Dave Richards AA7EE

November 8, 2010

NT7S “Project X” Receiver In Action and 2 Meter FM In England

Jason NT7S just embedded into this blog post a YouTube video of the receiver section of his upcoming transceiver project in action. As a kid, I remember visiting the shacks of local radio hams and feeling the excitement to hear the sound of the bands on their “big rigs”. There was something about the rush of band noise coming through the speaker that was exciting to me.  It sounded even more compelling if reaching my ears through a narrow filter. Yes my friends, my name is Dave and I’m a licensed radio amateur. Anyway, Jason’s receiver sounds great, and flashes me back to those teenage moments.

The finished project will be available as a kit with a PCB and will be a transceiver.  Video of a QSO in action will hopefully follow once  the microcontroller is fully operational. Stay tuned.

My faltering steps towards improving the HF antenna situation here are temporarily halted while I prepare for a trip to England. On previous visits, I have usually taken my decent camera complete with flash, spare lens, filters, battery charger, spare battery etc. This visit is due to family health issues and I’m travelling light so that I am not distracted by all manner of electronic paraphernalia.  However, there will most likely be a few spare moments, so I thought I’d take a little 2 meter HT with me.  On a future trip I’d like to take a small HF rig so that I can work CW in England for the first time in over 25 years but the mission this time is not to be distracted by extraneous stuff, so this simple little HT is going with me:

GB3MH (for Malvern Hills), my favorite UK repeater, is no longer, so the radio is already tuned to GB3NW in the city of Worcester.

This radio is QRP even by 2 meter standards.  The output is 340mW on high power and just 50mW on low power. It uses 3 AA batteries that last for a long time – one set will be enough for the trip, negating the need to take a batterry charger.  If the batteries do run out, I can buy replacement AA’s almost anywhere. If the radio gets damaged, lost etc, used versions (it’s not made anymore) are cheap. It’s an ideal travel radio for some non-serious chatty FM fun.  The factory version of the model came with an integral fold-out whip antenna which in my opinion, was the weakest part of the radio. If you’re going to make a 2M HT with just 1/3w output power, why hobble it’s capabilities any more by including an inefficient whip less than a quarter-wave long?  I got mine from a ham who modified it for QRP mountain-topping by replacing the integral whip with an SMA connector to which can be screwed a light-duty quarter-wave whip, or other external antenna:

Back view showing modified SMA antenna connector and list of UK repeaters I hope to be able to hit.

I do very little 2 meter FM in the US. The chatter doesn’t really interest me, but I have fond memories of 2 meters (2 metres for my UK friends) in the late 1970’s when I was first licensed. I did a lot of chatting on the simplex channels and made some good on-air friendships. GB3MH, the Malvern Hills repeater, had very wide coverage, a fabulous signal, and was easy to access.  I could access it with one watt to a small paper-clip held in my finger.  I even tried a short length of wet string (really) once, and it worked.  I don’t know whether times have changed, or just me, but 2M FM just doesn’t do it for me now. However, I haven’t worked 2M FM in the UK since probably around 1982, so this will be fun. I’ll be in 2 places – the Redditch/Worcester area, and in the city of Bristol.  I have the following repeaters already programmed in:

GB3NW (Worcester)

GB3BM (Birmingham)

GB3WK (Leamington Spa)

GB3KD (Kidderminster)

GB3WR (Penn Hill, Somerset)

GB3WE (Bristol)

GB3AA (Alveston)

I’ll also be squirting my 1/3 watt of FM on 145.500 from time to time. If any UK amateurs are reading this (not sure if any do) will be in either of these areas and fancy a chat, then drop me a line.  I’ll also be in London for an hour or two and plan to listen to the London repeaters for a bit.

Next time I’ll take HF and pound some brass!

 

November 7, 2010

A Co-ax Trap Dipole For 40, 30 and 20 Meters – Or At Least That Was The Intention

Recently,  someone whose blog I follow mentioned that instead of waiting until a project is finished, he makes several mini-blogs about it, along the lines of  “New Blog Post – Soldered All Resistors in New Radio!”, New Blog Post “Now I’ve Soldered All The Capacitors!” etc etc. My approach has been to wait until a project is finished and do one big write-up on it, but now I’m having second thoughts.  I spent this afternoon putting up the first section of my new trap dipole and I’d like to blog about it so that I can get this part of the project “out of the way”, so to speak. Besides, I’m going to England next week and if I wait until the trap dipole is completely installed and working before I blog about it, it could be several weeks.

The 30M dipole that I put up a week or so ago works great, but I’d like to be QRV on more than one HF band.  The house I live in is shared with 9 other tenants and while I have a certain amount of freedom to put up antennas, I know that if I filled the sky above the house with wire, someone would object.  A dipole fed with balanced line was considered, but the feeder would probably be too intrusive.  I could tune a longwire against ground, but I preferred the idea of a balanced antenna for (hopefully) lower noise. It would also save me having to bang in ground rods and lay radials  – another move that my fellow tenants might object to. The coax fed 30m dipole that I just installed has not drawn any complaints, which got me to thinking that a trap dipole would also be fairly low-key.  It only has the one coax feeder, and the only thing that would make it stand out more than the current dipole would be the traps, which would be lightweight and fairly small anyway.

Having made lots of dipoles, but never a trapped antenna, I started by doing some reading on the subject (isn’t the internet wonderful?) Coax traps wound on thin plastic formers would be cheap and lightweight.  I did read that coax traps tend to be lossy near the resonant frequency so decided that for this reason, instead of putting the resonant frequency of the traps close to the desired operating frequencies, I would make them resonant below the bottom edge of each band in question. There’s no point in operating on a frequency at which your trap is lossy.

Another way to minimise the loss of an antenna using coax traps is to use the minimum length of coax needed to achieve resonance.  I let someone else do the math for me.  R.C.  Summer N4UU in his article “Optimizing Coaxial Cable Traps” in the December 1984 issue of QST,  says that the minimum length of coax will be used when the length of the coil divided by the diameter of the former is about 0.45.  Using VE6YP’s Coax Trap Program and some Nalgene bottles I picked up from the local outdoors/recreational store, I came up with the following for traps made with Belden 8259:

2″ diameter former – 5 turns of co-ax – resonant frequency 13.5MHz (length/diameter = 0.485)

2.4″ diameter former – 5.8 turns of co-ax – resonant frequency 9MHz (length/diameter = 0.475)

A lot of pill botttles are made of polyethylene, which has excellent RF properties (polyethylene is used as the dielectric in a lot of coax cables).  If you look at the bottom of the bottle, it will usually tell you what it’s made of. HDPE means high-density polyethylene, which is good.

Here’s the bottle for the 20m-30m trap, which I want to be resonant on about 13.5MHz.  I’ve already marked a line around the top with a Sharpie:

After cutting the top of the bottle off with a craft knife, I steady one finger against the end of the bottle to help in drawing a fairly straight line around the other edge:

A careful slice with the craft knife and – presto! – the former for our first antenna trap:

The coil has been wound and the center conductor of one end of the coax has been soldered to the braid of the other end, leaving one braid and one center conductor for connections to the antenna elements.  Notice the 3 small holes drilled in the end of the former to act as a strain relief for the antenna wire (there are 3 similar holes in the other end too).  I am not going to use nuts and bolts for the connections to the antenna as it adds extra weight – the antenna wires will be soldered directly to the traps:

Antenna wires soldered on and the whole thing covered with a good dose of Brush-On Electrical Tape. This is the finished trap, which resonated at about 13.2MHz:

For the center insulator, I decided to get rid of the SO-239 and PL-259. The traps will already add extra weight for the thin fiberglass mast to support – no point in carrying unnecessary weight. The braid and center  conductor of the Mini RG-8X were tinned and my new favorite goop, Brush-On Electrical Tape applied to seal the end of the coax:

The center insulator was cut from the lid of an old storage container.  It’s made of LDPE – low density polyethylene, and the whole affair looks strangely like some ancient fertility symbol:

This is stating the obvious to anyone who has built antennas before, but notice the loop of coax at the top, oriented so that any moisture will tend to run away from the end of the coax.

If the end of the coax were pointing upwards, moisture would have a tendency to sit on the end of the coax and would be more likely to creep inside. If this is your first antenna and you haven’t thought of these things before, notice how TV cables and electrical cables are looped or otherwise situated at the point of entry into a building, and then think of where moisture would collect.

I made the first two traps, which both resonated at about 13.2MHz, and fashioned the 20M part of the dipole thus:`

The idea with a trap dipole is to work from the center outwards, pruning dipole legs as you go, so my first objective was to get the 20M part working. I initially cut the 20M dipole legs to 17 feet each and found (with the MFJ-259B SWR analyzer) that the dipole resonant frequency was approximately 13.2MHz. At this resonant frequency, the SWR was 1.4:1 – not quite as low as I would like it. After pruning equal amounts off each leg, I got the resonant frequency to 13.975MHz with an SWR of 1.2:1 and a 1.5:1 bandwidth of 400KHz.

Next time I’ll trim about a little bit more off each dipole leg to get the center frequency close to 14.060. With a 1.5:1 bandwidth of 400KHz, I could place the center frequency at 14.175 and cover the whole band at less than 1.5:1, but I don’t care much about the phone portion and would rather cover the bottom 100KHz with as low an SWR as possible. Then I’ll add the 30 meter portion of the dipole and we’ll see how well these traps work!

UPDATE: – Next morning, I called CQ on 14060 and had a great QSO with WG0AT, who had been practicing the ukelele and said that his fingers were getting sore, so he jumped for the key to answer my CQ and give his fingers a break. What a thrill to have my first QSO with this antenna be with Steve, such a great QRP’er! Then I added the 30m section and noticed something that makes perfect sense, but having never built a trap dipole, wasn’t expecting. The addition of the 30 meter sections brought the resonant frequency of the 20m section down from 13.975 to around 13.55. Either the traps weren’t completely cutting off the outer sections, or there was some electrical interaction between the 2 sets of dipole sections, seeing as there was only an inch or so between the ends of the 20m sections and the beginning of the 30m sections. This is where trap dipole construction probably starts to involve a lot of pruning.  Also, the SWR at the new resonant frequency was 1.4:1,  so I was starting to experience the reality that a trap dipole, while able to operate on several different frequencies when correctly tuned, doesn’t give you as low an SWR on any of them as a simple one band wire dipole.

The light ran out, I didn’t get to finish pruning the 30m section, and then I made a mistake.  I decided to leave the antenna outside for the night with the traps not yet completely weatherproofed. That would have been OK had it been a dry night, but the heavens opened and it rained quite heavily all night. So I’m not sure that my traps are compromised, but if I were to go ahead with this idea, it would be best to wind new ones with fresh coax just to make sure.

All I need is a low maintenance HF antenna that will work on most HF bands so I can switch the radio on any time of day or night and operate. It is very apparent that antennas follow the same basic rule for all devices, mechanical and/or electrical, and that is that they can either do one thing very well, or lots of things less well, but not lots of things very well. It’s the reason computers are much higher maintenance than your standard AM/FM radio and it’s the reason that until I find a QTH more amenable to antennas I will keep fussing and futzing with attempts to be QRV on all bands 80 thru 10.

Here's one of the traps, with a liberal coating of Brush-On electrical tape on the turns to hold them in place. You can also the see the same product over the connections inside. Unfortunately, the center conductor at the other end of the trap hadn't been coated. Same thing with the other trap. Aah shucks.

 

With a trip to England coming up in few days, it’s time to shelve this project until my return, but I’m already not too happy with the trap dipole idea – too much fussing and pruning required to end up with an antenna that will be a compromise. I think my next step will be to put up a simple 40 meter dipole, which will at least give me 40 and 15, then perhaps another dipole connected to the same center insulator for one other HF band. I’ve also been wanting to try out an end fed dipole that was so well described in the October 2010 issue of World Radio Magazine Online (download it now before it’s taken offline at the end of the year.)

Bloody antennas.  Bane of my life.  If they weren’t so much fun I’d forget them and take up stamp collecting 🙂

November 5, 2010

Working FG5FR With 5 Watts

Filed under: Ham Radio,QRP,Uncategorized — AA7EE @ 4:28 pm
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Since putting up my new dipole on 30M I’ve been enjoying better performance than with my random (not very) long-wire tuned against what I thought was a ground but turned out not to be. In case you are wondering what on earth I was doing using a sub-par antenna, the answer is, well, I don’t really know.  Sometimes, as long as I can switch the radio on and hear something, I can make do with less than stellar antennas for quite long periods of time.

It has been very convenient having a dipole tuned for 30 meters. I’ve taken the Z11 tuner out of circuit and get a low SWR on 30 meters every time I transmit now.  It’s been so enjoyable that I started thinking it would be nice to have the same convenience on more bands. As a result I’ve started making some coaxial traps.  I’ve already made two that are tuned to about 13.5MHz (to isolate the ends of a 20M dipole) and will soon make a couple to resonate on about 9.5MHz (to go at the ends of the 30 meter section).  The result should hopefully be a lightweight trap dipole for 40, 30 and 20 meters. More on that in a few weeks after I return from a trip to England.

Back to my 30 meter operating, most of which recently has been a few enjoyable and leisurely QSO’s with other stations in western states. It’s always fun to hear a station’s surprise when I tell them I’m only running 5 watts – especially when they have just given me a good signal report.  On a clear channel you don’t hear much difference between a 569 and a 599,  especially with the receiver’s AGC turned on, so if a station isn’t listening too hard, you can sound much the same as someone running higher power.  However, I’ve had a few marginal QSO’s and a few that I’m pretty sure I only just missed, so I’ve been wondering whether to give in and actually consider running 100w. Next year I’d like to build the Elecraft K2, and the 100w option would help me turn those marginal QSO’s into solid ones. More on that in a future post.

Last night I was busy signing up for a Winlink 2000 account, downloading the necessary software, and trying to figure out how it all worked*.  The radio had been set to 10.106 for a few hours with not much coming out of the speaker.  The noise level on the band was around an S8 and I had grown accustomed to hearing this noise. Then the familiar sound of a station calling CQ….the station was not really strong but it was a clear channel and copy was not too hard. At first, my brain registered that it didn’t sound like a US call, so after his second CQ, having not copied a complete callsign, I sent “?”  He replied with “FG5FR FG5FR.”  Wow – he’d heard me!  I sent “FG5FR de AA7EE AA7EE AA7EE” and to my excitement he replied, gave me a 549 and told me his name (Fran) and QTH (Guadaloupe, which is an island in the Lesser Antilles). I sent him his report of 449, which he copied, thanked me and signed off.  I realized that I had forgotten to reciprocate by telling him my name, so I sent it twice, bade him 73 and signed off.   I’m not sure if he copied my name, but he did copy my callsign and signal report, so we have a QSO!

Not being a DX type, I don’t know whether FG5FR is particularly sought-after, but I do know that he is about 4,000 miles from me as the crow flies, he’s on an island in the Lesser Antilles, I worked him with just 5 watts to an inverted vee dipole, and I feel pretty good about that.  After QSO’ing with me he worked a series of stateside stations, so I guess I was lucky enough to get him when he was new to the frequency and first calling CQ – a very good way to snag DX, especially if you’re running QRP to a simple wire antenna.

*The Winlink software all ended up working fine, and now I know how to use this cool radio-based e-mail system for when I decide to start driving around the US in a camper van!

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