Dave Richards AA7EE

September 30, 2012

Building and Installing The Internal ATU, SSB Adapter and 160M Receive Options For the K2

F5VJD’s DSB80 is not completely finished.  I need to get rid of the chirp, and the first step will be to clear up some of my shaky grounding practices. I’d also like to build a sidetone oscillator. However, I spent a lot of time and put quite a bit of work into getting it into the case and wiring it up, and I really needed to take a breather before continuing with it.

In the meantime, Eric WA6HH posted a heads-up to the Elecraft reflector that there would be a slight price increase on several of their products in mid-September.  No more information than that was provided.  I knew that at some point I wanted to assemble several options for my K2 and, not knowing whether the options I wanted would be affected by the price increases, decided to go ahead and order them. As it turns out, mid-September came and went, and the options I ordered are still the same price but that’s OK – I wanted them anyway.

After working on the DSB80, assembling a few Elecraft K2 options would be a nice bit of relaxation. All I had to do was follow the instructions and everything would work – kind of like knitting a sweater according to a pattern. You do what they say and as long as you execute well, it works out perfectly.  That has been my experience with Elecraft so far, and these options were no exception.

The options I ordered were the K160RX 160M receive option, the KAT2 20W internal ATU, and the KSB2 SSB adapter. The 160M receive option was a bit of a no-brainer at just $40. I don’t do that well on 80 with my current antenna, so the chances of me doing OK on 160M are pretty slim, but one day I’ll be in the position to put up an antenna for 160M and on top of that, I was keen to see how far beyond the band edges I’d be able to receive – it was a way to increase the general coverage capabilities of the K2 just a little. Plus, the ability to have a different antenna for receive could be useful. The internal ATU would make operation simpler.  I’d been using an MFJ manual tuner, and wanted to be able to hop bands and frequencies more quickly (yes, lazy I know).

The SSB option wasn’t in my head when I first built the K2. I was so into CW, and loved the simplicity of a high-performance rig assembled solely with CW in mind.  However, very occasionally, I have heard stations on SSB that I wanted to contact. One station in particular was in the Philippines who was calling CQ with no-one coming back to him.  I don’t remember the band, but he was so loud that I knew he’d be able to hear even a QRP signal from me. It was one of those moments where I thought it’d be neat to speak into the mic and make an instant, easy contact with a DX station. Plus, even though I don’t use digital modes much at all, it would allow me to use WSPR occasionally if I so desired. I was also harboring a fantasy that I might want to start rag-chewing on phone one day but in retrospect, that was probably an unrealistic hope :-) As it turned out, the novelty of having SSB was starting to wear off after 2 QSO’s, and was mostly gone after the 3rd.  It’s still a good extra capability to have though, and I do like going through the process of assembling, installing and aligning circuits.

The K160RX 160M receive option is  a simple little board that doesn’t take long to put together, so I decided to have a go at it first. The board is upside-down in the first shot.  Sorry about that. Hmmm – looks like a couple of my foster cat’s hairs made their way onto the relay on the right-hand side. Those long-haired cats leave their marks everywhere…….. :-)   (Scroll to the end of this post to see where those hairs came from.)

Installation of this option is straightforward. On receive it tunes down to about 1600KHz, though with reduced sensitivity.  I’m not yet sure what the upper limit is. The board adds a 160M lowpass filter for the separate RX antenna, and switches in extra capacitance in the bandpass filter on the main RF board for 160M.  I’ve only heard one station on Top Band so far, though I’m sure the next Stew Perry contest will change that. Here’s what it looks like installed in the K2:

Looking from the rear (the plastic “boot” over the antenna connector is to remind the user not to use that BNC when the internal ATU is installed – it is supplied with the internal ATU kit -

Next up was the KAT2 Internal 20W ATU. This next picture of  the top-side of the partially completed LC board (the ATU is comprised of 2 boards) is posted here to illustrate a point.  I had a Twitter conversation recently with a ham who wants to build the K2, yet has a problem with his soldering generating a large amount of residual flux.  He couldn’t figure out why after soldering, his boards have so much flux on them.  I referred him to the Elecraft soldering guide and after reading it, he concluded that he was putting too much solder on his joints. This reminded me of Don W3FPR, who repairs and aligns a lot of K2’s, saying on the Elecraft reflector that he sees a lot of K2’s with way too much solder on them.  If you use a thin and mildly active solder along with a small tip on your soldering iron, you can easily regulate how much solder flows onto the joint, and ensure that you use the right amount and no more.  I use Kester RMA 285 in .02″ diameter (the RMA stands for “Rosin Mildly Active”.)  My tips are 1/32″ and 1/16″ diameter chisel tips – that’s 0.8mm and 1.6mm.   With boards that have plated-through holes, thin solder and a small tip will allow you to apply enough solder to fill up the hole and just a little more. From what I’ve read, ideally, you want to avoid a concave shape of solder in the hole – you should have a very small fillet of solder leading up to the lead, with the operative phrase being “very small”. I veer towards making the joint almost flat with the board – though flush cutters won’t allow me to make the joint totally flat. If you are applying the minimum amount of solder needed to make the joint, you wont have problems with solder bridging adjacent pads and causing unwanted shorts. You also won’t need to clean the flux off with a flux cleaner, because there won’t be much, and mildly active rosin isn’t corrosive enough to cause a problem if left on the board.  I think I did end up applying a little flux cleaner to this board eventually, but this picture was taken before applying it. What little flux there is, is honey-colored and hard to see in this picture, but I hope it illustrates the fact that unless you’re very particular about appearance, you don’t need to use flux cleaner if you’re using the right kind and amount of solder:

Another view of the top-side of the partially completed LC board:

Incidentally, if the board you’re soldering on doesn’t have plated-through holes, you will need to apply more on top of the joint in order to make a reliable connection. The capacitors on the above board are bent over per the instructions in order to achieve the necessary clearance. The underside of the LC board contains all the relays. If you look closely, you’ll see that relay K13 is not quite parallel with the other relays. These kinds of oversights on my part drive me potty but are of no consequence to the performance of the circuit:

I don’t have a picture of the whole of the top-side of the completed control board, but here’s a view from the side. It’s not a very good photo technically either but it’s all I have. Sorry about that. Note that the NPO cap behind the toroidal transformer is not the stock part (in case you were wondering why yours looks different.)  The stock part is a monolithic cap. I thought that I might have damaged mine (long story) so replaced it with this part. As it turned out, the stock part was fine, but as this NPO cap does a perfectly good job in it’s place, I left it in -

The finished KAT2 Internal 20W ATU:

At the bottom is the control board, and on top, the LC board, containing all the capacitors, inductors, and the relays that switch them all in and out of circuit when finding a match. The pink piece of foam underneath was simply to raise the ATU to the right angle to get a good shot.  I have become a bit lackadaisical recently, as I really should have looked for a way to support the board that wouldn’t be visible to the camera. I’m slipping.  Sometimes I just want to take the pictures and get to the next part of the project:

The completed unit showing the underside of the control board, with the 2 trim-pots that set the readings for forward and reflected power:

The KAT2 20W Internal ATU installed in the top cover of the K2. I’ve placed black electrical tape over the unused holes to prevent dust from getting into the K2.  My top cover was supposed to have been supplied with green tape over these holes, but it had already been removed when I received it.  Not a biggie:

Phew – only one more option to go – the KSB2 SSB adapter. I loved assembling the KSB2 board, as it is a little more densely packed than the K2 or any of the other options I had built so far. It’s fun building small things. Here’s the top of the completed board, showing all those lovely crystals (it’s a 7-pole crystal filter) -

The manual says to install the crystals flush with and tight against the board.  I usually try to build my circuits so they will be as reliable as possible and although there was an insulating solder mask on the top of the traces that connect to the crystal terminals, there was, in my estimation, the slightest chance that if the integrity of that solder mask were to be breached, there was a possibility of the pads being shorted out by the metal underside of the crystal casing.  It’s a long shot but why risk it if you can avoid it? I spoke with Richard at Elecraft who confirmed to me that if I were to space the crystals above the board by the thickness of a piece of paper, it wouldn’t adversely affect the performance of the filter. That was all I needed to hear, so that is what I did.

Although I have definite OCD tendencies, I do keep them in check on a regular basis.  Functionality is an important factor and although it’s nice to have all my toroids looking neat, I recognize that there is no difference in functionality between a toroid with perfectly spaced turns and the ones that look like mine in the picture below. Some of my toroids turn out looking really nice and some of them look just OK, but they all work just fine :-)  -

The underside of the SSB adapter board. RFC1 and RFC2, though marked on the underside of the board, are actually installed on the top-side. They are wound on very small FT23-43 cores and the only reticence I had about top-mounting them was that it was hard to avoid the windings coming very close to the metal cases of the adjacent crystals. I know the windings are covered in insulation, but I’m not overly keen on it. Unavoidable though. You can see how close the mini toroidal chokes are to the metal crystal cases in the direct overhead shot of the board, 2 pictures above. Here’s one of the underside of the board -

There are several reasons I post many pictures of my projects. I know there are times when I’m assembling something and I want to know how other people do it.  Occasionally, if an instruction in a manual is unclear to me, or can be interpreted in different ways, I’ll go trolling the internet to see what other people who built the same thing ended up with. Perhaps I can help a few people by offering up my pictures. Also, it’s fun taking pictures!

Before adjusting the carrier balance, the instructions in the manual say to place the wiper of the carrier balance trim-pot at approximately mid-travel. I did this and found that very little further adjustment was necessary to null out the carrier. I have only performed a rough adjustment using the S-meter of the K2 so far, but I’m pretty close.

All these options required a small number of modifications to the main RF board on the K2. Some builders who are reticent about desoldering components from their beloved K2’s have opted to use the Rework Eliminators.  I did think about it but decided against using them for 2 main reasons. Firstly, I’m cheap frugal and was already stretching my finances a bit even by buying just the basic K2. Secondly, I’m quite good at soldering and desoldering and don’t find it a nuisance at all to have to partially disassemble a rig and desolder a few components in order to fit a new option.  I have actually enjoyed the partial disassembly of the K2, as I got a chance to renew my acquaintance with it’s innards. The K2 PCB’s are high quality boards. You’d have to apply an awful lot of heat for a long time in order to damage them.  I did turn the flux darker in color in one or two places, but a quick application of flux remover with a plumbers flux brush took care of that.  The places on the K2 board where I have removed jumpers and desoldered components still look really good.

As a continuation of the last topic,  I hope you’ll allow me to air a few more opinions about soldering and the K2.  I do understand how someone who hasn’t built a K2 before would want to protect their investment. The Rework Eliminators are very appealing in this regard. In my opinion, they could be useful if you are going to be changing options a lot. Even a good board in the hands of an experienced tech will start to look shabby if soldered and desoldered enough times. Now that I have installed the 160M receive, internal ATU and SSB options, I doubt very much that I will need to remove them. If you’re experienced at soldering, the lack of Rework Eliminators  in my opinion is not a problem. If you’re not experienced at soldering, in my opinion also, you shouldn’t be building a K2.

Please don’t interpret the last sentence as a discouragement from building one of these absolutely brilliant rigs. If you have any inkling to build a K2 – please do.  It might be the last chance you’ll get to build this kind of a kit at the component level.  It’s certainly a classic of our times.  If you’ve ever thought that you’d like to build a K2 – definitely do it, but make sure that you can solder well before you start.  $740 plus tax + shipping (at time of writing) is a lot of money to spend on something if you’re just going to drown it in solder!

If your response to this is is something along the lines of “But my soldering isn’t very good and it’s always been that way” then I challenge you to improve it. It can be done.

As part of installing the SSB option, some extra components have to be installed on the control board – some capacitors, a couple of transistors, and a set of header pins for configuring the mic wiring for whatever mic you will use. For configurations that require adjacent header pins to be connected together, you can use jumper blocks.  The mic I decided to use was an old Heil Traveler headset.  I didn’t like the bulk of the thicker wire and adapter cord (that in my case was configured for an FT-817) and the small plastic box that contained a PTT button and freq up/down buttons, so I chopped it all off and got to decide how I was going to wire it to the 8-pin mic plug.  I decided to go with the straightforward configuration that the Elecraft MH2 mic uses i.e. adjacent pins connected to each other.  If I decide in the future to use any different type of mic, I’ll probably use a home-made adapter cable so that I don’t have to go into the K2 and re-configure for each different mic -

Here’s the KSB2 SSB Adapter installed on the K2 main RF board.  There is a hole in the SSB adapter board that allows the frequency counter probe to be attached to TP2, but I’m a little concerned that although it can also still make electrical contact with TP1, if I want to seat it fully into TP1, it looks like I’m going to have to file some of the edge off the KSB2 board -

Those blank holes on the back of the K2 are starting to fill up.  The blank holes are supposed to be covered with green masking tape as supplied, but that tape had already been removed on the covers supplied to me, so I have covered the few remaining holes with black electrical tape. Looks OK and keeps the dust out -

I’ve had a few SSB QSO’s with the K2 so far and out of 5 QSO’s, 4 of the stations gave me unsolicited reports of excellent sounding audio. One station said that perhaps I could use a few more highs and a little less on the low end, but that I should be careful about messing with the audio too much as it already sounded very good.  I may adjust the carrier placement in the filter pass-band just a little to accentuate the highs, but I think I’m pretty close.

Assembling and installing these options has been an enjoyable exercise.  It has given me the opportunity to re-familiarize myself with the insides of the K2 and has only solidified my liking for this rig, as well as my respect for Elecraft. The ham community is very lucky to have this company making these great products for us.   My budget has taken a bit of a beating this month, but I’m hoping to be able to get the K60XV 60M option pretty soon :-)

Oh – and those hairs on the relay in the very first picture in this post? They came from Chala – a 10 year-old kitty that I’m fostering right now. There is a group that goes out every night and feeds the feral population here in Oakland. Chala was amongst those cats, but one of the volunteers brought her into the shelter because she was not doing at all well on the streets. She’s a shy kitty with a very sweet nature, and was unable to defend herself from the other cats. She was in really bad shape when first brought into the shelter, but is slowly starting to settle down and get comfortable here. She’s a sweetheart and as you saw from the photo of the K160RX option (if you were looking carefully), is already starting to leave her mark on my construction projects :-)

Chala is pondering how the K2 will perform on 60M when I build the K60XV option.

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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This loading coil is BEEFY.

 

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…………

 

 

May 27, 2010

A Different Type Of QRP

My radio interests have taken a different course in the last month or so and I’m not sure whether it’s appropriate to include them in this blog or not, so let me tell what I’ve been up to and you can decide;  I’d welcome your comments.

I had been earning my living as a DJ/announcer/voiceover guy since 1987 until last year when the paid work all came to an end for me. I really thought I’d gotten over the DJ bug and in some ways, I think I have.  As a youngster, I very much wanted to prove myself – to both myself and my peers.  Being perfectly honest, there was a need for a certain amount of ego gratification too. Well, I don’t feel the need to prove myself to anyone anymore and as for the ego gratification part – well, I think that age has cured me of the need for that.

But interests picked up at an early age never go away completely and so it was that a month or two ago I became interested in setting up a Part 15 AM broadcast station.

Most people reading this blog will know about the FCC regulations that cover Part 15 devices, which can be broadly divided into 2 types – non-intentional radiators and intentional radiators.  Non-intentional radiators are devices that emit RF as a by-product of what they do and then happen to leak some of it. This category includes the local oscillators of radio receivers and the crystal controlled clocks in computers, for example.  Intentional radiaters are devices for which the RF radiation is the main point of the device.  Baby monitors,  cordless phones and garage remote controls are examples of intentional radiators.

Part 15 regulations also cover something which is quite attractive to me,  and that is the ability to operate a low power unlicensed yet completely legal broadcast station. On the FM broadcast band, there is a strict field strength requirement at a set distance from the antenna that makes it unlikely you’ll be able to achieve a range much greater than 200 feet.  This is fine if you want to play music from your iPod on your radio, but you’re not going to build much of an audience with a Part 15 FM station. The criteria for transmitters on the AM broadcast band are much more lenient; instead of field strength measurements at a specified distance from the antenna, the main rules are that the input power to the final amplifier cannot exceed 100mW and the total length of the antenna and ground lead cannot exceed 3 meters.

100mW to a 10 foot antenna on the AM broadcast band isn’t much, but if you engineer the whole system for maximum efficiency, it can be possible (from what I’ve read) to achieve a range of up to a mile (or even more) from the transmitter. What makes this even more appealing is that the FCC allows the use of multiple transmitters to increase coverage. Place a few transmitters around the edge of your primary coverage area, and now you’re starting to cover a significant part of a city.  Some small town residents can cover a significant part of their entire community with one well-placed transmitter. The same discipline of maximizing the efficiency of the whole system that applies to QRP ham operating also applies to Part 15 AM operating. After all – it is also QRP. In fact quite a few operators of Part 15 AM broadcasting stations are licensed hams.

Many Part 15 AM broadcasters are either people who want to broadcast old-time programming to their restored antique radios, or Realtors with their “Talking House” transmitters broadcasting details of houses for sale to prospective buyers parked outside.  A smaller, but very enthusiastic subset of  Part 15 AM operators are the folk who run their own radio broadcasting stations.  The FCC don’t recognize these outfits as radio stations; they are simply classified as intentional radiators.

At this point, you’ve either completely tuned out or have at least some level of marginal interest. Here’s a picture to break the monotony:

 

Ant Radio broadcasting from the Pill Hill district of Oakland, California

 

Not a great photo I’m afraid.  At some point I’ll take a better lit and processed picture, but at least you can see what it looks like. This is where I do my ham operating too.  In the shelf unit to the left is the FT-817,  KK-1 straight key and Bencher paddle along with the Fort Tuthill 80 and 2N2/40 as well as my soldering station, 13.8V regulated power supply – oh, and my DVD player to boot! There is also my Signalink USB sitting on top of the Tut 80.

On the right is AM broadcast central. At the bottom is a Mackie mixer on a pullout shelf. Above it the Denon dual CD player (2 separate units – the control unit at the bottom and the CD trays in the unit above it.) The microphone is an EV RE27N/D. There is a Shure SM7 (also on a boom arm) out of sight of the camera for guests.  At the top of the rack are the 2 audio processing units.  The lower one is the first in the audio chain after the mixer.  It is an Aphex compellor which provides compression, leveling and peak limiting of the signal. Above it is an Inovonics 222 which provides pre-emphasis, a lowpass filter (to limit the bandwidth of the transmitted signal) and more peak limiting. It supports asymmetrical carrier modulation to modulate the transmitter to as much as 130% – another way to maximize the range of this QRP signal. The Inovonics 222 is quite popular with AM amateur radio operators to help them squeeze maximum efficiency from their signals.

If you have any interest in this, I thoroughly recommend Hobby Broadcaster (link opens in a new window) – the site for Part 15 AM and FM broadcasters.  It’s run by broadcast engineer Bill DeFelice who also actively participates in and moderates a great set of forums. There are other sites that deal with Part 15 broadcasting,  but Bill really sets the tone in his forums with helpful friendly comments and advice as well as equipment reviews.  He also posts his online finds for those who are looking for deals on good affordable gear for their stations.

When I’m not DJ’ing live (which will be most of the time) the computer runs the whole station in automation and so far, it’s not sounding too bad at all. I’m currently spending a lot of time recording and producing all the station ID’s as well as adding to the song library. When Ant Radio hits the airwaves, I’ll probably post an air-check so you can hear what my little broadcast station sounds like.

Maybe I’ll even get the occasional DX report :-)

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