In contrast to my field day adventures last year, in which I hung out with the folks from the North Shore Radio Club and ran 100W on a K3S, this year I opted for a decided more small-scale approach. Using my ATS-4 receiver, I ran 3.5W CW on 15m, 20m, and 40m for about four hours Saturday afternoon in the lakefront park here in Chicago.
My antenna was a single 40-some-odd-foot wire hung from a tree, fed by my ZM-2 antenna tuner. I think when I built the ZM-2 last year, I goofed something up in the SWR circuitry – the built-in LED should go out at minimum SWR, but mine seems to be brightest at low SWR. To compensate for this, I brought along the MFJ-207 Antenna Analyzer I got at the SMCC Hamfest last year and used that to adjust the antenna tuner.
With the big analog, multi-octave dial on the front of the 207, I found it useful to first tuner the ATS to the desired frequency (say, 14.030) while attached to the antenna and adjust the analyzer until I heard the “WHOOP” of its signal generator in my headphones. With the frequency of the analyzer and receiver close to matching, I’d move the coax back from the tuner to the analyzer and adjust the ATU until the 207 showed lowest SWR. Reconnect the ATS, and away we go!
I used a new battery setup for this outing – a 12V, 6000mAh TalentCell lithium-ion pack that I borrowed from work. I love this pack – a little less than a pound, charges from a wall-wart, and has a built-in barrel connector and on-off switch. There are also models with a built-in 5V USB charging port, for topping off cell phones and other devices on the go. While the ATS is designed to run at 12V MAX (not 13.8V), I found that the 12.2V the pack was putting out proved to be fine – it seems the limitation is in the heat dissapation from the BS170 finals, and running relatively low duty-cycle search and pounce that wasn’t an issue. I’ll be ordering one for my own use soon. (Or perhaps the even more compact 3000mAh version – the size of a deck of cards!)
The rest of the pack list included:
A HamKey brand iambic paddle
A golfball and a kite-string winder for getting the antenna wire into a tree
A small battery-powered speaker with 1/8″ aux input
Variable DC and Coax jumpers
A notebook and pen
A folding camp chair.
All of the above fit into a small laptop bag, along with a few other tools and bits I didn’t end up needing.
I managed 69 contacts, all QRP CW hunt-and-pounce, during my operating time – no tremendous DX, but I did hit a couple of rocky-mountain states and a plethora of sections up and down the East Coast. Final score was just over 1000 pts – that QRP multiplier really stacks up!
I also couldn’t have asked for better weather on the day – 72 degrees and slightly cloudy with a pleasant breeze. Simply stupendous.
Having put up a basic wire antenna last week, I thought I might as well give it a spin over the weekend to see how well it might receive on the various bands I have access to. This being the weekend of the California QSO party, I figured there would be lots of big signals on the air to try to hear.
Much like when I first put the QST-49er on the air, I had much higher expectations for reception that for anybody else hearing me, but I was to be proved wrong. Using the ATS-4, my power output is about 3W on 80m, 40m, 30m, and 20m, and about 2W on 15m. I figured I would find the strongest calling stations that I could and use them as a gauge of where I was receive in signals from.
Much to my delight, the CW portions of both the 20m and 15m bands seemed to be filled with California stations calling “CQ CQP” (California QSO Party). Some of them S7, a couple over S9 even with my simple antenna. With no AGC, some signals were strong enough as to require me taking the earbuds partially out of my ears. With propagation and the antenna seeming to cooperate, I quickly looked up with CQP exchange (serial number and state) and responded to some of the CQs.
And do you know what? Not one, not two, but twenty-four different stations came back to my little QRP signal. Twenty Four! In the span of a Saturday afternoon (and one more Sunday morning) I increased my lifetime QSO count by almost %500, including my first 15m contact (K6LRN), my first 20m contact, and my first CA contact (both N6CK in Poway, CA). Here’s a map of as many contacts as I could grab Lat/Long data for, all up and down California:
One of Eric Guth’s guests on the QSO Today podcast (and I can’t for the life of me find who) expressed that the joy of radio sport for him was that he got a little spark of joy every time he made a new contact, and that contesting gave him that feeling hundreds of times in a row. While I didn’t hit hundreds of times, I certainly felt the rush of making contest contacts, fighting to be heard with other stations, the victorious feeling of finally being heard, the reward of persistence…. I could get into this radio sport thing.
If that’s going to be an area of interest, I’ll need to practice a little more on my reception speed, especially when it comes to numbers. For this contest, I would often listen to the California station go through two or three other contacts to try to pick out the serial number he was on and his county before I’d make a call myself. My receive speed just isn’t high enough to go into a contact from scratch. But I’m grateful to all the ops who were willing to slow down and repeat themselves when asked. It made me feel very welcome as a new op.
In any case, my claimed score for this one was 1224 points, distributed like so:
I suspect my actual score will be much less than that. I know I botched a couple numbers early on, and even gave out the wrong number once (oh the shame). But even if I only get one point in the log, that’s good enough for a first time out.
Sometimes the simplest of radio work pay the biggest dividends. Last week, after a few weeks of hemming and hawing about it, I finally committed to putting up a longer wire antenna that allowed the possibility of using multiple bands. The 40m dipole I put up at the end of August has proved to be fine as a receiving antenna, but it suffers two key limitations. First, it’s obviously a single-band antenna (though I may try it on 15m as well). And second, situated as it is between two apartment buildings, I think I’m wasting most of my energy heating up the bricks rather than propogating energy out into the world. It’s also only ~10′ off the ground.
The new antenna helps with all of these issues. It’s simply a ~58′ piece of 22-gauge speaker wire strung from the office window out to a tree that sits in the apartment’s back yard.at its highest, the wire is maybe 20 feet up. While it’s a little visible in the alley if you’re looking for it, it blends in with the surrounding tan brick enough that I don’t think it’ll be noticed. I dropped a ~16′ piece of the same wire out the window to act as a counterpoise.
No, I swear, there’s an antenna running right through the center of this picture.
Like any random-wire, this one needs a tuner to be useful. I first tried using the ZM-2 tuner I got last Christmas. I sadly think I have a short in one of the variable caps in that tuner, which makes it non-functional for now. The MFJ-949e tuner did the trick though – I attached the long wire directly to the “WIRE” banana jack on the back, and the counterpoise to the grounding lug. The antenna tunes up better than 1.2:1 on 80m, 40m, 30m, 20m, and 15m. Which doesn’t necessarily mean it’s an efficient antenna, just that it won’t unduly stress my transmitters.
When I tuned the antenna the first time, I made myself a cheat sheet of the capacitor and inductor settings that gave me the lowest SWR on each band. I then taped this cheat sheet to the top of the tuner. This gives me a place to start when I need to retune for a particular band.
The same evening that I put the antenna up, I did a tune-through of the CW portions of 15m, 20m, 30m, and 80m. It’s really the first time I’ve been able to hear anything on a band beside 40m, so I figured a little exploration was due. I came across an S7 signal at 3.545 MHz calling CQ, and just for grins, I gave him a call. And he came back to me! Arthur, N8ART in Columbus Ohio, running an older rig into a dipole, if my copy was right.
Columbus is a little under 300m from my QTH in Chicago, so this was probably a single-hop contact, or really NVIS. But it represents my first contact outside of 40m, which is terribly exiting! The new antenna is already proving its worth.
This was also my first contact with a new transceiver, an ATS-4 which I snagged as a “tech-special” (i.e. broken) from qth.com and repaired. That process deserves its own write-up. I’m also using a second-hand Ham Key I picked up at Radio Expo 2016 in Belvidiere, an event that also deserves its own post. But really, I’m just too excited about the contact on a new band to try to keep these posts strictly sequential.
Up to this point, if I wanted to get on the air, I had three antenna options:
Walk 20 minutes to the lake, spend 15 minutes getting a 40m inverted-V set up in a tree, and hope I didn’t forget anything. This has been netting me good results, but is a bit cumbersome.
Set up the PHF40 loaded-dipole antenna on a tripod in the backyard. Also a bit cumbersome, and I’ve not had any success making a contact on that antenna yet. I suspect the efficiency is quite a bit down from a full size antenna.
Try the random-wire I’ve got strung up around the office.
While it certainly doesn’t feel like it in the August heat, winter is surely coming. In order to ensure I won’t have a long operating hiatus once the snow hits and going outside is impossible, this week I set about putting up a 40m dipole in an inconspicuous place.
I won’t share exactly where the antenna is mounted, but suffice to say all parts of the antenna are about 12ft off the ground – much more of a skywarmer than a DX antenna, I should think. I tuned this antenna the same way I did with my inverted-V, using just the MFJ-207 and a pair of snips.The antenna ended up being 31’6″ along each leg.
The final antenna is resonant around 7.075 Mhz with an SWR of 1.2:1 at that frequency, with a 2:1 SWR bandwidth of 6.9-7.240 Mhz.
Currently, the feedline is just a piece of RG-58 sneaking in through a window into the apartment. Interestingly, the SWR at resonance shoots up to 2:1 if I bring the metal window-frame down to within about an inch of it. I should note that I’m not using a balun with this dipole, just the usual center-conductor-to-one-wire, shield-to-the-other setup, so it doesn’t surprise me that the coax is coupling to the window. I’ll need to set up some kind of non-metallic passthrough to block airflow with maintaining the antenna characteristics.
After a couple evenings of listening, all signs point to this being a workable antenna! The map below shows the stations that I’ve heard (not contacted) in the past couple evenings. The station in red is one that I was able to contact, but we were fighting QSB and couldn’t really complete the QSO.
Today, for the first time, I reached out into the ether on HF, and had someone reach back! All with three Watts and a wire. I’m still in blog-post-debt for both field day and the new transceiver, but I’m just so excited, I’ll drop this in as quickie post for this evening. It’s not a proper QSO, but it’s as close as I’ve come yet.
(A small caveat – I’ve worked a couple field days, one with WVARA in Silicon Valley and now one with NS9RC in Chicago, but someone making rapid-fire contest contacts on somebody else’s very shiny K3 doesn’t feel like my contact, you know?… I’m still counting this as an emotional first.)
I had a 40m inverted-V thrown in a tree by Lake Michigan like I described in my previous post. I’d been listening an tuning around from about 7:45pm local time, throwing out the odd CQ, trying to tail-end some conversations without much luck. I’ve been hanging out mostly around 7.110-7.114 MHz, which are both a slow-code area and the area near the SKCC calling frequency, which seems to attract patient and friendly code operators. Finally, around 9:25pm, I heard a very, very slow “CQ CQ” right on 7.114 MHz. The call was from W4JWC, I suspect from a keyer – it was very slow and regular, and easy to copy. I shot him back a quick “W4JWC de KK9JEF,” and he came back! Still slow, medium-signal but with some serious fading.
Here’s the entire text of my first contact. I’m including it, not because it’s particularly interesting, because I think I’ll enjoy looking back on it later:
CQ CQ CQ CQ de W4JWC W4JWC K
W4JWC DE KK9JEF KN
KK9JEF DE W4JWC UR RST IS 539 RST 539 NAME IS JERRY JERRY QTH WIRTZ VA WIRTZ VA KK9JEF DE W4JWC K
FB FB JERRY NM HR IS JEFF JEFF QTH IS CHICAGO IL CHICAGO IL HW? HW? W4JWC DE KK9JEF KN
KK9JEF DE W4JWC QSB QSB SRRY SRRY DE W4JWC K
W4JWC DE KK9JEF YES QSB QSB UR RST 539 539 W4JWC DE KK9JEF KN
KK9JEF DE W4JWC QSB QSB SORRY QSB DE W4JWC K
The key thing to notice in all this is the Q-signal “QSB,” which denotes fading. In addition to dealing with general noise on the bands, both man-made and natural (including static-crashes from lighting), signals can also fade-in and out, just as if someone was playing with the volume knob. One moment the codeis loud and present, the next it just fades into the sonic underbrush. Frustrating, to say the least.
I’m calling this my first HF “encounter” because I don’t think Jerry will have copied any of my information – typically, it seems, an HF contact or “QSO” involves the exchanging of signal reports (RSTs), names, and locations (QTH). Since Jerry didn’t get mine, I don’t think I’ll be in his logbook, and he isn’t officially in mine. But he’ll be remembered here, as the first key from the airwaves to respond.
So much has happened radio-wise in the past two weeks, and I’ve been quite delinquent in updating the blog. This post won’t even get to Field Day, nor my new transceiver, but I’ve got to start somewhere. So let’s get to it!
Using the MFJ-207 antenna analyzer I picked up at the SMCC Hamfest a couple weeks ago, I’ve now set up tuned, worked with, and taken down a 40m inverted-V four or five times now. Since space around my apartment is limited, I’ve been walking the 15 minutes out to the shores of Lake Michigan. The lakefront has ample trees and open space to erect an antenna without being too much in anyone’s way.
The first day I set up the inverted V was the most exciting, and went something like this. I took my dipole-kit out to the lake, which contains 200′ of thin nylon rope, a dipole center, a couple equal lengths of 18-guage speaker wire (35-ish feet each), two weights filled with rice to throw into trees, and three 8″ pegboard hooks. (The hooks make excellent ground-spikes to tie off the ends of the nylon rope. I picked up a bunch at Menards when they were on sale for 20 cents each.)
In addition to the antenna parts, I’ve been taking along a small SLA battery and powerpole adapter, a 25′ bit of RG-58 Coax, a homemade “ugly balun” (see below), the MFJ antenna tuner, a radio, headphones, a pad of paper and a pen. The heaviest parts of the pack by far are the SLA battery and the the two coax items. I’ve also sometimes brought a portable camp chair so I don’t have to sit on damp grass… but lying in the grass in the summertime isn’t bad either.
The process of putting up the antenna is straightforward. I unpack the kit and lay out the parts under a suitable tree. I throw one of the weights with a rope as high over a branch as I can, then tie the dipole center to the loose end of that rope. I lay out the two antenna wires roughly on either side of the center, and attach both wires, the ugly balun, and the coax to the dipole center. Once everything’s attached, I haul on the rope to raise the dipole center up as high as it will go, and tie the working end of the rope around a stake just under the center of the antenna. I walk the wires out as far as they’ll go (each now has maybe 5′ of nylon rope attached to the end), and tie them to stakes as well. The whole process takes between 10 and 15 minutes and is getting faster every time.
The first time I put up the inverted V was enlightening, to say the least. I attached the ends of the antenna wires directly to the ground stakes, and hooked up the MFJ tuner to the other end of the coax. The MFJ207 is essentially just a wideband oscillator with a 50-ohm output, with a built-in SWR meter. You tune across the frequencies of interest (in five separate ranges, see the MFJ 207 Manual for technical details) and read off the SWR on the analog meter. In this case, I was hoping to see a nice dip around 7MHz. Though that’s what the picture below shows, it was quite a process getting there.
The first time I put put the antenna, it showed a clear dip… but a little under 5 MHz! To be sure this wasn’t just an issue with the calibration of the analyzer, I plugged my cheapie Ebay 8-Digit Frequency Counter (“Cymometer”) into the frequency-measurement port on the top of the analyzer. It read 4.87MHz. Dang. My antenna was definitely too long.
As a starting estimate of how much to trim the antenna, I did a quite back-of-the-envelope calculation of how “electrically long” it currently was. Taking the speed of light to be roughly 3 x 108 m/s and dividing by our resonant frequency of 4.87 MHz gives a wavelength of 61.6 meters, which means each quarter-wavelength wire of the dipole is about 15.4 meters long. To work on the 40m ham band (7.0 to 7.3 MHz here in the states), let’s say the antenna wants to be resonant around 7.1MHz. Similar math to the above gives a wavelength of 42.2 meters (surprise!), or about 10.5m per wire. By this math, the wires were about 5m too long.
However, there are many factors that can cause an antenna’s resonant frequency to be lower than it would be in free space, and one of them is proximity to the ground. Not only was the antenna’s center only 6-7 meters feet above ground, but the ends of the antenna were literally touching the ground. Given these factors (and the fact that while I had cut the wires longer than necessary, I didn’t think they were that much longe), I decided to be conservative in the my trimming. What’s more, I left the ground stakes where they were, and replaced the trimmed sections of wire with nylon rope. In other words, the angle of the inverted V didn’t change as I trimmed the wires, only the length of the wires themselves, and therefore the height of the ends above ground.
With an eye toward being conservative with my trimming, and knowing that the math would have me trim 5 meters off the antenna in free space, I instead opted to trim 5 feet off each wire instead. This left each end of the antenna about 2′ off the ground, instead of touching it. After this brief surgery and re-attaching the nylon rope, the MFJ meter proclaimed the antenna resonant at 6.46 MHz. Now that’s better!
Another quick snip of 18″ on each end got the antenna resonant around 6.75 MHz, and another 15″ off yielded resonance at 7.097 MHz. For these measurements, I tuned the analyzer for lowest SWR, then measured the frequency with the frequency counter. In future, it seems like the dial measurements will be good enough for daily use, but for dialing in the antenna the first time, the frequency counter was very helpful.
To get an idea of the useful bandwidth of the antenna, I also swept the frequency up and down around the resonant point and took some frequency measurements. The antenna had better than 2:1 SWR between 6.922MHZ and 7.282 MHz. Pretty much all of the the 40m band, and certainly the CW portion that I plan to most immediately be working.
All in all, I consider the several outings this week to be great successes. The MFJ is surely worth the $15 I paid for it. I was battling some dodgy coax the first couple times out, which made it hard to take SWR readings without the needle jumping all over the place. A little Amazon order of some RG-58 fixed that. Now, I’ve got a working, tuned, successful antenna.
One more thought: the so-called “ugly-balun” or air-core choke. Mine is simply 25′ of RG-58 close-wound on 10″ of 1.5″ PVC pipe, secured with zip-ties and duct-tape.
When using a dipole without a proper center balun (that is, an actual transformer that forces equal and balanced voltages on the balanced side from a single voltage on the unbalanced side), the dipole essentially becomes a “tripole”, with the outside of the coax shield possibly becoming part of the antenna and carrying RF. I say possibly, because it will vary with the length of coax between the transmitter and antenna feedpoint. This is undesirable, because we’d like the antenna itself to be the radiating/receiving part of the system, and not be depending on the physical arrangement/length of the coax itself.
One solution would be to install a proper balun (sometimes called a voltage balun) at the center of the dipole. This forces the voltages to each leg of the dipole to be equal, thereby eliminating common-mode current on the outside of the coax. However, a choke can also reduce current on the outside of the coax. For this reason, the coke is sometimes called “current balun” or “choke balun,” though strictly speaking it isn’t a balun at all.
Here’s a quote from one of the links above:
A choke is not a balun in any way. It’s given that description, ‘balun’, because it can do something a balun can also do, get rid of unwanted currents (CMCs) on the outside of the coax feed line. It can’t transform from a balanced to unbalanced state. – ‘Doc
There’s lots of other useful information in that same thread, which I find myself returning too and musing over. It seems, long term, that a ferite balun is really the way to go for choking off stray RF, but in the meantime, adding the air-choke to the antenna feedpoint does seem to help somewhat. I’ll continue throwing it in my pack and experimenting in the meantime.
Today, I received a package in the mail from a fellow ham who was getting rid of some gear. Specifically, he’d put together most of the parts to put an Arduino-controlled VFO on one of the cheapie Chinese Forty-9er kits, like Farrukh Zia did in a QST earlier this year (his kit is available online.) The package I received had the Zia board, an Arduino Nano, an AD9850 DDS module, a rotary encoder, and the Forty-9er kit itself, already assembled. I do want to someone assemble the kit as described in QST, but for the moment, what I’d really like to make is an antenna analyzer.
The scope of what constitutes an “antenna analyzer” is wide – from my rinky dink setup at the bottom end to 4-figure solutions at the high end. Really, what I’ve put together is andirectional coupler with 50-ohm terminations. The fancier analyzers will tell you not only the actual impedance of the antenna (or anything else on the output port), but also the magnitude (and in some cases the sign) of the reactive component of the impedance. Neat stuff! For my purposes, a simple Arduino-driven device that measures relative SWR will be good enough for my purposes. (Dan, KB6NU, has a helpful write-up of some of the mid-range options.)
I’ve been looking at K6BEZ’s plans for an Arduino-based analyzer for a long time – really, the key piece I thought I was missing was the AD9850 – and this seemed like a good time to give it a try.
I had an SWR Bridge Kit from KitsAndParts lying around, and I thought this would be a good time to put it to good use. The kit is simple directional coupler, with a couple diodes and capacitors in each line to hold a peak DC level. The coupler is meant to drive a pair analog meter movements.
To adapt this coupler for use, I first simply attached each output to the Arduino’s analog inputs. This went quite poorly – the charge building up on the capacitors on each side of the coupler has no where to go, and so rather than giving an instantaneous peak voltage, the analog readings just kept creeping up and up. A 68K resistor from each output to ground (facilitated by a small breadboard) solved that issue.
The main issue now is one of scale. The AD9850 Module itself puts out a little less than a milliWatt at most, deceasing with higher frequency outputs. The K2ZIA module has a little two-transistor cascade amplifier to help compensate for this, but that only pumps the output up to 14 or 15 dBm at 1 MHz, with decreasing returns at higher frequencies. Given that the directional coupler has a “single turn” (1 wire) pickup through the center of each toroid, and each toroid has 12 turns, we can surmise that less than 1% of the energy going into the coupler is being diverted to measurement functions. with the rest passing through to the antenna.
This low amount of coupling would normally be desirable, but this time, that means -5 dBm presented to the FWD measurement port, which just isn’t enough power to overcome the forward voltage of 1n5711 diodes in the coupler. (I measured mine to have a voltage drop of 0.323V. That’s which a $50 multimeter, so take it with a grain of salt, but that’s the order of magnitude.)
To temporarily overcome this, I hooked up my little BS170 board from the Si5351-Amplifier to the output of the K2ZIA board’s amplifier, which gives me about 4W output at 1 MHz (and decreasing above that). This gave me enough power to test the coupler (and the K6BEZ software), and both seem to be working fine. I’d like not to build another 5W amplifier just to use as an antenna analyzer, though, so once a shipment of 1n5711’s arrives from eBay, I’m thinking of just replicating K6BEZ’s detector circuit, using a resistive bridge and op-amps.
I’ve been trying to think how long its been since I’ve been to a ham radio swapmeet. Certainly the last one I visited was the Electronics Flea Market at De Anza College with W6KWF sometime during my college days. So it’s been a good long while, and it seemed time to rectify that. And thus, I’m just back from the DeKalb Hamfest. First some details, and then I’ll get to today’s haul. A bit of a long post today, but there’s much to tell.
A brief overview – the DeKalb Hamfest is hosted by the KARC – the Kishwaukee Amateur Radio Club – and overseen by Bob W9ICU. It’s hosted at the Sandwich County Fairgrounds in Illinois around this time (early May) each year. $8 for admission, and easy parking.
It wasn’t a huge event – maybe 10 or 12 indoor vendors and perhaps three times that many tailgate-ers. The indoor vendors, while they had lots of nice products, didn’t particularly entice me, as I think you could find just as good value on, say, banana-jack-to-BNC tails or audio connectors anywhere online. There was one vendor with a huge spread of every RF adapter and then some, as well as individual toroids for sale, including some big 100- and 240- size ones in unusual mixes. I’ll look for them at future fests.
The tailgate-ers were more my speed, though none of the big-ticket items were really what I was looking for (or in my price range) Several old Heathkit receivers and transceivers for sale ($200-$600), lots of microphones, mobile units, CB radios. A few newer items, but mostly old tube equipment. At least four tables had the same Heathkit GD-1B Grid Dip Meter, which I found curious. Lots of vibroplex keys marked over $100.
But lots of treasures too. Maybe only three or four tables with proper parts bins, but I spent a good couple hours pouring through these to find some treasures. Most table owners were happy to make small talk and chat about their projects and where their goodies came from. I had a really laugh chatting with some of the nice folks running the tables, while piling up the day’s haul.
And what a haul!:
Here’s the short list, starting at the bottom-left and working clockwise:
A pack of five unlabeled compression trimmer capacitors. These turned out to have a range of about 2-25pf.
A bag of ~10 small toggle switches with assorted mounting hardware. These range from SPDT to DP4T.
A large bag of ~20 rotary pots of assorted values, with a few rotary switches thrown in for luck.
A couple RG-58 jumpers with BNC connectors (free!)
A large air-spaced variable capacitor – unlabeled, turned out to be about 28-152pF. More on this below.
A nicely boxed step-attenuator with 50-ohm input/output impedance. I’d been thinking about building one of these, but running across one of them at the fest (for only $3) was a dream! It has a maximum of 59 dB of attenuation in steps of 20, 20, 10, 6, and 3 dB, as well as a variable attenuator (“3 dB?”) for fine tuning. It has Walter Schwartz’ name on the bottom, who was the nice gentleman who sold it to me. A very cool older ham.
A mysterious silver box… more on this below as well.
A bag of twenty 47pF NP0 capacitors. For future oscillators.
A couple bags of trimmer pots. One bag had five 500 Ohm trimmers, the other turned out to have a mix of 1K and 1M trimmers. I have these in mind as balance pots for diode mixers, but we’ll see where they end up.
A couple vacuum-molded packs of trimmer capacitors, 10-. These actually came from the Fry’s Electronics in Downer’s Grove – I couldn’t resist a visit on my way back to Chicago. And I got to help a dad pick out resistors for his ten-year old’s first electronic’s project. Neat!
All of the above for less than $20 total. Hamfest, for the win.
I’m particularly excited about the air variable capacitor. After a big of digging around, I pulled this one out of a cardboard box burried underneath a giant box of tubes:
Since I didn’t have either a multimeter or an LCR meter with me, I had to make my best guess as to the voltage rating and capacitance of this unit. When I got it home, it turned out to have a capacitance that varies from about 28pF fully open to 152pF fully closed, with stops at either end. The plate spacing (measured with a caliper) is about 0.060 inches, which means it should start to arc-over at around 2400-2600V.
I have a specific project in mind for this guy: building a small transmitting loop antenna. A range of ~28-150pF should be enough to tune a 10′ circumference loop for the 20m, 17m, 15m, and 12m bands, as well as the 10m and 30m bands with a little fudging (this according to the 66 Pacific Loop Antenna Calculator). With some added capacitance in series or parallel and it could possibly be pushed to 10m, 40m, or 80m bands with reduced efficiency. The air-variable capacitor is key here, since it seems the voltages in a loop antenna can peak over a Kilovolt with just 10-20W of output power! In any case, more thoughts on that antenna as it comes together, but for now I’m drawing ideas from AA5TB, Nonstop Systems, KR1ST, W8JI, and VK3YE’s various projects.
In any case, one of the nice things about this particular air-variable is the reduction drive on it. You can see the worm-gear and larger reduction gear in the picture above – it takes 46 full revolutions of the small stud to shift the capacitor full fully open to fully closed. With a difference of 122pF between the two extremes of the capacitor, that’s an average of 2.7pF per revolution. Even using the bamboo-stick tuning method used by KR1ST (to avoid detuning the antenna by getting close to it), if I can manage rotational accuracy to about 10 degrees of the tuning stud, that’s a resolution of .07pF. Not bad!
One of the things I was on the hunt for this morning was a metal chasis or two to mount projects in. As nice as the Virgin Receiver turned out, I was hoping to find something a little more robust for future projects – maybe some old CD-drive casing or a gutted something or other. There wasn’t a whole lot of that sort of thing around, even in the big-piles-O’-parts, but then this silver beauty caught my eye.
I could see a couple of tubes inside, and from the ‘RCA’ and 1/4-inch jacks on the back (an no jack for a key or mic) I had a pretty good guess it was some kind of receiver, but other that, it seemed like a gamble. When I asked the owner of the table what it was, he very gamely said “I have no clue, but for $2, it’s yours!”
Well, at that price, it’s worth it just for the box! And what I found inside is definitely worth more than two bucks to me:
Judged by the two parts labelled “10.7 MCycle Interstage”, I feel pretty confident that this was indeed a receiver of some kind. More than half of the tube-sockets are empty, so I don’t think it’s worth trying to figure out what they were and bringing this thing back to life.
But check out the nifty components! Up front is a 4.5:1 vernier reduction drive, controlling a two-section air-variable capcitor for some kind of tuning. There’s a 30pF NP0 trimmer cap and a coil mounted directly to the air-variable, which is interesting. There’s a couple of 500K log-scale pots, a bunch of high-voltage capacitors, some old carbon-composition resistors, miniature RF chokes… this thing is going to be a great source of parts, as well as a keen chassis for a future project. Perhaps a regenerative receiver? I could see leaving that classy vernier drive capacitor in place as is and working around it…. hmmm….
This week I had two radio firsts: trying to put together a halfway decent antenna, and a first portable operating session.
I started by putting together a center insulator a dipole antenna. There are manypossible designs online, but I ended up making one with materials I’m familiar with. It’s made of a 1″ PVC cross, four PVC caps, three 1/4″ eye-bolts, some nylon lock-nuts, and panel-mount BNC connector. The whole went together in about half an hour. The PVC connections were surprisingly tight as a press-fit, but they and the eye-bolts are secured with lock-tite and sealed with hot-snot just in case. The BNC connector is soldered internally to a couple pieces of hookup wire, which you can see poking out the sides of the cross. The antenna wires themselves are simply tied to the eye-bolts and wire-nutted to the hookup wire.
The dipole center, a 200′ spool of nylon wire, some “stakes” for securing the antenna to the ground (really, 8″ pegboard hooks, on sale at Menards!), some zip-ties, and a couple of rice-filled socks as counterweight all fit handily into this small plastic case I had lying around:
I live only about a mile from Lake Michigan and the beautiful lakefront park space that runs along the East side of Chicago. I figured with the sunny-but-chilly weather we’ve been having this week, the lakeshore on a weekday afternoon would be pleasant to work in and not too packed with people.
I couldn’t find a suitable table or bench close enough to trees to set up under, but then I spotted the convenient height of the sea-wall between the outer lakefront trail and the lake itself. I couldn’t have been any closer to the lake without getting my socks wet!
I strung up a portable, homemade 40m dipole (wires cut in advance) as high as I could could into one of the nearby trees – I only got the center maybe 20 feet in the air, but that’s still better than the 8′ the random wire in my home office is. The ends are tied off to stakes near the ground. This made the setup more of an inverted-V than a true-dipole.
The antenna is fed from ~60′ of RG-58, running into a ZM-2 Tuner for matching, and then via a short RG-58 jumped into the Virgin Receiver. I also brought along the ardiuno-controlled, Si5351-VFO I’ve been working on to allow for the ability to change frequencies, as detailed in my last post. If I’m going to spend the time setting up practically in a lake, I thought it would be nice to actually scan the whole band. Since the VFO rig is still on a breadboard, I was quite spread-out over my little stony operating station.
So now, the moment of truth – I hooked up the batteries, connected the receiver and VFO, did a quick by-ear tune on the ZM-2. I’ve never done something like this before – would it actually be better than my office random-wire? Was it all just a jaunt in the park? In short, would it work?
LIKE HECK IT WORKED!
Especially up in the SSB portion of the band, there were some stations that might as well have been on the other end of a phone call. (This, by the way, confirms that the Virgin can receive SSB and AM as well as CW.) In no particular order, I heard:
N8KKR, KA9ZXN and others on the Hams for Christ net on 7.263 (330p Central, Monday-Sat). Not my personal bag, but they seemed a very pleasant bunch.
W9DCQ and W4LWW having a nice QSO, between the two of them and some other operators I couldn’t quite copy.
KG9O and KK4FZI having a friendly chat.
Some other snippets of stations.
The listed stations alone include QTHs in Evergreen Park IL, Columbus OH, Middleton WI, Franklin TN, Grassy Creek NC, and Marion IN. None of them terribly far away in radio terms (the Tennessee locations is farthest at ~500 miles), but a great confirmation that the antenna was clear and working. With a height above the ground of less than 1/4 wavelength, the ideal dipole should have a high takeoff angle and be fairly omnidirectional, and that seems plausible based on results.
In sadder news, I seem to have broken some part of the WSPR functionality of my VFO in consolidating that functionality from two separate programs into one. 1W into the antenna and several repetitions netted be exactly zero receptions, either into this antenna or my office random wire. So it’s back into the code I go. While I’m at it, it would really be worth packaging up the little VFO into its own enclosure – having all those wires flapping about is a bit worrisome for transport!
All in all, a tremendously successful, if very chilly, day by the lake. Now that I know what I’m doing, I suspect it would be able to have the station set up and listening in about 10 minutes, and about the same for tear down. With the days getting warmer all the time, I’m sure I’ll be out there again soon.