites will have minor sales functions. If the primary activity of the site seems to be geared towards sale of vintage equipment or if the emphasis is on the equipment and not the broader history, it will be listed here.

abdx.org

I added a link for abdx.org. They are a group of radio enthusiasts interested in American broadcast DXing. This is a hobby I used to be fairly heavily involved in, particularly TV DXing. Unfortunately, most of the activity seems to be on a Yahoo mail list rather than on the website. However, there are some cool tower pictures including one of a tower downed after a storm.

Analog AM/FM Cutoff

An article in ElectronicsWeekly.com entitled, “AM Radio Broadcasts Could End In Two Years“, I find very troubling.

I understand the governments desire to end analog TV service. All the digital channels have been moved to UHF and ceasing VHF broadcasts will free up that spectrum so they can auction it off to the highest bidder. What ever happened to governing the airwaves to serve the public interest?

I don’t understand the rush to shutdown analog AM/FM transmission since the digital counterpart occupies the same frequencies. I also hate to see all those old AM furniture radios no longer functional.

I don’t like the Ibiquity HD radio system for AM at all. FM, so-so, it’s probably an improvement over analog subcarriers. The AM Ibiquity HD radio system is a gross waste of bandwidth. Better quality audio could be fit into an existing spectral footprint.

They are trying to stick us with a system that is incompatible with the rest of the world to limit our exposure to news and opinion from the rest of the world while at the same time edging out smaller broadcasters so that only a handful of mega-corporations remain. We’ve already had a sample of “Fair and Balanced”, and that’s what we’re going to get more of if we allow this to happen.

There is no reason to force a change over. If the economics favor it, stations will switch on their own. I do think that stations on AM should either broadcast analog or digital, not waste bandwidth with hybrid systems, but I do not think the entire band should be mandated to change. A system, such as I proposed, which would fit in the same spectral foot print would allow stations to switch as they felt it was economically beneficial to do so without impacting adjacent stations.

A few analog stations would remain to service those old radios. The biggest thing I don’t like about Ibiquitys’ system is that it uses three channels for audio with “fake” highs when it could fit audio with “real” highs into one channel if it got away from proprietary and non-compatible standards and used open and compatible standards.

I’d urge people write your congress critters and tell them the FCC needs to be returned to governing the airwaves in the publics interest, not in the NAB’s, not in Ibiquitys’ interests. You can write the FCC too but given that they are owned by corporate interest there doesn’t seem to be much chance at persuading them directly.

Undestanding Cell Phone Tower Health Risks

There is a lot of paranoia surrounding cell towers s and possibly human health risks. What is important to understand is that radio frequency field intensity is related to the inverse of the distance squared. The exposure that you get from being in the vicinity of a cell tower is hundreds of times lower than the exposure you get using a cell phone.

The only exception to this might be in a situation were cell phone antennas are operated on top of a roof and people are allowed access to that roof top so you can get right up close to the antennas.

Some early studies of cell phone usage showed some adverse health effects, a slightly increased risk of brain tumors and cataracts among them. However, the largest and most recent study did not show any increased risk.

This isn’t to discredit earlier studies however. The earliest cellular handsets operated at power levels up to four watts. Without any external input your brain normally produces about 12-25 watts of heat. An additional 4 watts is a significant heat load and it’s not heat that is distributed evenly but rather concentrated near the antenna. So it is extremely likely that there were significant health risks with these phones.

The next generation cut that power to 1 watt maximum. Still enough for mild thermal effects and possibly some marginally increased risks.

The next generation after that which still operated at 900 Mhz had a maximum transmit level of about 250 milliwatts, a quarter of a watt. This is really approaching a power level where thermal effects are becoming insignificant. These phones only operate at maximum power if they are in a poor signal area.

The very latest generation operating at 1.8 GHz uses a maximum power of 100 milliwatts and will step down to as little as 1 milliwatt if the signal level is good. This is not enough to cause significant thermal heating and is safe.

The field strength you are subject to from cell towers is a small percentage of the field strength you are subject to using even one of these modern phones. They represent no threat.

For cell phone users, more towers reduces your exposure because your modern cell phone steps down it’s power when the signal is strong. If you’re a few hundred yards from a cell tower, that cell tower doesn’t require that your phone transmit at a high power level for it to receive it. If you are several miles, then your phone must transmit at a higher, but still safe, power level.

AM Bandwidth and Digital Radio

A recent commentary article in Radio World addresses the issue of AM bandwidth. I believe there are hidden agendas.

In the North America, AM stations are assigned to frequencies from 530 KHz to 1700 KHz in 10 KHz increments (other parts of the world use 9 KHz increments). When a radio signal is amplitude modulated, sidebands are generated at the carrier frequency+modulating frequency and the carrier frequency-modulating frequency. For example, if a station at 1000 KHz modulates the transmitter with a 1 KHz tone, it will create sideband frequencies at 999 KHz and 1001 KHz.

Since stations are spaced 10 KHz apart, any modulation frequency in excess of 5 KHz results in sideband products spilling over into the adjacent channels spectrum. Years ago, the audio modulating AM transmitters was rolled off after 5 KHz to prevent interference with adjacent channels.

FM, with it’s capability of reproducing audio frequencies up to 15 KHz, began to compete with AM. The fidelity of AM became more important. Stations were allowed to modulate up to 7.5 KHz improving the fidelity. This did cause some interference to adjacent channels but normal wideband receivers were not selective enough to separate adjacent channels. Limiting modulation to 7.5 KHz still meant the adjacent channels spectrum was clean out to 2.5 KHz from it’s carrier allowing narrow bandwidth receivers to receive an adjacent channel without interference.

FM continued to gain market share. AM stations were allowed to go up to 10 KHz which means they’d splatter over an entire sideband of an adjacent channel resulting in objectionable interference even for a listener with a narrow bandwidth receiver. AM stations even boosted high frequencies to compensate for high frequency roll-off in receivers.

Recently, the NRSC performed limited listening test using only three receivers and thirty subjects. Adjacent channel interference used simulated noise instead of real program material. Simulated noise made it possible to bias the tests towards a listener preference for constrained bandwidth by exaggerating the resulting interference. These tests determined that there was no advantage to a 10 KHz bandwidth. I guess that’s why broadcasters pushed to go to 10 KHz from 7.5 KHz.

HD Radio, iBiquity’s digital radio system for AM, utilizes spectrum from either 5 or 7.5 KHz to 15 KHz from the carrier, depending upon mode. To use this system you must constrain the audio bandwidth of analog audio. Ibiquity’s system only achieves a data rate of 36 Kb/s with 7.5 KHz – 15 Khz and 56 Kb/s with 5 KHz – 15 KHz. This is very poor use of precious AM broadcast spectrum, the total bandwidth utilized by an hybrid iBiquity digital AM signal is 30 KHz.

The HDC codec is a multi-streaming version of HEACC, which is AAC+ with SBR, the same Codec used for XM satellite. I’ve read in the XM blogs, 48Kb/s provides high quality encoding, at 40KB/s the definition is lost, at 32Kb/s quality is seriously impaired.

SBR, spectral band replication, reduces encoding bandwidth by discarding high frequency audio detail. At the decoding end it replicates the lower frequency spectrum to replace the lost high frequencies. Most high frequency program material is harmonically related to lower frequencies. The problem is that the exact nature of the harmonic content varies greatly in music from instrument to instrument. Flute producing almost a pure sine wave with almost no harmonic content. A brass horn or stringed instrument is rich in harmonics. The decay envelope for instruments is not the same for harmonics as for the fundamental.

Ogg Vorbis encodes good quality stereo at 45 Kb/s, the whole spectrum, no need for SBR. It is an open format and iBiquity can not extract licensing fees.

DRM, Digital Radio Mondale, is able to achieve a 30 Kb/s in a 9 Khz spectral space using using QAM64 modulation of the CODFM carriers. 15 KHz of spectrum would yield 50 Kb/s which would suffice for full spectrum Ogg Vorbis stereo encoding. The DRM format is used for LW, MW, and SW digitial broadcasts in the rest of the world.

I am all for digital radio, just not 30 KHz wide inefficient hybrid proprietary digital radio with garbage audio . We can have high quality audio in half the bandwidth with a non-proprietary encoding scheme. The F.C.C. was mandated with the task of regulating the public airwaves in the publics interest. The AM version of HD radio is not in the public interest. A DRM digital stream and Ogg Vorbis encoding would utilize bandwidth more efficiently and provide higher quality audio. Receivers and transmitting hardware would be less expensive since no royalties would need be paid to iBiquity.

RSS Feed

I’ve added an RSS Feed to this blog so those of you who wish to follow it with an RSS News reader or add it to your website or headlines to your blog can do so.

AM Sound

Perry Lind made the comment that the old Westinghouse Electric transmitter sounded better than the modern transmitters, I’ve got mixed feelings. The old high-level plate modulated transmitters did sound good if they were well engineered and maintained within the limits of their capabilities. Modulation transformers and reactors resulted in bounce and tilt and limited the modulation that could be obtained to lower levels than it otherwise could be without overmodulating negative peaks.

Some of the other systems like the RCA AmpliPhase or CCA’s Doherty modulation sounded ok if everything was perfectly tuned and tweaked and in good order but were difficult to maintain in that state. The ampliphase system was kind of icky in that the relationship between phase angle and power output wasn’t linear and I don’t think predistorting the audio to compensate did so adequately.

One problem with any of the old tube transmitters is that tubes don’t just run perfect until they fail, they gradually lose their ability to emit current from the cathodes efficiently and high power tubes are expensive so there was a reluctance to replace them until they were really sick. This would cause the RF finals to be incapable of handling positive peaks linearly or the modulator tubes would get weak and become incapable of creating enough power to modulate the transmitter completely.

I know the CCA’s were cable of high modulation. I don’t know what KHHO (formerly KTAC) is using these days, but back in the last 70′s they had a CCA beast of some sort and I remember being down there and looking at the modulation monitor, a unit with a couple of LEDS when peaks exceeded the threshold set on a couple of calibrated dials. The positive dial was calibrated up to 133% but the knob actually turned physically past that point (and was), and the LED was for the most part continuously on. And actually it didn’t sound that bad given the degree of audio crunching that was taking place.

The Harris pulse width modulation (class D) transmitters and later the digital modulation transmitters (which essentially is equivalent to pulse with modulation using the RF stage as the pulse width modulator stage at the carrier frequency) also sounded good and both were capable of heavy modulation.

The tendency of transistors to work until they don’t and the fact that they’re operating in a switched mode making linearity a non-issue, means that the audio quality and modulation capability doesn’t gradually degrade as the tubes age. The efficiencies are also high, which perhaps if you’re in a cold region of the country in the winter and not paying the power bills is not such a good thing.

I think what sounds not so good with many of todays stations is the audio processing and audio sources that are used. Take bad audio, run it through an audio chain that stomps it entirely flat, and no transmitter is going to sound good.

blatherWatch

I added a link to blatherWatch blog on the sidebar because they’re willing to, “listen to talk radio so I don’t have to”. With the content of today’s talk radio, at least in this region, that’s some real self-sacrificing going on over there.

I used to enjoy talk radio many decades ago. I loved to stay up late and listen to KGO 810 from San Francisco. That was back when there were clear channels and before KGNW 820 was allowed to broadcast at night.

Talk radio today isn’t like talk radio then. Now it’s talk propaganda. No longer are all sides of a topic discussed. Now you have your choice of about a dozen right-wing wacko stations and one left-wing wacko station. Neither camp will allow an issue to be examined from all sides or in depth. They no longer encourage people to think, instead, they encourage you to allow them to do your thinking for you.

My thinking may not be the best but at least it’s mine and I prefer that it stay that way. For the most part then I’ll allow blatherWatch to listen to talk radio so I don’t have to.

Frank’s Electron Tube Pages

Frank’s Electron tube pages is a great resource for those who are still enjoy the warmth and glow of vacuum tube technology.

On this site you will find PDF data sheets for just about every tube known to man including hi-power transmitter tubes. There are also links to sites with foreign tube data sheets and substitution guides.

I’ve added a link to the sidebar so that it will remain available even when this post is long buried.