Dave Richards AA7EE

October 30, 2010

New Kit Company To Debut Trail-Friendly Radio

Most people reading this post will be familiar with Jason NT7S, or at least have heard of him.  He’s an amateur who lives in Beaverton, Oregon with his wife Jennifer, their golden labrador Baxter and newest addition to the family, their 3 month-old son Noah.  Jason recently did something that I consider very admirable – he gave up full-time employment in order to be able to spend more time at home with his family.  Jason is planning to launch a new open-source amateur radio kit company and as part of that has been working on “Project X”, which it has just been revealed is a CW transceiver with a superhet receiver. The current draw will be 30mA or maybe even a little less, a fact that will make it very appealing to hiking and camping folk. Much use is made of cascode JFET circuitry.  The radio includes a built-in keyer, frequency counter and battery check status indicator too. It has a 4 pole crystal filter with an approximate bandwidth of 500Hz (nice) and will be available intially for 40M with plans for other bands as well.

I could tell you a little more, but I’ll send you over to Jason’s site for the lowdown.  Two things to bear in mind before you go look:

1) The picture is not what your finished radio will look like.  This is his prototype that you’re looking at.  The final kit will be smaller, make use of SMT’s and will have a PCB.

2) These are early days.  It’s not going to be available next week, so now might well be a good time for you to give Jason feedback on something you might want in a kit like this (hope Jason doesn’t mind me saying this.)

For my part, there are two things that are quite important requirements that not all single band kits provide. Here are my two desires –

1) A smooth and fairly slow tuning rate and

2) a really nice sounding sidetone (rough square wave type side-tones really kill my enjoyment of sending CW)

That’s it.  Boring I know, but those 2 features make a big difference to my enjoyment of a radio. What would you like to see in a trail-friendly TX/RX? (Jason’s going to KILL me for asking this!)

Oh, and the very best of luck with the new business Jason.  We might be in a recession, but the best ideas will always do well – even in a tough business environment like this. When you get things off to a good start, think of how they can grow even more when the economy improves. So everyone please wish NT7S the very best in his new endeavours and if you’re going to be in the market for a cool new CW transceiver kit in the near future, you know where to look!

Here’s the link to Jason’s post.

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October 28, 2010

QRP Labs QRSS TX Kit

What’s not to like about a transmitter kit that costs 10 pounds sterling and can get you spotted all over the world under the right band conditions?

For your ten quid, you get this QRSS Transmitter Kit from QRPLabs, designed and manufactured by Hans Summers G0UPL and Stephen Farthing G0XAR:

I think he transposed the last two letters of my callsign......

After reading G4ILO’s account of receiving his kit and how his keyer chip was sent programmed with the callsign G4LIO instead of G4ILO, I was hoping that my chip wouldn’t have any of my call-sign letters transposed also. I breathed a sigh of relief when I saw the paper in which the chip was wrapped with the marking “AA7EE”. Then it dawned on me that my situation was potentially much worse than Julian’s.  Either the last or the first two letters of my callsign could have been transposed by Stephen and I would never know. This uncertainty has the potential to keep me up at nights, but I’m made of pretty strong stuff.

OK, stuff a few parts into holes, wind a few toroids, put it into a food container (one of a package of 4 that I got cheap from Ross Dress For Less) and here we go:

PL259's aren't my ideal RF connector for small projects like this but my local HRO don't carry BNC's anymore. Good grief, what is the world coming to? A Ham Radio store that doesn't carry BNC's? Somebody give me a whiff of salts please.

The board is a good quality single sided board.  I find this kind of board just a little (not much) harder to solder to than a double sided board with plated-through holes, the reason being that if you’re used to the the latter, it can be quite easy to put too much solder on your joints (there are fewer places for solder to go). So go easy with the solder folks. Be careful and you’ll be fine.

On firing up the transmitter, I noticed that although I had connected pin 7 of the keyer chip to the +ve supply line, the chip was sending CW at slower than the 6 second dots I was expecting – it looked like 15 or 20 second dots.  A look at the QRPLabs Yahoo Group and I realized that a few others had experienced this problem too.  Pins 5,6 and 7 are used to tell the chip what speed to send your callsign at.  The cure is to ground any unused pins.  If you will be changing the speed regularly, then you can install 10K pull-down resistors on pins 5,6 and 7.  Either approach works. Thank you QRPLabs Yahoo Group!

The signal is surprisingly stable after initial warm-up.  I did find it to drift a little on occasion, though I think these drifts of up to 10Hz were caused by changes in room temperature.  Most of the time, the TX stayed to within a couple of Hz of where I set it. If the temperature of your radio room is thermostatically controlled and room temperature doesn’t vary much, you should be fine.  For anyone thinking of mounting the transmitter outside or in some other non temperature-controlled environment you may need to think about insulating the box, or using some kind of crystal oven.  A bigger problem for me right now is that the trim cap that sets the exact crystal frequency is very sensitive.  It’s important to set your QRSS TX on an unused frequency, so precise frequency-setting to within a few cycles can be important.  It makes no sense to put your signal on top of a strong signal.  In a band segment that is only 100Hz wide it’s worth finding as clear a part of it as possible. The 25pF trim cap and an inductor are in series with the crystal to pull the frequency.  I’m thinking that removing a few turns from the inductor might make the trim cap cover a narrower frequency range, making it easier to set the frequency of operation of the transmitter.

The first night of operation didn’t yield any reports, and I didn’t see myself on any online grabbers, but I don’t know how much power I’m putting out.  I don’t have a QRP power meter and for some reason I can’t get any reading at all from my my home made RF probe.  I wasn’t expecting it to be accurate at these low power levels, but I was expecting some kind of reading.

But this is kind of a moot point anyway.  I don’t know why this didn’t occur to me before, but Spectrum Lab has the capability to send QRSS as well as receive it, so if I get myself a decent QRP power meter (which I have been wanting anyway), I can use my FT-817 with Spectrum Lab to transmit QRSS and can dial down the audio drive to the rig to achieve any power level I want. An added advantage of using software like Spectrum Lab to transmit is that I can make some fancy patterns on the bands by sending Hell.

There are not a lot of good QRP power meters out there.  Various QRP groups (including NorCal) have in the past offered kits but I don’t know of anyone who is offering one now, with the exception of the time-honored Oak Hills Research WM-2 QRP Wattmeter.  For QRP, I like gear that is small, but this watt meter has analog meters, which make the process of adjusting a circuit for maximum power more pleasant than watching a digital readout. Analog meters still have the edge in ease of use when you’re adjusting anything for a peak.

So do you guys know of any other readily available QRP Wattmeters? Does anyone here own an OHR WM-2 and if so, what do you think of it?

Back to QRSS before I end this post. I did have a fun evening and overnight on 30M spotting various stations.  My first few hours listening (watching?) netted me KC7VHS, KE5OFK (who I hope to chat with on 2 meters when he visits the Bay Area in a week or two), W4HBK, W0TJ, and WA5DJJ (who was runing 10mW 955 miles away from me in New Mexico!) I sent e-mails with screen grabs attached to all stations heard and had really nice replies from all but one.

I was excited to see David WA5DJJ’s 10 milliwatt signal. When reading the CW, remember that it is the signal directly above the red lettering, and that you are looking at the top parts of the waveform, not the bottom parts.  It’s a little weak, but perfectly readable, and it is just 10 milliwatts – that’s 0.01 watts – way less power than a flashlight:

David (in Las Cruces, New Mexico) has lowered his signal to 125µW and has already been copied by W4HBK in Gulf Breeze, Florida. Astounding stuff! David has even lowered his output power to 65µW!  I’m not sure if anyone has copied him at that level yet.

Next is Bill W4HBK.  Bill worked for NASA on the Gemini, Mercury, Apollo and Space Shuttle projects and it seemed very appropriate to be sending a weak signal report to a guy who worked an agency who knew a thing or two about even weaker signals. Bill has a particularly good grabber online at http://www.ohr.com/wattmeter.htm As well as a regular 10 minute scan, he has a 4 hour scan.  If you know the exact frequency of your signal you can look for it on the 4 hour scan to identify a time when propagation was best, then go to the archive of the 10 minute scans to verify that he was receiving your signal.  Brilliant  – services like this are very helpful to experimenters. This is what Bill’s 250mW signal to a 43 foot vertical with a good ground in Florida looks like in California – 2062 miles away. Just above Bill is Larry WB3ANQ’s 200mW “snake” into a Force 12 40XK vertical dipole:

To anyone who thinks that amateur radio is just a bunch of old guys chatting to each other and has lost it’s experimental nature, what is going on in the general area of weak signals is a perfect example that the pioneering spirit is alive and well. Joe Taylor K1JT has worked wonders with WSJT and WSPR.  JT65 has made it conceivable that with a fairly modest station, I could get to work moonbounce one day.  There is a hardcore of experimenters in the QRSS community who put a great deal of effort into building very stable transmitters in order to have their weak signals copied down to lower and lower levels. It’s fun to see this all activity going on.

The next projects at AA7EE will most likely be procuring (or building) a QRP wattmeter, and designing some coaxial traps to turn my 30M inverted vee dipole into a trap dipoole for 40, 30 and 20.

But right now, I just ate dinner and need a nap.

October 23, 2010

QRSS on 30M and My New Dipole

I’m not sure at what point QRSS came into sharp focus for me, but it represents quite a logical step given my interest in QRP.  A couple of years ago, I remember finding out about illegal unlicensed low power HF beacons (as opposed to the legal unlicensed Hifer beacons) and even hearing a few. I seem to remember that there was one somewhere around 4096 KHz located out in the Southern California desert (probably solar-powered) that I could hear in San Francisco. Hearing the weak dashes on my radio that were coming from a small transmitter out in the desert somewhere really held my attention.  I wanted to put one on the air myself but a) they were illegal and I hold an amateur license and b) as much as I liked the idea of hiking out to a remote area, hiding a transmitter and then being able to listen to it at home and from other locations, leaving an unmanned transmitter, even a QRP one, transmitting for long periods of time didn’t seem very responsible – especially as I didn’t know who else was using that segment of the spectrum. At that time I didn’t know about the so-called unlicensed Hifer beacons operating in the 13553 – 13567 KHz band or I might have put one of those on the air.

Amateur Radio to the rescue.  We really are lucky to have so many RF spectrum privileges. If necessary, we can use up to 1500 watts of power on many bands, and we have no antenna limits. So if you have the resources and the time, you could squirt 1.5KW of power into a 5 element beam on 80M. Sometimes, that kind of power is necessary to get the job done.  Try asking the SSB EME folk if they’re happy to be able to use high power into any antenna they like. Some (for which read many) things you can’t do under Part 15 regulations, and EME is one of them :-).

I digress. I think the big trigger for me was seeing a post on AE5X’s blog in which he talked about a QRSS transmitter kit designed and manufactured by Hans Summers G0UPL and Stephen Farthing G0XAR. He posted later to report his successes with this transmitter. G4ILO has also been busy with the same kit, also with good success (well, after he received his chip programmed with two of the letters in his call-sign transposed. I don’t know Julian personally but from my perspective as a reader of his blog, it seems that he wouldn’t be Julian if something didn’t go wrong every now and again.)

The 30M QRSS Transmitter kit ordered I sat back and figured that while waiting for the kit to arrive from the UK, it might be useful if I had an antenna for 30M. Since moving to my current place, I’ve had a length of wire taped to my 32 foot fiberglass mast tuned against a “ground” consisting of a cold water pipe which I have recently discovered might not be connected to ground very well, if at all. It works appallingly. For all my adult life, I have always used either good antennas in compromised locations,  or just plain awful antennas, not to mention the excruciatingly ghastly antennas deployed in equally frightful spots.  It was time for salvation in the form of a simple yet effective antenna erected high and in the clear, and luckily my current QTH offers some hope in that regard.

Allow me to set the scene.  Imagine two trees at either edge of the property I live in, spaced about 70 feet apart.  Each tree is about 40 feet high, with my second floor balcony and it’s 32 foot fiberglass mast (with the tip standing at 47 feet above ground) roughly in the middle.  Now picture this:

One look at this and your childhood will flash before your eyes.

It’s the EZ-Hang and it’s an adult excuse for picking up a slingshot again. I had wanted to use 1 oz lead fishing sinkers for the weight but I live in a built-up urban area and there are too many car-roofs, windows, and people around to risk it.  The mini tennis ball came in a pack of 4 from a pet shop and will shoot high enough for a 40 foot tree. Added to that, it is brightly colored and easy to spot once it has fallen back down to the ground. Many other ways exist to get a line up into a tree. You can use a regular slingshot and fishing line on a separate spool, some people use a bow and arrow,  or you can fill a small pouch with sand or stones and toss it up into the tree.  Your call, but whichever way you do it, it’s fun being outside and stringing antennas up. The easy way to do this is to shoot your projectile over the tree and not through it.

I use very lightweight 4lb test monofilament in the reel. Once the tennis ball has fallen the other side of the tree, I cut the ball off, tie heavier monofilament to it (40lb test) and reel that back through the tree. The 40lb test monofilament ties directly to the antenna wire – no insulators needed. It’s also hard for neighbors to see and dislike. Heck, if you use thin stranded antenna wire with a light or white insulated coating, it’ll be tough to spot from the ground when viewing it against the sky.

Here’s the dipole center insulator, made from the lid of a peanut butter jar:

I could have soldered the coax directly to the dipole elements, but had just bought a new length of mini RG-8X with PL259's fitted on each end and wanted to preserve them.

The back of the center insulator with dipole elements soldered on:

Shame there's no more peanut butter.........

The center insulator needs waterproofing.  I just discovered a product called Brush-On Electrical Tape (or Liquid Tape – same stuff), which is like having a roll of electrical tape in liquid form that you just brush on:

The back of the SO239 with two coats of Brush-On Electrical Tape. After this photo was taken, I added one more coat to make sure (it was beginning to rain as I did this.)

….and some of this really fun goop on the PL259 too:

At the top of the peanut butter lid (I mean dipole center insulator) is the string that attaches to the eyelet on the top of the fiberglass mast.

Pulling the heavier 40lb test line back through the tree. If you look really closely, just above the balcony railing you can see the knot joining the lighter line and the heavier line.

A view of the mast from near the bottom, showing the mini RG-8X attached to the mast with velcro straps, and the center insulator at the top.

A quick word about pruning the lengths of the elements. You can if you want, use either an SWR meter or some kind of antenna analyzer and keep trimming the wire (equal amounts on each side) until it is resonant at the center frequency you want. A quicker way to do it in fewer steps is the following way:

Use the standard formula of 468 divided by the center frequency to give you the length in feet of the entire dipole.  For a center frequency of  10.125, the result is 46.22 feet = 23.11 feet for each leg of the dipole.  Add a little bit (say 24 feet per leg for the sake of this example,  though this would be a fine length to start out with), put the dipole up and measure it’s resonant frequency. Now do this quick calculation:

{Dipole Length in Feet} (in this case 48 )  x  {Measured Resonant Frequency in MHz} = New Constant

Now plug the New Constant into the formula:

{New Constant}  ÷  {Desired Resonant Frequency in MHz} = Dipole Length

In my case I cut the dipole to 48 feet (2 lengths of 24) and measured the resonant frequency on my MFJ-259B antenna analyzer as 9.86 MHz, so my calculation was:

48 x 9.86 = 473.28

I wanted the center frequency of the dipole to be 10.125, the exact middle of the band.  It’s a narrow band so there would be no problem covering all of it at low SWR.

So 473.28 ÷ 10.125 = 46.744

– meaning the each dipole leg should be 23.37 feet, or about 23 feet 4.5 inches.

I didn’t cut the wires – just folded them over to make the new length, elevated the center of the dipole back up to it’s full height and measured the resonant frequency again. It wasn’t perfect at 10.17MHz, but close enough. The dipole showed an SWR of 1.3:1 or below across the whole band, which is good enough.  At 10.1405, the center of the QRSS segment, the SWR is 1.1:1, which makes me very happy. Using this method makes pruning antenna lengths faster, and cuts the trial and error.

You may have noticed that I haven’t used a balun. The reason is the extra weight it would add to the top of the fiberglass mast, which is pretty thin and whippy at the top.  If you’re using a more sturdy type of support, by all means use a balun. It will reduce any RF currents flowing on the outer shield of the coax, which can only be a good thing.

So how does it work? Well, with previous antenna installations at this and my previous QTH just down the road, I had noticed that other amateurs in my general area seemed to be getting many more WSPR spots than me, and when they did hear stations that I heard, they were receiving much better signals from them. This was not just happening with the odd station here and there; it was a very noticeable overall trend. On plugging the new dipole into the back of the FT-817 (which is an inverted vee dipole with the center at 47 feet and the ends at about 35 feet) immediately 30 meters sounded more alive than I had heard it before. A few hours on WSPR and I was getting a lot more spots than before – about the same number as other amateurs in the area and with similar signal reports. With my first 2 minute TX period, I was spotted by 13 separate stations.  This had not happened to me before!

It’s one thing to know how important it is to have an antenna elevated and in the clear, but another thing to actually experience it. At 47 feet, the center of my 30M dipole is about half a wavelength above ground- a good thing. You should strive for at least a quarter wavelength in order to get something approaching the correct radiation pattern for your antenna.

Don’t worry if you can’t mount the entire dipole horizontally.  The point of maximum current is at the center of the dipole, so this is where the most radiation occurs from.  For this reason, getting the center of the dipole up high is more important than getting the ends high.

The QRSS transmitter kit should be arriving any day now, but in the meantime there is plenty of listening for QRSS stations to be done. That will be the subject of another post………

 

 

October 8, 2010

The SSTRAN AMT3000 – A Part 15 AM Transmitter

In the last post you saw my first steps towards putting a low power unlicensed (yet legal) AM broadcast station on the air from my house in Oakland, California.  I spent several months putting the programming together using a piece of free radio automation software called Zara Radio. Adding songs is not quite as easy a process as ripping songs into your iTunes.  As well as ripping the songs from CD, I have to trim any excess silence from the beginning of the song and then mark the exact segue point, so that the software knows at which point to start the next song.  It takes a little while to do this, and I have now done it for 1650 individual songs, as well as producing sweepers, promos and other little doo-das that all go to make a radio station sound like, well, a radio station. The software also automatically plays a newscast (grabbed from an internet feed) at the top of each hour after playing a news intro. It all sounds pretty nifty and I’m quite happy with the way it has worked out. So with the programming worked out, the next step was to build and install a transmitter. I had originally decided to use the Hamilton Rangemaster, but that was going to set me back the best part of a grand for the transmitter and cabling alone, not to mention the cost of outboard audio processing.  The AMT-3000 Part 15 AM transmitter is made by SSTRAN, has onboard limiting and compression and comes as a kit for around $100.  On checking reviews and write-ups, it seemed to be a high quality kit with a stable well-modulated signal and decent onbaord audio processing. The relatively high cost of the Rangemaster had dissuaded me from continuing with my low power broadcasting aspirations,  but the thought of getting on the air for $100 meant that the financial barrier to going through with this had just been removed. $200 is a little closer to the mark actually, as I would also have to fabricate a vertical antenna with loading coil and buy the cable to connect the outdoor transmitter to the studio, but this was within the realm of justifiability for me.

So this is what the SSTRAN AMT-3000 looked like when it arrived at my house. Exciting eh?

 

This kit arrives in a box. Who would have thought it?

 

On opening the box the first thing you see after the packing slip, is a clear and detailed instruction manual sitting on top of a well-packed kit. First impressions are very good.  At this point I definitely want a second date:

 

The instruction manual is detailed and clear.

 

When you open up the box, you see all the parts, including a wall-wart transformer, all knobs and connectors,  a high quality silk screened PC board and a plastic case with printed front and rear panels. You even get antenna and ground wires that are sufficient if you’re just intending to broadcast to the radios in your house (50-200 foot range):

 

This is what you get inside the box.

 

If you look closely at the above picture, you’ll see that instead of a front and rear panel, I have 2 rear panels.  An e-mail to SSTRAN solved the problem and a front panel arrived in my mailbox a few days later. It didn’t delay my building the kit as I could still complete the board, place it in the case if needed, and use the transmitter.

Although a pretty straightforward kit, this is not a project for the absolute beginner. The parts density is fairly low, but some of the individual parts have leads that are quite close together. If you have some experience soldering parts onto circuit boards you should be OK with this kit though. There is one SMT device which came pre-soldered to the board in the version that I bought.  There is also a version of the kit for $3 less that doesn’t have the SMT chip pre-soldered, but this wasn’t available at the time of ordering so I took a deep breath and decided to pony up the extra $3 (I’m a cheapskate and happen to like soldering SMT devices).

Another thing about this kit is that there are no coils or toroids to wind. I joked in the forums over at Hobby Broadcaster that I almost felt as if I hadn’t really built a transmitter because I hadn’t wound any inductors! The kit uses pre-wound inductors, which does make the whole assembly process faster and more straight forward. This is what the board looks like when fully assembled:

 

The finished board. At this point, you can plug it in and transmit!

 

Looking at the board above, at the back from left to right are the 2 audio input jacks.  It is a mono transmitter, but if you have a stereo feed you can plug both channels in here and they will be summed to a mono signal.  If you have a mono feed, it can be plugged into either connector. Hiding behind the 15V regulator heatsink is the power connector.  The kit comes with a wall-wart that outputs 16V AC, but you can also run this from a DC input; I used 24V DC from 2 gel cells and it worked fine. Finally at the far right is the antenna and ground connector. You can see the 3 RF chokes that can be placed in or out of circuit with jumpers in order to combat hum due to stray RF. 2 of the chokes serve to isolate the power input and one isolates the audio input ground from the board ground.  Because these are RF chokes, they allow audio to pass, so if you have an audio ground loop you will still need to fit an audio isolation transformer. In front of the regulator heatsink is the blue 8 position DIP switch that is used to set the transmit frequency. The transmit frequency is derived from a PLL synthesizer which gets it’s reference frequency from a 4MHz crystal (for the US version with 10KHz channel spacing), making this transmitter stable enough for most Part 15 purposes. The 4 position DIP switch to the right controls the switching in and out of circuit of several inductors for use when tuning the supplied indoor antenna. When using a base loaded outdoor vertical, the on-board inductors are not used.

The whole thing looks pretty nifty when you put it in the case:

 

Your own mini AM broadcasting station (substitute the phrase “medium wave” for AM if you’re in the UK.)

 

On the front from left to right is the audio gain control, the pot that sets the modulation level (it sets the point beyond which limiting occurs), and the compression level control.

Oh, here’s the bottom of the board too, just to prove that I can solder:

 

Look Ma, I can solder!

 

Many folk buy these in order to broadcast programming to their vintage radios. I don’t know what the AM band sounds like in other countries (or medium wave band as it is more correctly referred to in the UK), but in the US it is mainly conservative talk radio produced with ratings (and not quality of content) in mind.  The conservative part doesn’t concern me, but the fact that much of it is highly opinionated banter designed solely to push the emotional buttons of listeners does bother me no end. John N8ZYA refers to it in his blog as drivel and to my mind he’s right on the mark.

Anyway, if you just want to broadcast around your house, you’re pretty much done at this point.  You can connect the supplied pieces of ground and antenna wire, tune them up per the instructions, and you’re ready to blanket your homestead with good sounding AM broadcasts. If, like me, you’re hoping to cover a slightly larger area, then the next step is to build an outdoor vertical antenna with a loading coil.

The instructions for a base loaded vertical made from readily obtainable parts are on the SSTRAN website, and there is a drawing and parts list also. All the info is contained on the site, so I’m not going to repeat it here, but this is the loading coil made from 16 AWG magnet wire wound on a former of 3″ white schedule 40 PVC:

 

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PVC has a tendency to absorb moisture over time, so the pipe was painted with 2 coats of varnish, the coil wound, and the finished coil coated with varnish.  The ends of the pipe were masked with tape so that the end caps could be cemented into place afterwards.

Here’s the finished antenna and transmitter installation.  The transmitter was housed in a Rubber-maid container.  If I decide to make this installation more permanent, I’ll search around for a white plastic box with weatherproofing seals. You can’t see the top of the antenna, but it’s just a length of copper plumbing pipe with a cap soldered on the end:

 

Schedule 40 pipe and Rubber-maid containers – the giveaway signs that this is not a high-tech installation on the roof of some government building, but just another radio experiment at my house.

 

Here’s a closer view of my Home Depot/Orchard Supply Hardware/Safeway special:

 

At this early stage, the antenna wire is still connected to the coil tap with an alligator clip; tuning has not yet been finalized. Audio and power cables enter the box through small drilled holes and will be sealed with silicone caulk.

 

Some gratuitous beefcake; the loading coil gets it’s close-up:

 

If this Part 15 thing doesn’t work out, perhaps I could use it on Top Band……

 

So how does it work? Weeeelll……some people get great coverage and results right off the bat.  I am not one of those people, and I think I’m going to have to put quite a bit of effort into perfecting this system if I want it to work to my satisfaction. The transmitter itself seems to be doing everything it should.  The carrier is stable. The audio processing sounds good.  Considering all the processing is taken care of by one chip I’m quite happy with the way it sounds.

I’m experiencing two problems. One is that there is an AC hum on the carrier that I’m pretty sure is happening because RF from the antenna is being re-radiated by the house AC wiring. This will be a tough and maybe impossible problem to solve, as I am one tenant out of 10 in this house and don’t have access to the other tenant’s rooms.  There are a couple of solutions in my head, but they may not be possible given my current living situation.

The external antenna certainly does increase the coverage area over the supplied wire antenna. With the supplied wire antenna I could receive my transmissions all over the house, but not too far outside. With the external antenna coverage  seems to go as far as 1000 feet in some directions, but only a block or two in other directions. I don’t believe that this is in any way a fault of the transmitter but of my imperfect installation. I’m using a cold water pipe as a ground connection and don’t know how good a ground it is.  Although the antenna is about 15 feet off the ground, it is shielded on one side by the house and on another side by apartment buildings next door.  If I could mount the antenna on my roof I think I’d get better coverage (as long as I were able to ensure that the ground connection is not radiating in order to keep the FCC happy), but roof access isn’t too easy here.

I’d prefer to ground mount the transmitter so that I can ensure that the ground lead is very short and connects directly into the ground to avoid any possible misinterpretation of the ground lead rule if the FCC were ever to inspect, but ground space is limited on my plot and I have to be careful not to overstep any boundaries with my landlord and fellow tenants.

So…….I’m going to sit back and not do too much with this project for the time being. I may decide to use this transmitter with a short wire antenna just to broadcast around the house, or I may get another burst of enthusiasm and decide to try a different installation in the hope of increasing the coverage (and eliminating the hum on the carrier.)  It sounds great with a short wire antenna and I know that with the right installation it will sound great with an external antenna also. I’m hoping to cover an area of radius 3/4 mile around my house and I do think it can be achieved.

I’m also realizing how even my QRP ham radio activities are easier than Part 15 operation. With QRP, I run 5 watts and have no restrictions on antennas at all.  In fact, if I want, I can run up to 1500 watts on most ham bands into any antenna I want. Engineering a Part 15 system is truly a challenge.

Now if the FCC could just relax the Part 15 antenna restrictions and allow me to hook this thing up to an ATU and long wire antenna…………

July 2017 Update – Disillusioned by the lack of coverage, I sold this AMT3000, which I rather wish I hadn’t, but that’s another story. More recently, the urge came back to have another go at Part 15. I purchased a Hamilton Rangemaster AM1000E and am running it with a ground system consisting of two 8 foot ground rods, 20 feet apart, connected by a single buried radial. Coverage is now much better. Although weak, I can hear it intelligibly in some places up to a mile away. The primary coverage area seems to be about 1/4 mile radius, with the signal varying from weak to very strong within this area. My transmitter location is obscured by buildings and trees in some directions, which doesn’t make for even coverage. I tried an experiment running the same transmitter with no ground connection, and with very short audio and power leads, so that they couldn’t be acting as radiators, or somehow acting as a path to ground. The result was coverage of only a couple of hundred feet, before the signal dropped out completely. For this kind of installation, a good ground connection is very important. I’m not sure if I will publish a new post about this new Part 15 escapade, but my little station is running during daylight hours now, and shortly to go 24/7 as soon as I can acquire a dedicated laptop to run the programming on.

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