Messages

766

General Radio Discussion / Re: Anyone have a spare 50Kw SW Transmitter ??

« on: December 15, 2017, 2256 UTC »

pfft... A Harris of that vintage, I'm surprised it lasted that long.

They are indeed lucky it didn't take the building.  A lot of early MW-5's would do similar, and take the building with them.

+-RH

767

The RF Workbench / Re: Naughty Idea

« on: December 15, 2017, 1557 UTC »

Digikey, Mouser, Jameco all have 48V supplies from 25-2.5KW.  My current prototype runs on 3 48V supplies turned up to 55V and wired in series to get 165VDC for the modulator.

+-RH

768

Equipment / Re: Procaster AM Transmitter Review

« on: December 14, 2017, 2122 UTC »

Part 15 certification is not that expensive, and we all know how effective the FCC is at policing that anyway.  In the end I believe the cost to be a combination of development, and a vendor that believes they have a corner of the market and can name their price.  I am willing to pay extra for quality, but anymore that seems money wasted.

+-RH

769

North American Shortwave Pirate / Re: Clever Name Radio 6940 USB 2151 UTC 13 Dec 2017

« on: December 13, 2017, 2154 UTC »

6939.99 KHz USB S9 on peaks.

2150z a mashup of James Brown Led Zepplin's 'Whole Lotta Love'
2154z 'Rock and Roll Music'
2156z UNID hip hop tune with Carribean elements.
2157z Previous song cut off abruptly, then into Butthole Surfers 'Pepper'  Clever Name Radio ID over top of intro ramp of song.
2202z a few random pieces of several songs, into a Cheech and Chong bit about Santa Clause.
2209z Crystal Method 'The Name of The Game'
2210z UNID dubstep track with old movie quotes throughout.  Up to S9+10, fades becoming more pronounced.
2214z Clever name Radio ID, into Prodigy 'Breathe', one of my old fav's
2221z ID, into Godsmack 'I Stand alone'
2225z ID, into Breaking Benjamin 'Cold'
2226z Off?  Nope, ID, then a few clips of songs, then Rage Against The Machine 'Sleep now In The Fire'
2232z Sounds like Prodigy, but can't remember the song title.
2237z ID, then Jerry Reed 'Amos Moses'
2241z Jerry Reed 'She Got The Goldmine'
2243z Ford truck commercial, then Pearl Jam 'Animal'
2246z More Pearl Jam.
2320z Request ID, then into Twenty One Pilots.

Requests eh?  How about some Tool?

2322z Tool 'Schism' THANK YOU!!  It was a cold dark night when I first heard this song and my life was forever changed.  I still get chills when I hear this
2329z Disturbed 'Droppin' Plates'
2333z Disturbed 'Bodies' clip then Free 'All Right Now' then Heart 'Barracuda'
2335z Icona Pop 'I Love it'...I don't, lol
2337z Request ID, then Korn 'Got The Life'...an old fav

The Prof' wants to hear some Zappa.
2344z Frank Zappa with a piece from 'Joe's Garage' Thank You!!
2347z Filter 'Hey Man Nice Shot'
2355z Jon Lajoie 'Everyday Normal Guy'

Thanks for the show and requests CNR, gotta run!

+-RH

770

The RF Workbench / Re: Naughty Idea

« on: December 13, 2017, 1902 UTC »

Basically what this guy did...

http://amfone.net/Amforum/index.php?action=dlattach;topic=30798.0;attach=31360

Class D full bridge RF amp fed by a torroidal power transformer and a high power audio amp.

+-RH

771

General Radio Discussion / Re: WCAZ NOTICE OF UNLICENSED OPERATION

« on: December 13, 2017, 0121 UTC »

Probably a few grand...plus fees.  They LOVE fees

+-RH

772

Equipment / Re: Procaster AM Transmitter Review

« on: December 12, 2017, 1648 UTC »

Agreed, for that much money I could probably build a 250W or better rackmount stereo transmitter.  I do understand that a lot of folks want plug and play, however.

+-RH

773

The RF Workbench / Re: Any DDS 200 watt AM Transmitters or kits

« on: December 11, 2017, 0414 UTC »

That's true.  My old amp needed about 100 watts PEP to get full power.

+-RH

774

The RF Workbench / Re: Any DDS 200 watt AM Transmitters or kits

« on: December 10, 2017, 2309 UTC »

Why bother with linears when you can have a TX that is a lot more efficient and will have lower distortion?

Did I mention lighter too?

Yes, they should play nice provided your amp provides a flat and non-reactive load.

+-RH

775

The RF Workbench / Re: AM stereo Generator designs plus 300 watt Digital RF

« on: December 09, 2017, 1919 UTC »

With the exception of Nautel's NX series, all modern stereo capable transmitters require a fairly complicated alignment process using single channel modulated tones, a reference demodulator, and a scope.

The original Motorola equipment was usually installed and aligned by a field service engineer, not the station chief.  When 'Moto started allowing third parties to license and manufacture equipment, all that changed.  To my knowledge, the only gear you can still buy is made Broadcast Electronics, or Delta Electronics.  BE for a time made a modulation monitor for C-QUAM, I've only ever seen one in the field.  I have seen a few original Motorola exciters and monitors out there too.  Delta will still sell a stereo modulation monitor and exciter, but they are the last to do so.  BE offers a stereo generator board for their A and E series transmitters.  Motorola got out of the broadcast end of the business in the late 80's or early 90's.

The options are not cheap.  The last time I priced a mod monitor from Delta, it was around $4K.

+-RH

776

The RF Workbench / Re: AM stereo Generator designs plus 300 watt Digital RF

« on: December 09, 2017, 0205 UTC »

The large IC is a PLL synthesizer used to generate the carrier frequency, most likely times 4.  In a conventional design, this would be followed by a quadrature divider, usually realized as a two stage johnson divider feeding two balanced modulator stages, one for I and one for Q.  The I stage has a dc bias applied to the modulating input to created the 1+L+R term.  The other is left as a balanced modulator being fed L-R and pilot at its modulation input.  The two signals are then summed, low pass filtered to allow the clipper to recover the carrier correctly, and then limited.  This phase modulated term is used as the carrier drive for a stereo transmitter.

Any practical implementation also involves adjustable delay and equalization networks necessary to allow the exciter to precisely duplicate the amplitude and phase response of the transmitters modulator stage.  Because real world transmitters have both group delay and amplitude roll off in the modulator, the response must be duplicated for the signals feeding the quadrature modulator or the stereo separation loop will never be closed, and poor separation will result.

It should also be noted that a precise demodulator is required to properly setup such a system, such as a modulation monitor modified to receive your transmit frequency, or with less precision, a stereo tuner with wide IF filters installed.

For the average joe, the linear amplification approach is a lot less involved and requires far less precision and hard to build/buy gear.

+-RH

777

The RF Workbench / Re: AM stereo Generator designs plus 300 watt Digital RF

« on: December 08, 2017, 2023 UTC »

There never was a am stereo modulator IC akin to the BA1404, all the generators that are out there that I have seen use discrete modulator stages, delay and equalization networks, then finally a clipper stage to recover the phase modulated carrier.

For those folks who are happy with low level modulation followed by some serious linear amplification, you can do what I did in the old transmitter.  Take the signal from a c-quam test signal generator and mix it with a tunable LO which you could get from a DDS.  Filter and amplify the output....simple.  I do have PCB artwork for the mixer and filter stage in gif if anyone is interested....schematics too.

+-RH

778

The RF Workbench / Re: Derate ceramic capacitors for DC bias

« on: December 04, 2017, 1810 UTC »

This is dependent on the type of dielectric being used.  X7R and other non-NPO types being particularly vulnerable.  Also as I found out, bypass caps can act as piezoelectric speakers.  There are some thing that can be done to avoid this.  For critical applications, RF type NPO's such as ATC parts are recommended, or better yet metal clad mica types.

+-RH

779

The RF Workbench / Re: Any DDS 200 watt AM Transmitters or kits

« on: December 04, 2017, 0255 UTC »

Of course...and MW.

One of the problems I noted when building these things is getting proper drive to the PA stage.  The PA I'm working on has the necessary circuitry built in, all you need to do is provide TTL drive from an exciter  The stereo exciter will have a means to do this from a quadrature DDS source which can be disciplined to whatever you can afford (cesium fountain clock anyone, lol).  C-QUAM will be included, Kahn may be as well if I can build precise enough phase shift networks.

Not for the faint of heart, everything will be surface mount with the exception of the power components.

+-RH

780

General Radio Discussion / Re: Pirate Radio is a Costly, Overlooked Problem—and It’s Thriving

« on: November 30, 2017, 0342 UTC »

Weller says the noise floor is a common problem that doesn’t just plague AM. It’s one reason why HD Radio FMs needed a power boost and why when VHF television stations switched from analog to digital the coverage was not as good as expected, especially indoors.

The second canary in a coal mine: the fact that even with new digital broadcasting technology they have to boost power in some way just to make a signal listenable -- and as more RFI predominates, that need for some way of boosting the digital signal will increase.

This especially applies to AM, where digital can work, except the stations need to be fully digital and probably have more power to actually be listenable in most of their metro.

Power = electricity produced from burning coal in much of the U.S.

The only conclusion I can reach (sarcasm button on) is that RFI causes more global warming (sarcasm button off).

There may be some comfort for you in the fact that modern transmitter efficiency is better than most of the older analog boxes.  Still pretty aweful by FM and AM standards, but state of the art efficiency now is around 45% AC to RF efficiency, older boxes were lucky to break 25%.

+-RH