Hi Folks,
I was wondering if anyone had any experience with the Radio Associates AMM-HF1 Modulation Monitor ( http://www.radioassociates.com). I bought one of these a few weeks ago, and am having trouble getting to work with my trusty little Rangemaster.
Hi Folks,
I was wondering if anyone had any experience with the Radio Associates AMM-HF1 Modulation Monitor ( http://www.radioassociates.com). I bought one of these a few weeks ago, and am having trouble getting to work with my trusty little Rangemaster.
They sent the AMM with a matchbox to hook it up to the output of the transmitter, assuring me that they had tested it with several part 15 rigs and it worked well. What I get when I hook it up is a distorting of the audio on the transmitter and no drive or display for the mod monitor. I emailed the manufacturer which then suggested that I put a 10k pot in line to help match it better to the transmitter. That had no effect.
Oddly, when I tap one side of the input power lead to the center pin on their matchbox I get just enough drive to light up the display, but not enough to get an accurate reading. When I do this my audio is not affected.
Steve at Radio Associates has suggested that I try one of their off-air monitor pickups (for an additional $150.00) or roll my own off air pick up. Having spent over $400 so far for this rig, I am not keen on spending another $150. This looks like a nice little rig, well built, but I am puzzled on how to get it to work.
Anyone out there have experience with this or other modulation monitors?
Thanks!
I haven't used that unit, but I have been looking at it on their web site and was thinking about getting one myself.
With only 100mW to deal with, I would assume that the off-air pickup would be required. In fact, that is the impression that I get from their web site.
Do they provide a schematic to build your own off-air pickup? If so, what does it require?
They sent me a PDF of the owners manual for the off air pickup that includes a schematic. It has around 40 components, and looks more involved than I'd care to proto-board together.
I did get a response from them a little while ago, suggesting:
"You *might* be able to use a sort-of current transformer - or capacitive coupling. If you wrap a few turns of wire around the antenna, near or at the base, you might achieve enough coupling. Try a 5 turn loop - one end of the loop to the inner conductor, the other to the shield of the cable feeding the mod monitor RF pickup, or connect to the pickup directly. I've never tried this - it may or may not work."
If the weather is decent I'll give that a go this weekend and post the result...
JGanley,
Please contact me at [email protected]
Thank You,
Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org
Moderator Hunterdonfree
http://groups.yahoo.com/group/hunterdonfree
I tried the suggestion from the manufacturer to try looping several turns of wire around the antenna for the pickup - no go. So it looks as if my options are to shell out another $150 for their powered pickup unit or roll my own.
So... the moral of the story is that the true cost of the AMM1 for RangeMaster users is just a little shy of $600, by the time you buy the AMM1, the pickup and shipping.
I do want to add - REA is prompt in responding to support emails, and the unit looks well built. But it will not work with the RangeMaster without the powered off air pickup.
-Jim-
AM1700.info
Guy does anyone have a layout of how to install the AMM HF1 modulation monitor. I just recently retired and my wife suggested that I take up a hobby. Both of the local radio station are local in FCC rules only. The only time the local town is mention is when they do their required hourly ID. ThereFORE I decided to operate a Part 15 RADIO STATION. It is not going to be a $1500 project as some selling the equipment states I need a layout so I will not have to pay the men who
are installing my equipment while they read the mannual. By the way it would not have been $1500 even if I was able to install the equipment
charles.
Well to do it right look at spending about $1500 for a transmitter and related installation components. $600.00 for the mod monitor. about $5-7k for the studio equipment. to do it cheaply about $500 for the transmitter setup. an old shop type o-scope. a DMM. and about another $500.00-$1000.00 for low end consumer studio gear.
prices will vary depending on resourcefulness.
See http://www.am1000rangemaster.com
Thank You,
Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org
Moderator Hunterdonfree
http://groups.yahoo.com/group/hunterdonfree
You can spend a little or a lot...
The results depend on how much you want to tinker, how picky you are about quality, and how much you want to spend. And a whole lot of sweat equity.
For my little station, I decided to use the Rangemaster and a mod monitor because I have limited time to tinker, and I wanted to avoid getting wacked with a fine.
But my "studio" is a 3 year old celeron PC, some audio editing software, an $80 behringer box via Ebay and a $30 microphone.
So far I have probably spent $1,600 on my part 15'er. My next big push is to actually produce some local content. But you really can do amazing production with software and a few decent microphones.
-Jim-
AM1700.info
Hi All,
It may not be well known here, but there are always a ton of good quality oscilloscopes available on eBay for a couple hundred dollars or less that will serve the purpose better than any modulation monitor. An oscilloscope will allow you to view the actual modulation waveform, so you will not be at the mercy of whatever whiz bang modulation monitor design that comes along. I'm not knocking the AMM-HF1. It may be a very good unit for all I know, but you can do better for less money.
Go to ebay.com and search on "oscilloscope". My recommendations are:
1. Don't look at any of the older scopes that use tubes.
2. Look for a name brand like Tektronics. Models 465, 475 or 485 are good choices.
3. Be sure at least one probe is included.
4. Get interested only if the seller says it works and shows a picture with a waveform displayed.
5. Don't be concerned about whether it has been calibrated recently or not. The absolute voltage reading isn't important.
These scopes are very sensitive so a wire loop connected between the probe and scope ground will serve well for a pickup. Length of the wire depends on how far your TX is from the scope position.
Take a look at http://www.sstran.com/pages/sstran_fsscopepics.html for examples of under-modulation, 100% modulation, and over-modulation. These waveforms were taken by simply clipping the probe to an insulated antenna wire (no electrical contact).
What bandwidth is really needed for an oscope if using it just for a modulation monitor? Would a person get better performance by using a ferrite antenna from a really cheap AM radio? Or would you likely get too many other signals to be of much use?
Hi !
The AMM-HF1 does indeed work very well with part 15 transmitters, and this has been done many times. However (and this is well documented on their website), you MUST use an off-air interface (which you can get from the company), or provide your own interface. The off-air interface is the easiest and most fool-proof method of connecting a part 15 transmitter to the modulation monitor.
Under certain specific circumstances, you may be able to connect the AMM-HF1 directly to a part 15 transmitter without an off-air interface. This will depend on the antenna impedance, and a number of other factors. Unless you really know what you are doing, I would recommend against it. The company will offer suggestions for those who want to try it.
However, under most normal circumstances you cannot connect any modulation monitor directly to a part 15 transmitter at the RF output. Using an off-air interface is the best method, and consumes no transmitter power.
For users who want to build their own interface, the company does provide documentation to aid in constructing an off-air interface. PC boards and parts are available from the company. Most users use the factory-built version of the interface.
From the web site, the monitor is $399 and if you need a factory-constructed off-air interface, it is $149.
-sc
What bandwidth is really needed for an oscope if using it just for a modulation monitor? Would a person get better performance by using a ferrite antenna from a really cheap AM radio? Or would you likely get too many other signals to be of much use?
The bandwidth only needs to by somewhat above the max RF frequency you are looking at (1.7 MHz).
You would have to stoop pretty darn low to find a scope on eBay with that low of a bandwidth. A couple hundred dollars will get you at least a 50MHz or 100MHz scope.
These scopes are very sensitive so a wire loop connected between the probe and scope ground will serve well for a pickup. Length of the wire depends on how far your TX is from the scope position.
This is a follow up to the above comment that I previously posted. If you want a monitoring setup for your scope that is selective to eliminate interference from other off frequency stations, you can use any AM radio as a front end to the scope. On older AM radios, you can connect the scope to the output side of the IF transformer. If you have a newer "single chip" radio, connect the scope to the ceramic IF filter. Try both sides and pick the best.
By using an AM receiver, you will get the benefit from the tuning stages to filter out unwanted stations. By connecting the scope to the IF stage, you still get the RF waveform at 455 kHz. As long as the radio isn't overloading the modulation display will be good.
You can modify your "off air monitor" radio by sodering a short wire to the IF stage and running it out to the back of the radio. You can still use the radio normally. It will just have a scope probe hanging off the back.