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Bluetooth STL follow up

Here's a follow up to our earlier discussion on Bluetooth studio to transmitter (STL) links. After some testing on several different Bluetooth devices, your Low Power Radio blog discovered some "Wows" and some "Ouch facctors."  Here's a short summary.
Ideal response curve
     Wows - The number one wow outcome was range.  Most of the units tested easily met the thirty foot promised range and, with the exception of masonry, weren't greatly impacted by structures.
     Number two was connectivity. With only a few exceptions noted below, once the connection was established the Bluetooth STL was quite reliable.
Real world response curve
     Ouch factors - the units tested delivered three distinct rude surprises and the first was the undocumented features a few of the units offered.
     Some of the units tested provided internal and cell phone battery saving features that put the Bluetooth unit in sleep mode after a short absence of audio signal.
    Worse, some of these provided signal tones to alert the user to the sleep and wake states of the Bluetooth.
     When in the audio chain, these tones came through at an ear-splitting level and the noises emanated by the transmitter sounded like bim - pew - thunk every time the chip went in and out of sleep mode.
     The second major ouch factor was the frequency response curve or, rather, the compatibility of the Bluetooth response curve with the transmitter audio sensitivity.
     Our transmitters tend to have a fairly narrow window, with FM transmitters usually in the area of 100 Hz to 10,000 Hz and AM transmitters an abysmal 500 Hz to 8,000 Hz.  FM transmitters usually offer a pre-emphasis circuit to help the top end and a compressor can help the bottom in both AM and FM.
     Audio chain components are usually compatible with the AM or FM audio bandwidth but a Bluetooth STL ouch occurs when the audio chip adds another curve to the picture.
     One of the units tested had so much bottom that the result was impossibly muddy, another was too strong in midrange and a third was hopelessly shrill.
     The third and perhaps most frustrating ouch factor was the lack of transparency in specs and chipsets.  Our faithful readers might be wondering why no brands or models are mentioned in this report.  The reason for that is that testing showed that brands and models are not dependable predictors of the chipsets used and therefore not predictive of success or failure.
     Bluetooth audio devices are manufactured in batches using inexpensive chipsets built by offshore factories and the same make and model, purchased at different times, will have different chipsets.  There seems to be no way to make a dependable recommendation.
     Instead, the recommendation is to purchase your Bluetooth STL components from a vendor with a liberal return policy.  If you get a unit with an intolerable bim-pew-thunk or a a set with a response curve that's a poor match for your transmitter audio, send it back and try another.

Electronic goodies galore

Here are some links for those interested in electronic goodies, kits to build electronic devices, new electronic hardware, overstock electronic components and equipment, new old stock, commercial oddities and surplus in the electronics realm.
    Unlike some of these aggregations, it's mostly audio and RF electronics rather than computer hardware. A great combination of lists that a number of authors have busted butt to create.
    It's a situation where a blogger thinks to himself "I could steal all of these links or I could just link to the author's pages."
     Unfortunately, sometimes just linking turns put to be a bad idea, like in the case of the Italian guy's MW schematics, now apparently gone.  I really wish I had stolen those...
     So, on the topic of stealing, the character Frank Burns once said on the TV show M.A.S.H. "When you steal something, never try to return it."  I guess I'll add "If you ever want to steal something and then you decide to take the high road, you're probably going to regret it later."
     In the spirit of hoping I don't regret this...      Someday, maybe Jeff Bezos will have all of our needs on Amazon. Until then, we can use these lists.

Phono oscillators - a Knight in shining (blue) armor

Click the pic for a full color image tour
One of the coolest things about what's left of the internet is that, at least for now, nearly anyone passionate enough to spend a few hours hunched over the keyboard can promote the object of their affection to the world.
     A delightful example of this publishing freedom (cherish it!) is the growing family of tribute pages to a little know historical technology called the phono oscillator.
     Strange as it might seem to a generation accustomed to getting one of the most powerful computing platforms ever known at no charge in exchange for a two year contract, technology used to be really expensive.
     Phono oscillators were a work around to get double duty from the large investment mid-20th century families made in then-expensive radio radio receivers.
     For the relatively low cost of a phono oscillator, your home record collection could be heard in the stunning high fidelity sound provided by your console set.
     Here's a stroll through some of what was found on the web: - Knight-Kit Electronics presents the Knight Kit Broadcaster Fan Page dedicated to the Knight-Kit Broadcaster. Be sure to check the links throughout the site, I'm pretty sure I like that coffee mug.... kit home broadcasters - The Knight Wireless Broadcaster-Amplifier takes only a few hours to build... Broadcaster - Experiences with the Knight Radio Broadcaster. Radio stuff/Knight - Original assembly manual. - Memories from users of the Knight Broadcaster. - The esteemed and far better organized page on Phono oscillators. from the home - Welcome to the world of home wireless broadcasting!. SMECC's Phono Oscillator page. - How many of our readers ever wanted to be a deejay or operate his or her own transmitter to play music? - The competing Lafayette LA-23 / KT-195 Amp & Wireless Broadcaster. - The oscillator on this page is based on the 1939 Zenith S-7000 series. Stereo XMTR - Bob Weaver's three tube C-QuAM Stereo Transmitter. - Needs parts for your tube-ular ventures? Try Antique Electronic Supply - AES!

     Hopefully, this look back to a more technologically sparse era will help us remember how fortunate we are to be right here, right now.

A rather meager webring

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