[AMRadio] Broadcast Processors

Tue Jun 14 16:31:38 EDT 2011

The MBL 100 had compensation to handle a less than perfect low end. The 
first transmitters where it was ever used were 500 KW  PDM units, 250 
kilowatt plate mod shortwave transmitters and a 625 KW PDM MW TX. The  
PDM units had a design issue where the power supply choke was resonant 
somewhere in the 30 hertz range and if you hit the resonance there were 
fireworks so low end protection was necessary. Ultimately that problem 
was solved by removing the choke  and re-working the PS filtering since 
the PS was 12 pulse and the choke was not really necessary.  The plate 
mod shortwave TX was what it was. There were a lot of high power 
transmitters in the field that could not meet the ideal near DC low end 
response as the organizations that typically used high power TXs tended 
to accumulate transmitters. It is not uncommon to find a new transmitter 
in the same building as 40 or 50 year old units that are still operational.

On 6/14/11 12:13 AM, Nigel Holmes wrote:
> Radio Australia's Harris SW-100A transmitters at Shepparton used MBL-100 processors from 1993-2010. They were replaced with Orban 9300 processors. About a dozen MBL-100 went into the Australian surplus market. Haven't heard of any turning on the amateur bands.
>
> They are excellent processors, but not for the likes of a BC-610 or 300G. They like to be mounted in the transmitters (leads<  6'). The transmitter "Frequency response must be less than 3dB down at 0.15Hz, and less than 0.1dB down at 9.5 kHz." !! Then the antenna needs to be flat as well.
>
> If you find a CRL or Orban processor then use it as an excuse to build a dc-coupled PWM tx and a 160m antenna that is flat +/- 20 kHz about the operating frequency. The results will be stunning.
>
> 73 Nigel VK3DZ
>
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-bounces at mailman.qth.net] On Behalf Of W2XJ
> Sent: Tuesday, 14 June 2011 6:02 AM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Source Broadcast Xmtrs
>
> The MBL-1 was targeted to shortwave broadcasting. I put the beta on a modified Marconi 250 Kw transmitter owned by the BBC. It had some very aggressive tilt and overshoot compensation capability. It could be made to be very loud. It also had an adjustment to keep low frequencies out of the clipper. The one important feature was that it moved any audio frequency shaping to the limiter's input. The transmitter would ideally be flat from below 1 hertz to at least 3 times the upper input frequency.
>
> Two other hot boxes are the Orban shortwave Optimod (there has to be a ton of those surplus)and the hard to find Gregg Labs processor.
>
> On 6/13/11 3:48 PM, Dennis Gilliam wrote:
>> Indeed, and CRL was made just down the street from the station I
>> retired from.  They made a great limiter for AM, and never forget the
>> DAP-310 from KO6NM, either.
>>
>> 73DG
>>
>> On Mon, Jun 13, 2011 at 12:39 PM, W2XJ<w2xj at nyc.rr.com>   wrote:
>>
>>> Good low frequency response is important if broadcast style
>>> processing is used. The major name processors from the 80s and on
>>> used LF compensation to adjust tilt on clipped peaks and increased to
>>> amount of usable modulation. Those equalizers were designed to match
>>> the typical plate mod transmitters around at the time which went down
>>> to somewhere between 30 and 50 hertz. A 300 hertz cut off is far from
>>> adequate when a good processor is used before the transmitters.  If
>>> you want a screaming processor, try to find a CRL MBL-1.
>>>
>>> On 6/13/11 2:47 PM, Dennis Gilliam wrote:
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