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RELIABLE FM TRANSMITTER FOR HOME USE




 
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Author Topic: RELIABLE FM TRANSMITTER FOR HOME USE  (Read 1182 times)
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W2PFY
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« on: January 16, 2018, 04:49:01 PM »

I want to be able to run a legal FM transmitter for my own use in my own house, I thought I would get a cheap five watt chinese FM stereo transmitter so I could turn it down to one watt.
 (Headroom)

I would be running that 1 watt into a 50 ohm resistor with about a 1 foot pigtail coming off the hot end of the resistor acting as the antenna. The antenna will be located in the cellar about 5 or 6 feet below street level so I am not too worried about getting some DX with the transmitter.

The question I have is if anyone is using a transmitter out there for this purpose, would you please let me know the model and make of your transmitter. There are a ton of them out there and I don't know what is a good pick?

If you don't want to talk about it here, PM me please.

Thanks Terry   
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N1BCG
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« Reply #1 on: January 16, 2018, 06:38:34 PM »

There's nothing illegal about owning or operating an FM transmitter of any power level as long as you take precautions against excessive radiation as outlined under Part 15. Since that's in the plan, you're all set.

As you've noticed, there are numerous FM transmitters out there ranging from true Part 15 to pro-broadcast to Chinese imports with the latter being the most common. Of those, look for the lowest power output so that it's easier to control using simple methods.

One possibility is the V6000 model from https://mobileblackbox.com

That model is relatively inexpensive, low power, but monaural, if that matters.
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WD4DMZ
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« Reply #2 on: January 16, 2018, 07:28:44 PM »

I have a Ramsey FM100B that came as a kit in 2009. 100MW but with a 1/4 vertical good stereo reception about 1/2 mile. At 100MW it meets the part 15 rule as I read it.

I used it at the HS where I taught physics and let the students broadcast with it. Dual channel plus mic input with level adjustments and LED bar displays.

Search for local stations and you will likely find an open channel. Mine is set at 90.9.

Ramsey no longer makes these but they are likely on EBAY.

Rich
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Jim, W5JO
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« Reply #3 on: January 16, 2018, 08:39:55 PM »


Ramsey no longer makes these but they are likely on EBAY.

Rich

Is this one of the things that Ramsey got into trouble with the FCC for selling?  I know they were raided and had to face some legal actions, but can't recall. 
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KD6VXI
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« Reply #4 on: January 16, 2018, 09:24:01 PM »

Ramsey made a 'whole house' fm transmitter.

Then they also made a radio station.  Complete with capabilities into the //watts// range.



https://transition.fcc.gov/eb/Orders/2006/DA-06-136A1.html

This is completely different than the raid when the feds where looking for 'spy equipment'.

--Shane
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WD4DMZ
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« Reply #5 on: January 16, 2018, 11:13:46 PM »

Ramsey sold a higher output version that was for export only. The version I have maxed out at the part 15 level. It might be only 35mw.

When Ramsey exited the business a few years ago someone bought their inventory and posted it on EBAY. I checked EBAY and found no FM100B but there were kits available to up the power of the 100B to 1 watt. Those are a no no in the US.

There was another lower featured unit from Ramsey as well but they are no longer on EBAY either.

For a while, people were building the export versions and selling them over the internet but I can not find any of them now.

I used to buy quite a few kits from Ramsey for my students to build. Many, many students learned a lot about kit and circuit construction and soldering using those kits. I was sad to see them go away.

Rich
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R. Fry SWL
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« Reply #6 on: January 17, 2018, 07:46:37 AM »

Background Info:  In areas where the FCC has jurisdiction, the maximum field intensity permitted at a distance of 3 meters in any direction from the transmit antenna of a legal, unlicensed transmit system using the 88-108 MHz band is 250 V/m (see U.S. 47CFR 15.239).

A linear, 1/2-wave, center-fed dipole in free space just meets that limit with only 11.43... nW (0.000 000 011 43... watts) of Z-matched r-f power at its input terminals.  It doesn't take much more power than that even with a very short, mismatched "whip" used as the radiator -- typically less than 1 milliwatt.

Very few "hobby" type operators have a calibrated field intensity meter able to (accurately) measure this field intensity.  Using a transmitter advertised as suitable for Part 15 FM doesn't necessarily mean that it does -- especially if it is rated for power outputs greater than 1 mW. 

The FCC has been active in finding and citing unlicensed FM operators not meeting 15.239.  So what to do?

One practical, but not guaranteed approach is to keep the useful range to a good FM receiver to a maximum distance of 200 feet or so.
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WB2EMS
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« Reply #7 on: January 17, 2018, 10:57:17 AM »

I've used a couple of the cheap Chinese ones. Seem a bit fragile. The first one failed after about a year. The replacement has been cranking along good until recently when suddenly the signal to the boom box near the kitchen doesn't seem to be full quieting any more. And the fan is annoyingly loud if you're in the shack when it's on. (of course if I'm in the shack, I don't need the transmitter running) Does cover the property pretty well with the supplied whip antenna, but probably over the official limit. But nice to be able to listen in while working out back.
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73 de Kevin, WB2EMS
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« Reply #8 on: January 17, 2018, 05:03:16 PM »

Put the thing in the basement, it will cover the whole house and have nil radiation in the horizontal direction.

Get the 5watt model. Easy to attenuate the signal out. Aka 50ohm pad network... no brainer.

They're so cheap on fleapay that you just go for one that looks about right, and see.
If it's good, buy a backup. Cheesy

                                            _-_-

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KD6VXI
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« Reply #9 on: January 17, 2018, 09:25:47 PM »

Ya know, this seems to be a good case for the dummy load antenna.

50 ohm loaf with a stinger hanging off the 'hot' end of the antenna connector.

Adjust length to get coverage needed.

Pic included of my whole house xmitter.. Adjustable from almost nothing to 40 watts.    Can be found in ebay for approx 350 bucks, designed to run //forever//.


--Shane
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* 1516290177015-1160719434.jpg (2275.7 KB, 4096x2304 - viewed 75 times.)
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N1BCG
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« Reply #10 on: January 18, 2018, 09:52:12 PM »

My goodness... a 40E. I had one of those in a CCA FM-2500 2.5 kw transmitter on 103.9...
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KD6VXI
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« Reply #11 on: January 19, 2018, 10:06:37 AM »

That 40E came in a package deal.

Harris fm1k
Harris fm20k

And everything else to run the station.

Yeah, CCA exciter for a Harris xmitter!  Lol

--Shane
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W2PFY
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« Reply #12 on: January 19, 2018, 06:32:49 PM »

I know of an exciter and transmitter that are still in use on a Bible Beater network. It looks really neat (the exiter) with a bunch of 7 & 9 pin tubes sticking out horizontally from the upright chassis. I don't remember the make or if it used a 2E26 or 6146 as the IPA. An exciter like that would probably draw more than 100 watts which wouldn't be good for a 24/7 home transmitter? 
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« Reply #13 on: January 19, 2018, 10:24:22 PM »

There's something like at in a barn in Gainesville I been trying to get. From a local tech school, 10W FM, tubes in a rack.
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