Very low power recommendation

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NECRAT
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Very low power recommendation

Post by NECRAT »

Hello brain trust...

I need advice that the Google-matic machine is not helping.

I am taking on a very small class D fm that is a mess, but in the process of being cleaned up.
The FM is a whopping 6 watts TPO. Currently the station has a Superior Broadcast Products 200 watt transmitter, with the needle just barely making the first mark, (in other words, around 6 watts). This is not ideal. Aside from using a 200 watt transmitter for 6 watts, the transmitter itself is quite old. I honestly have never heard of Superior Broadcast Products before, and I am thinking they bought this transmitter at Sears. At least if it had a "Realistic" logo, then I'd know where it came from. All joking aside....

So I've been searching online for a smaller transmitter, similar to a BE FX-50, and Google keeps suggesting CZEH-50 ebay transmitters(!). Great for the neighborhood pirate, but terrible for this installation.

Any recommendations for something to give this low power? Would the FX-50 be a good fit?
Mike Fitzpatrick
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TPT
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Re: Very low power recommendation

Post by TPT »

Both the FX-50 and the similar Continental products (802 A and B) while good exciters,, are not really happy running at very low power. They use Darlingtons for power control--essentially like a variable power divider. At 40~50 watts they are quite happy, at 10 watts they are dissipating a lot of power as heat.

I would recommend an Armstrong or Bext exciter, they run around 30 watts. RVR is another choice--many of the Armstrong/Bext models of the past were actually made by RVR.

In any event, no matter what you use, plan on adding an external second harmonic filter. Microwave Filter makes them, there are other companies I'm sure.

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Re: Very low power recommendation

Post by NECRAT »

TPT wrote:
Sun Mar 03, 2019 6:20 pm

In any event, no matter what you use, plan on adding an external second harmonic filter. Microwave Filter makes them, there are other companies I'm sure.
That was already in the plan. :) Along with about a half dozen other things...

I never heard much good about the Bext Stuff, would that be a good route to go?
Mike Fitzpatrick
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Re: Very low power recommendation

Post by TPT »

Had an older Bext on a translator, generally trouble free, but would get finicky if the frequency changed (thumbwheel on front--didn't necessarily land where you thought it would). A lot of the Bext products are RVR's, same with Armstrong. Have an Armstrong 30 watt I use on a backup transmitter, works fine. My inclination--budget permitting--would be to go with the Armstrong FMX-30.

Output filters: Look at the ones on this page--https://broadcastconcepts.com/82/ Prices look good.

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Bill DeFelice
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Re: Very low power recommendation

Post by Bill DeFelice »

I don't know if any of the lower power Broadcast Warehouse products are type accepted / certified for LPFM operation but I used one of their TX5 FM transmitters for a radiating coax in-building FM signal for a high school radio station project a number of years ago and it kept chugging happily without any problems other than the display getting dim.
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Re: Very low power recommendation

Post by TPT »

That's another issue. If this is a true "Class D" then anything with an FCC registration number is acceptable. Station, of course, still responsible for out of band emissions. I have a Class D at the local college I take care of--uses an MX-15 followed by a "scuba tank" sized band pass filter. We had a mixing problem with an LPFM on the same tower--mixing product came out on 100.9 which was the frequency used for a Class A 20 miles away. That station came on the air in 1950 with a Gates 10 watt tube transmitter (exciter with built in harmonic filter), it's presently running 4 watts ERP.

LPFM's are supposed to use transmitters accepted for LPFM use, most of these run a minimum of 150 watts. Of course, they have a height restriction--there's one up in NW Ohio on a former AT & T tower running at 27 watts, some 200' ag.

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Re: Very low power recommendation

Post by Deep Thought »

You might want to check out the Nicom NT-30. It already has the low pass filtering and also has an internal stereo generator.

As noted, for an old-school class-D you can use anything type accepted for Part 73 operation.
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Re: Very low power recommendation

Post by kcbooboo »

You can also tell google NOT to return results from specific sites (such as ebay) by adding a hyphen and the major part of the site name (no space between them), as in:

10w fm transmitter -ebay

It's unfortunate that google returns ebay auctions for stuff that's long-gone, sold, or even non-existant any more.

You can use the same trick on ebay. I do that often when looking for a particular piece of test equipment, rather than its manuals, by using:

agilent e4430b -manual -manuals, -guide -guides

Note that ebay doesn't allow wildcards any more, so you need to include singular and plural keywords.

Mark Persons used Broadcast Concepts pallet amps and low-pass filters in a lot of exciter repairs. He'd also install a 1/4 wave stub for some arc protection when the unit was driving a tube final, but that's good protection even if the unit is feeding an antenna directly.

Bob M.

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Re: Very low power recommendation

Post by NECRAT »

kcbooboo wrote:
Mon Mar 04, 2019 4:15 am
You can also tell google NOT to return results from specific sites (such as ebay) by adding a hyphen and the major part of the site name (no space between them), as in:
Bob, Google changed something in the last year and the "-" trick doesn't always work. It works only sometimes. I think they use an algorithm to get things to pass around it. Believe me, I tried it.

Mark, thanks on that suggestion. That may be the route I go.
Mike Fitzpatrick
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Re: Very low power recommendation

Post by KPJL FM »

10w fm transmitter -ebay
seems to work on DuckDuckGo.
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Re: Very low power recommendation

Post by Dale H. Cook »

NECRAT wrote:
Sun Mar 03, 2019 5:50 pm
So I've been searching online for a smaller transmitter, similar to a BE FX-50 ...
What about a BE FX-30? That should be happier at 6W than an FX-50 would be.
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kkiddkkidd
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Re: Very low power recommendation

Post by kkiddkkidd »

The Broadcast Warehouse tx's are pretty good and reasonably priced. They have a 30w single RU unit that should go down to 6w. I have seen a number of 10w exciters over the years but don't recall a single modern 10w unit.

SOME other high power exciters won't go down below about 5 or 6 watts. I installed a BW 150 as an exciter / backup TX to an HT5 and it just barely will go low enough to not trip the overdrive fault on the TX. IIRC, about 8w was the absolute minimum that it would make.

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Nathaniel Steele
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Re: Very low power recommendation

Post by Nathaniel Steele »

Crown classic 30watt. not sure if they still make them. the new crowns are Ecresso's and theyr'e ok but I like the classics better. BW stuff is ok and has gotten better over time. BE FXi60 is one of my favorite exciters, had one driving less than 10 watts an RVR PA. worked fine sounded great. still does AFAIK.

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Re: Very low power recommendation

Post by Ray »

There was a BW TX-5 V2 5 watt transmitter on ebay last week. I've used a BW TX-50 as a standby. It has a simple 4 band processor included,
The only problem is the display seems to go bad with time. Has a good remote interface.

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Re: Very low power recommendation

Post by jthorusen »

Get yourself a couple of hundred feet of RG-58. Coil it up (loosely so it doesn't get too warm) in the back of the rack and connect to the transmitter and thence to the RF distribution or antenna feed line or whatever. Roughly 10 dB at 100 MHz. Should knock down harmonics even more. Cheaper than a new transmitter.

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James K. (Jim) Thorusen
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