The Raytheon RM-10 Monitor Amp

I found this manual from 1946 in the drawer at the WICC transmitter site, which is a sort of time capsule due to its inaccessibility. I figured I would bring it home and scan it, then return it to the file drawer out on the island.  Step one is done:

Raytheon RM-10 Monitor Amp
Raytheon RM-10 Monitor Amp

This is a cool little monitor amp, capable of driving line-level or speaker outputs up to about 10 watts or so.  It could be used as a front or input stage for a larger audio amp.  By the way, 10 watts is a lot more than it seems, if using efficient speakers to convert that power into sound waves.  Specs show total harmonic distortion is between 0.6 to 2 percent depending on power and frequency.  Lower power output levels net less distortion.

Schematic is pretty simple, a pair of 6L6’s in push-pull for the output.   Inverse feedback into the previous stage via the output transformer.  Click on image for higher resolution.

Full manual and parts list is available here.

Now I just need to get the manual back out there.

Cost of Starting a LPFM vs Cost of Internet Streaming

I have been watching the LPFM proceedings with some interest. The FCC has not exactly promised to have a filing window by the end of 2012 but indicates that it might try to do that. In comparison to such evolutions in the past, this is moving pretty fast. Those that want an LPFM station need to start planning now.  As in previous LPFM windows, the availability is for non-profit organizations only.  This does not mean all hope is lost; NPR stations are all non-profits and most of them are very successful.

One of the biggest questions is: How much will it cost?  Like all things, it varies greatly.  If I were to put an LPFM or internet radio station on the air, there would be certain minimums, such as the use of professional audio equipment, a new antenna, and some type of redundancy.

Generally speaking, radio stations and internet stations both need some type of office/studio space.  This can range from large and opulent to a closet.  The costs for these would depend on the type and quantity of equipment installed, whether the equipment is new or used, the building, the area, etc.  Those facilities also have monthly reoccurring costs such as rent, electricity, telephone service, internet service, etc.

Since internet radio stations and traditional terrestrial over-the-air radio would use the same type of studio equipment, those costs will be similar.  Here is a breakdown of the studio equipment:

NomenclatureCost new (USD)Cost used (USD)Comments
12 Channel professional audio console$6,000.00$2,500.00Used for call-in/on air
Studio Furniture$5,500.00$1,000.00Can also be fabricated locally
Microphones, RE-20 or SM-7B$250-350$100-150Per unit, several required
Monitor Amp$250.00$100.00Can also use consumer version
Monitor speakers$500.00$200.00Can also use consumer version
CD Player$500.00$200.00Professional unit with balanced outs
Computer w/ professional sound card$1,500.00$500.00For automation and sound file storage
Computer, general use$700.00$300.00General information web browsing
Computer, Streaming w/sound card$900.00$400.00Sound card should be good quality
Studio Telephone system$1,900.00$300.00Used for call in/on air
Barix remote box$240.00 (x2)N/AUsed for IP remote broadcasts
Comrex Matrix POTS codec$3,200.00$700.00Used for telephone line remote broadcasts
Misc wiring, hardware, ect$1,000.00$800.00Connectors, mic booms, wire, etc
Total$21,780.00$7,930.00 

Some equipment is not available used such as Barix boxes.  Of course, not all of this is required for a radio station, however, most local radio stations would want the capability to do remote broadcasts, take phone callers on the air, have multiple guests in the studio, etc.

For a traditional LPFM station, the transmitting equipment would entail:

NomenclatureCost New (USD)Cost Used (USD)Comments
300 watt transmitter and exciter4,400.002,000.00Smaller transmitters with higher gain antennas can also be used
2 Bay ½ wave spaced antenna$1,900.00$700.00 
125 feet ½ inch coax$350.00N/A 
100 foot guyed tower and installation$4,000.00$3,500.00Not needed if station is on tall building or leased site
STL; IP radio w/ barix boxes$850.00 In lieu of standard 950 MHz STL
STL standard 950 MHZ$6,500.00$3,500.00 Used in lieu of IP STL
STL antennas, transmission line$2,500.00$1,500.00 
FM Processor$10,000.00$1,200.00Can also use software such as Breakaway Broadcast
Misc connectors, grounding kits, etc$1,100.00N/A 
EAS unit$1,900.00N/AFully operational CAP compliant
Processing software, Breakway broadcast$200.00N/AIn lieu of standard FM processor
Total$12-24K$8-12K 

This is a generic station, most will be somewhat different due to antenna supporting structures, transmitter powers and antenna types.  For the best possible signal, a circularly polarized antenna should be used.  A two bay, 1/2 wave spaced antenna will give the maximum signal density, while minimizing downward and upward radiation.  The upward radiation is simply wasted energy, as no one in space is listening to FM radio.  The downward radiation reduction is key if located in congested areas.

For internet radio station, the following would be required:

NomenclatureCost New IUSD)Cost Used (USD)Comments
Streaming Server2,100.001,100.00Includes professional sound card
Audio processing software200.00N/ARecommend software such as Breakaway Broadcast
Audio Processing, outboard hardware650.00400.00In lieu of software
Audio Streaming aggregator 1,200 to 2,400N/AAnnually

While LPFM’s are much more expensive than internet only stations, LPFM’s have the advantage of built in marketing, which is the on air signal.  If it is broadcasting on the air, word will get out.  On the internet, some other type of marketing will be needed to spread the word.  Also, LPFM’s should also be streaming, which would incur the same costs above.

The long and short of it is, to put a technically viable LPFM on the air is not an inexpensive proposition.  It is worth the effort, however, because the advantages of an LPFM over an internet only station are great.

Why stealing is bad

Eventually, you will get caught, odds dictate.  The local engineer for Cumulus Broadcasting in Cincinnati found this out earlier in the week.  Of course, innocent until proven guilty, so I won’t assume anything.

Broadcast engineering, especially radio engineering is a small field. Sadly, when something like this happens it makes all radio engineers look bad and there is no good reason or excuse for it.

I have seen several cases where an engineer or technical person has taken advantage of their position to pilfer from a radio station.  These vary from cashing in on dud tubes from a transmitter site to taking high-value equipment and selling it on eBay.  I recall a recent instance of backup transmitter and STL systems being sold.  I cannot imagine what these people are thinking.  A transmitter, STL system, console, or even a dud tube has a serial number and is traceable.  Anything with a serial number is likely part of a station inventory list and or will have some record of manufacture and sale.

There are instances when old equipment is getting thrown out.  In that situation, I always get permission before removing anything, even from the dumpster.

I have made several trips to the scrap yard with old transmitter chassis, wire or leftovers from transmitter installations.  In those circumstances, I always get a receipt and write the source of the scrap on the back.  This way, a record is kept and if there are any questions, I can refer to it.

Generally speaking, it is better to be overly cautious.

The Gates BC250GY transmitter

This transmitter is in service at WSBS, Great Barrington, MA as a standby. It was new in January 1975.

Gates BC250GY transmitter, WSBS Great Barrington, MA
Gates BC250GY transmitter, WSBS Great Barrington, MA

This was running into the dummy load for testing, which we try to do periodically.

Gates BC250GY AM transmitter audio section
Gates BC250GY AM transmitter audio section

The audio section is a pair of 8008’s 810s running in parallel. This goes through a modulation transformer to the RF section.

Gates BC250GY RF section
Gates BC250GY RF section

The RF section consists of another pair of 8008’s 810’s running parallel. The plate voltage for these tubes is 1,250 VDC which is fairly tame, all things considered. The transmitter is dirt simple 250-watt carrier power, 125% positive peak capable.  It is not the most efficient unit under the sun but it can still be repaired with off-the-shelf parts.

Gates BC250GY Schematic
Gates BC250GY Schematic

This is a somewhat faded schematic.  The schematic shows a single 833A as the final, however, this particular transmitter has a pair of 810’s for the final, as shown in the above picture.  Ham radio operators love these things as they are easy to convert to 160 or 80 meters for AM phone use. The bigger brother to this unit is the Gates BC1G, which is also a pretty simple unit using 833A tubes in parallel with 3,500 VDC plate voltage.