Dhakajack – Page 43 – A place to put my stuff

Upstairs with NAQCC

We interrupt coverage of Operation Sizzling Pork for this brief mention of last night’s NAQCC sprint, which turned out much better than I would have had any reason to expect. This is a monthly two-hour QRP sprint in which I have participated a half dozen times, usually netting only a few contacts. When I got home from work last night, I remembered the sprint, but was not very optimistic: both main rigs, the antenna tuner, and my keyers are in Indiana, plus a thunderstorm was predicted for prime operating time that evening. However, by the end of the contest, I had made more QSOs than ever before.

an 80m dipole fed through a vinegar jug wrapped in coax — The Belgian Vinegar Antenna (BVA)

With the vintage Collins gear still out for repairs, I had two choices: my 40m rockmite (550 mW) or my ~4W TenTec 1320. The rockmite seemed a bit light for my purposes, so I went with the TenTec. There was one problem, though: the stealth vertical in the backyard is not resonant on 20m, the TenTec’s only band. As of last month, our attic has a newly installed floor, so I strung up a simple dipole from the rafters. I used the former “Belgian Vinegar” antenna, and shorted the radiating wires to sixteen feet, seven inches (calculated for resonance on 14.060). The BVA was basically a dipole center connector plus a gallon vinegar jug wrapped with coax to make an air-core current choke. I wasn’t worried about RF running down the cable in the current installation, so I uncoiled the coax and discarded the vinegar jug. I had used this antenna for two years in Belgium, and during one contest when I operated from Mount Vernon, NY.

temporary station in the bedroom — Temporary Upstairs Station

I didn’t attempt to run coax down to the basement, but just down through the trap door and into the bed room, where I borrowed my wife’s computer desk. Her iMac was temporarily pushed to the side to make room for the station. I did not have an antenna analyzer or VNA, but I did have a power meter that measured forward/reverse power, so in the fifteen minutes before the event, I trimmed the antenna old school, calculating the vSWR. I got it down to about 1.8:1, and figured that was good enough. I was sweaty and itchy from fiberglass and didn’t want to mess anything up right before the contest, so I left well enough alone. With a 25 foot cable, I figured there wasn’t enough power loss to worry about, even at QRP.

Out the window, I could see lightning flashes, and under ordinary conditions, I would not have used the outdoor vertical. However, given that the dipole is indoors and lower than the various metal projections on my roof, I figured I was okay working through the storm. Loud static crashes interrupted work all evening. After each crash, the radio’s AGC would kick in and I’d be deaf for a couple of seconds as sensitivity recovered. Despite the QRN, reception was fantastic on 20m.

I worked eastern and central North American stations in the first half of the contest, as with the vertical antenna, Minnesota and Texas came in particularly well. Around 01:20Z, propagation went long, favoring western stations, particularly Oregon. I was pleased to work NAQCC members in both Canada (Saskatchewan) and Cuba during the contest.

In all, I had 17 QSOs, although I noted that the last one was a repeat, probably trying to be sure that I had copied him correctly on the earlier exchange, so I can say that I have 16 QSOs that count towards a score. All of my contacts were with members, so 2 points each, and made using a straight telegraph key, so a 2x multiplier. I think I did pretty well this week both in absolute score and likely in relative score since I presume that some of the heavy hitters were on the road to attend the Dayton Hamvention.

I was impressed by the performance of the attic dipole, which was refreshingly free of man made noise, versus my usual operation on the lower bands with the vertical antenna. Over the summer, I am hoping to refine the attic installation and make it permanent, routing the wires down to the station in the basement.

Operation Sizzling Pork: Analysis

We went into Operation Sizzling Pork with the intention of having a good time (as we did, see Ben’s photos), rather than as an all out contest. This was something of a shake down cruise with a lot of firsts — it was the first time Ben had worked a contest larger than a sprint, the first time Tymme had operated on HF, and the first time we had tried to pull together this sort of outing. We had some modest, if arbitrary goals, which we came up with the night before the contest while feasting on pork ribs at Squealers Barbeque Restaurant. We decided that if we made 100 voice and 100 cw contacts we would be happy. As our log showed, we hit those numbers and then some:

Band     Mode      QSOs        Pts        Sec
 3.5     CW        71          142        14
 3.5     LSB       21           21         5
 7       CW        61          122        26
 7       LSB       54           54        33
 14      CW        37           74        21
 14      USB       38           38        12
 21      CW        14           28         1
 21      USB       10           10         2
Total  Both       306          489       114
Score: 55,746

So, everything above our goal was gravy, but it’s still worth a little post-event analysis since next time we might want to enter on a more competitive footing.

What worked well:

Logistics. We actually managed to get both materials and personnel to the right location, with some time to spare. Flights, rental car, UPS ground transport. Antennas went up the day before, and the stations went on the air as soon as the contest started. Not bad for a first time effort.
Tymme’s patent-pending arborist slingshot. Antennas (green) went up more than sixty feet, and almost always on the first try. As expected, our actual station (numbered positions) and antenna deployment did not match up with our planned layout (detailed in an earlier post). We had anticipated station a station near the north east corner of the house, but those windows do not open, and the power lines (red) come in on that corner, so we shuffled around. As much as the aerial photos helped with antenna planning, actually seeing where the trees were was another story. We put the NVIS buddipole in the front yard (north, elevated 3~5m), and oriented the low Alpha-Delta DX-EE (elevated ~8m) at right angles to it, between Tymme’s house and garage. The two G5RVs were hung at ~15 and ~20 meters up, also at right angles to each other.
What we actually did
Multiple mode operations. Every station operated in both voice and cw mode. Most of the time, we had at least two radios going, one in voice and one in cw. Sometimes, we managed all three radios. Some RF did get into the Icom 7200, but for the most part, radios did not interfere with each other.
Logging. A secret objective of mine was to convince Ben that the N1MM logging program was not just an ugly holdover from the DOS age, but a finely honed contesting tool. Even I was surprised, however, when we got it to work on a thrown together network consisting of Macs and PCs.
Longer range contacts. We did not do poorly in terms of medium to long range contacts, with 39 states worked in 12 hours. The close in states were worked on 40, and we got out a bit further in the late evening on 80, but the workhorse in terms of medium and long range was 20m.
Weather. We can’t take much credit for this — we were surrounded by thunderstorms, but they went wide of our operating position. We could hear them, but we didn’t have to suspend operations.

Where we came up short:

We did not take full advantage of being a multi-multi, although some of this reflects conscious choices, like not using an amplifier. Since multi-multis are permitted to use spotting assistance, we could have made more use of county spotting sites, dx clusters, etc. If we had more people, putting someone on a spotting radio and/or internet duty could be helpful.
Indiana Counties. There was no particular pattern to counties worked or not, but numerically, we could have done better in terms of counties. One strategy would be to try to track the mobile rigs more effectively, the other would be to try to maintain consistent calling frequencies on each band for people hunting for our county.
Longer range. We had the 40m NVIS going almost all the time, and I think that ate into our use of the G5RVs for 40m operation. We probably could have picked up additional states and possibly counties by using the more elevated antenna for 40m.
The Ring Of Deafness. I’m not sure if this is real or not, but if you look at where were did not work, it seems that there is a skip zone about 1000 km around our location. While I can imagine that the Dakotas are not well represented because nobody is there, this surely is not true of New York. Some of the New England QSO Party might have been swallowed up in this skip zone. What could we do about it? The only solution would be to change the take off angle of our antennas. Maybe it would make sense to have a vertical antenna in the mix to try to complement the coverage pattern of our high and low dipoles.

Considerations for next time:

More bodies. With four operators, we had reasonable coverage, although there were times that we all took a break together, leaving the radios uncovered. With more people, we could operate in shifts, or double-staff each radio, with one person on the radio controls, and on the computer. Having a “spare” person to run around and fix things would also be nice.
The least effective of our antennas was the Alpha-Delta DX-EE, which was intentionally installed low to get some NVIS effect on 40m. When we had started the event, both G5RVs were on a single switch, allowing operating position three to “rotate the beam” ninety degrees. In practice, this didn’t seem like much of an advantage for most calls, and after more than half the contest had gone by, we switched the second G5RV to operating position number one. This opened up some options for that position, and it probably would have been better to have moved it over earlier.
A Voice keyer would be nice. Also, next year I’d suggest programming all of the keyers with the same settings: 1) “CQ INQP NN9S TEST”; 2) “CQ CQ INQP DE NN9S NN9S K”; 3) “599 MONR”.
Better integration with the 7th Area and NE QSOP, maybe the ability to break each contact out of the log for individual submission. It would mean that we would have to copy their full county information as well. This seemed like a unnecessary level of complexity to add this year, but it wouldn’t take much more effort.

Operation Sizzling Pork: The Log

There will be more more posts on Operation Sizzling Pork, but I intend to draw it out. Later in the week: the travelogue, a how-to guide for using Macs during mutlirig contests, and some strategic analysis. Right now, however, my priority is to share the results of the contest with other teams members. I am still doing some sanity checking on the logs and making sure that no contacts were missed due to database synchronization issues, but I expect that the logs I have in hand are 99% final.

This was a 12 hour contest, from 16:00 UTC on Saturday, May 5 to 04:00 UTC on Sunday, May 6. We operated three radios, as planned using four antennas to obtain dx and local coverage. We operated under Ben’s call sign, NN9S from the Chaos Lodge in Bloomington, so our exchange was “MONR” for Monroe County, Indiana. All stations ran N1MM in a networked configuration, with the database replicated across all machines.

We logged 314 contacts, but 8 were duplicates, so 306 usable contacts. In some cases, we were able to log two entries when contacting mobile stations parked on county line boundaries.

Of the 314 contacts, 128 were phone and 186 were cw (morse code). Station 1, an icom 7200 at 100W to an Alpha-Delta DX-EE at 25 feet logged 83 contacts. Station 2, a Kenwood B2000 at 100W to two orthogonal G5RVs at 40 and 60 feet, respectively, logged 148 contacts, and station 3, a Kenwood TS-450 at 100W to a buddipole configured for 40m NVIS operation logged 83 contacts.

As predicted, 40m was the workhorse band and remained active throughout the entire event, yielding 119 contacts. 15m was strong earlier in the day, and produced 24 contacts across the country, drawing strongly on participants in the 7th Area QP event. We also had a phone and cw contact to Venezuelan stations on 15m. In the late afternoon, 20m was helpful for both national and international contacts. Tymme had a run of six Italian stations on phone from the ARI contest. The 15m band dropped off around 6 pm local time, but 20m continued into the late evening. Around this time, the New England QSO party was also in full swing, providing contacts on 20m and 40m. Around 9 pm local (01:00 UTC), we started working 80m and continued until the end of the contest, working a total of 93 contacts.

At several points during the contest, we were spotted on various clusters resulting in bursts of pileup activity. Here’s a search from DX-cluster performed earlier today:

During the contest, we did well in terms of long-range multipliers, having worked 39 states and 5 provinces. Our U.S. states included AL, AZ, AR, CA, CO, CT, DE, FL, GA, IA, ID, IL, IN, KS, KY, MA, MD, ME, MI, MN, MO, MT, NC, NH, NJ, NM, NV, OH, OR, PA, RI, TN, TX, UT, VA, VT, WA, WI, WV, and WY. The provinces included NS, QC, ON, MB and BC. We worked WB8WKQ in MI, WA3HAE in PA, and W7RN in NV four times each on various bands and both modes.

Our coverage of Indiana was more spotty, particularly in the southeast corner. Overall, we reached 35 out of 92 counties. It looks like the NVIS signal and the low multiband antenna performed well. Within Indiana, KV9X yielded four log entries, but was really two contacts spanning county lines. We worked a number of other stations three times including N9FN, N9LF, and W9LJ. Our single home county contact (MONR) was with the Indiana University station, K9IU.

Our final score will end up being something in the neighborhood of 55,000 points, which is pretty decent considering that this was a first time effort and that we are not experienced contesters.

Operation Sizzling Pork

Several months ago, I bounced an idea off Ben (NN9S) and Tymme (K9TYM) — why not get together for some sort of radio operating event? I reviewed the contest calendar and suggested the Indiana QSO Party, a laid back twelve hour contest on May 7th. Tymme has a technician license, but has not had much chance to play with HF, while Ben recently got this extra ticket, but has not taken part in many contests. Not that I have much more experience, but I have been around other people who do know what they are doing in contests, and hopefully, I’ve learned from them.

So, for the last few months, we have been scheming and setting in motion all the logistics to make this event happen. As a first step, we agreed to operate from Tymme’s house near Bloomington, Indiana. There is a lot of land around the house and some tall trees (although, not as many as last week, prior to the storm that sent one through the roof of Tymme’s cottage). We took stock of our equipment and decided that we could probably put three rigs on the air at once, maybe more if we had more participants.

So, here is the plan (after next week, we can see how close we came, and where Murphy sent us in a different direction): Some equipment for this event was ordered and shipped directly to Tymme’s, things like the G5RV antennas, switch boxes, and extra coax. Conveniently, we justified the cost of these items by thinking that we’ll use them again. I’ve also shipped my main station to Tymme’s in a few boxes via UPS. It’s cheaper than flying them out as luggage, and probably safer as well. I will fly out to Chicago on the evening of Thursday, May 5th, pick up a rental car, and catch some Z’s at a hotel near O’Hare. The next morning, I’ll be up early, drive to Ben’s and load the car with his goodies. If anyone else from Chicago wants to come, we can pile them into the car, and/or tie them to the roof, trunk or fenders. Then, it’s a classic road trip down to Bloomington. On the way, we cross back over the time zone, ending up on Eastern Time.

Friday will be set up day, the big items being hanging the antennas, running the feedlines, setting up the workstations and installing the logging software (N1MM) at each workstation. The workstations also need to be networked together to share data in realtime during the contest. Later in the day, we should have some time to review the rules and strategy for the contest and to test the equipment on the air.

Saturday is the day of not only the Indiana QSO party, but several others including the 7th area call party, the New England QSO Party, the SKCC sprint, and the Italian Amateur Radio (ARI) contest. The Indiana event doesn’t kick off until noon, so we can work on our contest style for a bit using one of our personal call signs to make contacts.

At noon, we’ll go on the air with up to three transmitters at once. Although everything is subject to change, we think the configuration will be as follows. Position 1: Kenwood B2000 at 100W to orthogonally oriented G5RV antennas via an LDG 100 Pro II tuner. 2: Kenwood TS450 at 100W to a low horizontal buddy pole configured as a 40M NVIS antenna, possibly switching to a higher 40/20 dipole; this position will use the TS-450’s internal tuner. 3: Icom 7200 at 100W to a high Alpha-Delta DX-EE 40/20/15/10 multiband dipole, possibly switching with an orthogonally oriented dipole via an LDG Z100 tuner; 4: Yaesu 817 QRP spotting radio, to a 40/20/10 end-fedz antenna.

We are hoping to operate the entire twelve hours of the contest. With strategy and logistics largely addressed, we are now turning to more important matters such as what will eat during the event? Mother Bear’s Pizza sounds likely on Friday night and a trip to the Runcible Spoon for breakfast on Sunday. During the event, we are considering putting on a pot of soup plus finger foods.

Digital Restoration Day

I hereby declare Thursday, April 21st was Digital Restoration Day. The moment I walked in the door after work, Lara pounced on me and told me that she had shut down her computer because a window had popped up indicating that she had fifty or so horrible viruses on it. As she guessed, it was a fake message produced by adware of some sort. Starting with the usual, I ran microsoft security essentials, which identified and quarantined the adware. I did a manual update of the malicious software removal tool and gave that a run as well. After a reboot, the machine ran normally, and Lara went back to her online projects.

My next project was my cell phone. I live on my android phone, but it had been getting quirky for the last few months — long latency when switching apps, unexplained crashes, general orneriness. Last year, I had gotten tired of waiting for T-mobile to upgrade my HTC Magic 32b (i.e., T-mobile MyTouch) from it’s original (v 1.5?) android install. Mainly, I wanted tethering ability and some of the bells and whistles of the later versions. T-mobile kept promising over the air upgrades, but after a few months, that got old — particularly when all of their new and shiny phones were being sold with the new operating system, but I was stuck with my dinosaur.

Last year, I rooted the phone and installed a then-current version of the Cyanogen Mod. The HTC Magic followed the Google G1, so it was the second android phone on the market. Although it supports a 8 GB sdcard, the onboard memory is limited, so I had to install the “tiny” version of the Google apps, and otherwise be careful about memory allocation. Over time, the phone slowed down and became buggy. It got quite annoying. Tonight, I grabbed the highest version 6 cyanogen stable release, did a factory wipe/reset, and installed the updated operating system. It booted without a problem, grabbed my settings from the cloud, and I’m back in business today with a phone that is not only more stable, but a lot perkier.

Now to reload some apps.

Next Year Jerusalem; this year Hungary

I had another go at the rockmite last night on 40 meters. I tuned the LDG tuner to 7.028 with the Kenwood B2000 and then substituted the rockmite for input; antenna was the 43 foot tree-slung vertical wire. The LDG has latching relays, so it stayed tuned even when the drive was removed. I started calling around 18:30 EDT (22:30 Z) and was answered by W2XB, Don in Lakeview, New York (a bit south of Hamburg, along the shore of Lake Erie). Don was using an Elecraft K3 and gave me a 349. His signal was weak but copiable (after I asked him to QRS down to around 15 wpm), so I gave him a 359. The rockmite is not very selective and there were signals up and down probably a khz, so most of the filtering was done between yours truly’s ears. This contact went back and forth three times, and I can’t say that I copied every last letter, but the signal was quite stable. So, that is QSO number 3 for the rockmite, 282 miles (~450 km) on 550 mW.

After listening to the rockmite for a while more, my head was beginning to swim. I craved the narrow filtering… no, make that any filtering whatsoever, so I fired up the Kenwood and sent a QRL on 40m. I was answered immediately by a “?”, so I cq’d, and was surprised when HA3OD, Arpi, came back to me. I believe he said that he was operating at 30W from a location near Pecs, Hungary. So, about 4600 mi (7400 km) on 5W — even better than the rockmite.

I’m pretty happy with QRP performance last night. Propagation conditions were not particularly great (prediction for the band was “fair”), but noise was less of a problem than usual. I am considering building some sort of audio filter to narrow the rockmite experience. I know that there was a rockmite filter, but I don’t believe it is still available. I’ll have to look around a bit.

Rocky Road

Yesterday, my brain was mush, so I didn’t attempt anything at the workbench. I turned on the radio and tuned around the ten meter band, not expecting to hear much. However, I did hear considerable activity from South America, calling with “MM TEST”, which turned out to be the Manchester Mineira contest. Since the contest originated in Brazil, it wasn’t surprising to hear so many stations from that country. I had my first contacts with Peru and Ecuador, and logged a few with Columbia, Aruba, Cuba, Mexico and a few U.S. stations. I heard Chile and Panama, but didn’t manage to land them. I only caught the last couple hours of the contest and did not try running at any point.

Afterwards, I plugged in the 550 mW rockmite 40 and tried calling for a bit. The signal went through my LDG tuner and then my 43 foot vertical wire in the backyard. The band conditions were not great last night, but the activity level was relatively high. I tried for about an hour, and stopped around midnight. I figured that I might have more luck the next morning, with fewer competing signals (but also fewer listeners awake). I started calling around 6:30 and went about 45 minutes. Local sunrise was 06:27 EDT / 10:27 Z, so 40m was fading towards the end of that period. I didn’t get any responses, but I was picked up at reasonable levels on the reverse beacon network, by stations from Massachusetts and Georgia.

At one point this morning, my ears were nearly blasted off by a New York station operating on 7.031-something. I cranked the RF gain all the way down on the RM40, but it was still loud. The reverse beacon network registered the station at 51 dB above background in Illinois and Maryland — that’s about 10,000 times stronger than my 500mW signal, so I have to guess that the station was using either a linear amplifier or had one heck of an antenna. Even operating more than 3 khz away, he cooked me.

So, no cigar so far on the higher-power RM, but I am sure that the signal is getting out. Maybe I need to keep an eye on the QRPspot site.

Honey, I blew up the amplifier

Actually, let’s start on a bright note, and then we’ll get to the part involving smoke.

Inside view of the rockmite 40 installed in a mity box — The Rockmite 40

My main reason to build the amplifier was to get a bit more power out of the rockmite. Part of the problem in getting the amp working was also likely low driving power. The basic design of the rockmite uses the prototypical bipolar NPN for the “final” amplification — a 2N2222. There are variants that use other transistors and get the power above a watt, and there are also some tricks to increase the drive, but the stock rockmite should yield a nominal half watt or so with no mods. So, I took off the cover of the rockmite and poked around, checking all the part values. I had already made one substitution: C8 was decreased in value from 0.1 uF to 0.01 uF to knock the side tone volume level down to something tolerable.

Sure enough, I saw the problem — I had used 47 pF (marked 47J) instead of 470 pF (marked 471) for C15 and C17, which are on the output side. Yes, the “1” and the “J” looked similar. I stuck the right value capacitors in, and power output using a 13.2V supply was 550 m. Not too bad.

Next, I plugged the RM into the Texas Topper. I didn’t power it right away, though, because I was interested to see what sort of insertional loss the Texas Topper introduced when it was not active. Power output was about 400 mW. This probably wasn’t an entirely fair test because the Tx Topper was still on the bench top, with tack-soldered connections to the BNC connectors.

Texas Topper Partially Installed — Texas Topper before final install

I removed the extra N4148 from the amplifier, because I figured it probably had enough drive now to work without extra bias. Power output was measured as 2.2W, so about 6dB gain. While I could live with that (and, in retrospect should have), I was curious what would happen if I bumped the bias back up a bit. The N4148 went back in, raising the bias voltage from about 2.05 to 2.75V. Power output was now 7.7W — 11dB gain. I measured roughly 7Vpp in, 20Vpp out, so roughly in agreement. Part of the increase in gain might also have been due to switching from using alligator clips to apply power to using a thicker wire terminated on one end with a power pole connector and on the other end with a type N coaxial plug.

So, at this point, I was actually (hah) thinking of introducing a one or two dB attenuation pad, although the idea of burning off power in a QRP rig feels inelegant. More inelegant, however, was trying to bend the FET forward so the heat sink would fit in the enclosure. When I pushed it forward (yes, with power applied), there was a bit of sizzle and then a bright flash from the LED. I don’t know if something arced before the LED toasted, but I was left with the acrid and no doubt carcinogenic aftertaste of stupidity wafting through the shack.

I inspected the board around the FET and couldn’t see an obvious short. The parts in that area do share some close quarters, and the heat sink is right next to both transformer coils. I took out the LED (shorted now) and yanked the FET. Good thing I had a bag of them on hand….as will soon be even more evident.

With a new FET, a new LED (not quite the same type, but close), and another diode, I was back in business. Everything was fine until I tried to stuff the heat sink into the enclosure. This time, not under power. The problem is, though, at some point, you have to apply power, or the whole thing is just a paperweight. Zot. Sizzle. Flash. Puff.

Yeah. So, at this point, I’m out of FETs and thinking that maybe I need to do something more creative regarding the strained relations between the heat sink and the enclosure. The heat sink should be applied right to the metal tab on the FET, which is the drain. The case is aluminum, and at ground potential, so that particular twain shouldn’t meet.

I tend to only order from Mouser when I get enough items on my “want” list to make the shipping work out, so it might be a bit before I replace the burnt out components, but I’m sure I will in the next couple weeks. The board has held up very well to my repeated soldering/unsoldering, and I really don’t have any complaints about the Texas Topper per se. This is more a mechanical issue at this point — all the electronic bits seem to do a fine job of amplifying. I may, in fact, order another one just to play on another band.

Even without the Texas Topper, doubling the output of the Rockmite should make it more usable. I’m looking forward to rolling both it and the TenTec 1320 out next week for the QRP to the Field Event.

Texas Topper QRP Amplifier

I seem to be doing well enough running the Kenwood B2000 at 5W or the TenTec 1320 at around 4 watts, but I haven’t made many contacts with my Rockmite, which on a good day puts out around 250+ mW, but less when the battery runs down a bit. A while back, I had ordered the Texas Topper (a.k.a. Tuna Topper) amplifier (nominally 5W out) from www.QRPme.com. For $25 it’s a good deal. The design lends itself to flexibility and experimentation, allowing the user to choose whether to use onboard/offboard options, a tuna-shaped round or altoids-shaped rectangular form factor, a range of input powers (using fixed or variable attenuator, if necessary), fast/slow switching, and transceiver or xmtr/rcvr configuration.

I put the kit together last week, made an enclosure, stuck it in, connected everything up, and … nothing. Well, not quite nothing. My WM-2 wattmeter read about 50mW output. Not good — the amplifier was doing something, but not in the direction that I had hoped.

The amplifier is well-documented on Chuck Carpenter’s website, which provides a parts list, pictures of the board, schematics and helpful advice. From the circuit diagram, it’s apparent that there are two halves to the pc board — one that controls switching through a relay, and the business end of the amplifier that centers on a MOSFET followed by a filter network. As far as I could tell, nothing was shorted. In the “receive” state, signals fed straight through from input to output connectors. When I keyed down the rockmite, I could hear the relay click in, and I was able to verify that the input signal was being appropriately routed over to a 4:1 transformer to feed to the MOSFET.

I checked DC voltages with a DVM, and verified that the bias voltage (determined by the forward voltage drop across an LED that conveniently also serves to let you know power is applied) was 2.05V. The voltage on the MOSFET’s metal tab (the drain) was about the same as battery voltage, as it should be. Unfortunately, I didn’t have an RF probe on hand for tracing of RF voltages — the probe was lost in the last move. It would be easy enough to build one (see nice plans on W5ESE‘s site), but I didn’t have a suitable diode on hand and apparently Radio Shack no longer carries the 1N34 in stock. No problem — I have something better, although not quite as portable: an oscilloscope.

The incoming signal was about 8Vpp, and 4Vpp after the 4:1 input transformer. I expected to detect something on the drain of the MOSFET, but all I got was hum (maybe just background). Probing beyond the MOSFET, I didn’t get much. I was stumped at this point, and starting wondering if I had done something wrong during construction.

It seemed to me that there were two likely places that I could have screwed up — in winding the two bifilar transformers (which, I recall I did while watching an episode of “No Ordinary Family”, so maybe I was distracted), or maybe in installing the MOSFET. I had placed a mouser order at the same time as the kit order, so I had a couple extra MOSFETs to play with. Using static-free everything (mat, wrist band, soldering tip, etc) and low heat, I replaced the MOSFET. No change. The kit comes with 22 and 26 gauge red magnet wire for winding toroids. To be extra careful, when I rewound the two bifilar transformers, I used on strand of red, and a strand of another color. Radio Shack does carry a magnet wire set, which conveniently includes 22, 26 and 30 Ga lacquered wire, and the 22 is gold and the 26 is green. The transformers look much better when wound with two color wire, and it’s easy to verify at a glance that the correct wires are tied together and that they all end up where they should. Again, though, no change.

I tried replacing the MOSFET one more time, as I thought that perhaps I had not had the right load on the amplifier when I tested it the first time, but again, no change.

After I looked at the data sheet for the FET and noted that the gate threshold voltage is listed as a minimum of 2v and max of 4v. The transfer function graph showed the drain current picking up sharply above 4v. My rockmite has lower output than most, and it occurred to me that I might be at the lower end of this amplifier’s design — not enough umph to drive the FET’s gate. To up the bias voltage, I stuck a 1N4148 diode between the stock LED and ground. This bumped the bias from about 2V up to 2.75V. Result: 1.5W output. On the oscilloscope, the waveform was a bit distorted on the FET’s drain, but smoothed out in the filter and was well formed at output. Going from 250 mW to 1.5W is somewhere around 7dB gain — not quite the 10 dB gain typical for this amp, but a huge improvement over my rockmite’s usual output.

So, now I am playing around a little to see what happens when I run this system with a fully charged battery and play a bit with the bias voltage. Hopefully, I’ll have a chance to try out the rockmite-on-steroids this weekend.

No QSOs in Boca Raton

This started as more of an IF (interactive fiction — not intermediate frequency) blog, but it does make a lot of sense to consolidate other topics here as well, since most of the time when I have to list a “blog” or “web site” link, I list this one. So, consider the flood gates opened. That probably means a flurry of excited posts followed by intermittent (on a geological time scale) dry spells. Let’s face it: that’s just how I am about updating websites. Maybe postings will be more regular if I can broaden the scope of the posts to just about everything and if the blog posts are useful to me as a sort of lab notebook.

Along these lines, one topic I’d like to document is ham radio trips, which I will conveniently define as any time I am not at home and get to play radio. Since I take a lot of trips for work, and since I almost always take a radio along, there should be a bunch of these. Very often, the conditions aren’t optimal, and I don’t have a lot of time on trips, so more often that not, I probably won’t make that many contacts, but it’s more the effort than the QSO count.

Rather than recount projects and outings to date, I’ll just start from here forward. This weekend, I spent a couple days in Boca Raton. Scratch that. That’s how it is listed on the map — it is actually Deerfield Beach, Florida. It’s only a beach if you consider concrete to be beach-like. It’s inland a few miles, and the view was of route 95. The conference I was attending was held at a resort that actually *is* in Boca Raton and overlooks the the ocean, but I’m travelling at government rate, and that only goes so far.

My room was on the third floor of the hotel, right near the front entrance, which made antenna placement challenging. On the first evening, I bid my time until there were no cabs or cars in the oval driveway, and then lobbed a 65′ long wire over a palm tree. I had attached it to a water bottle, and A long wire antenna running from the window to a palm tree couldn’t see where it landed after I gave it a toss. There were a couple tense moments when I went looking for it outside and found it dangling 20′ above the driveway, over the heads of some oblivious guests. I managed to yank it back a bit and get it into the bushes. Later that night, after dark, I guyed it down more substantially. Most of the antennas was elevated at about 35′, with the distant end down lower. I ran a 35′ counterpoise around the room and tuned the whole thing with a Hendricks SLT+ tuner.

The rig du jour was the 40m Rockmite, with the 7028.0/7028.9 crystal, running from a 7.2 Ah absorbed glass fiber lead acid battery. A picokeyer was built into the rockmite, and morse code was generated by a Palm Paddle which was duct taped to the battery. Where the wire crossed the metal window frame, I wrapped some duct tape around the wire as padding and then closed the window snuggly. Luckily, the hotel cleaning crew didn’t mind wires sticking out the window, and left the whole thing intact while I was attending my meeting on Saturday.

So far, I have had two — count them, two — contacts on the rockmite, but considering that it only puts out 300mW, that’s not too bad. Both have been from home using my 43′ vertical antenna (which is nothing more than a vertical wire radiator slung into a tree plus a few ground radials). One contact was across town, the other was to Michigan. In the Michigan case, I was responding to a CQ call, and it was a difficult QSO.

I had no problem hearing other stations calling on 7.028 plus or minus 1 khz. Powerful stations would cut across both of my frequencies, and I had to wait them out. I heard strong signals from Italy, Slovakia, Slovenia, Germany, Croatia, France, and around sunset, from Columbia. Some strong local signals (SC, GA) were zero beat, but I could not work them. I called for a few hours intermittently, but had no responses. Well, maybe some qrz’s, but I am not sure to whom they were replying.

This was the first I had tried out the SLT tuner with the rockmite. Interestingly, the rockmite is powerful enough to illuminate the LED that tells you when the system is resonant. I would have wondered if my signal were getting out at all, if I had not had some confirmation from the reverse beacon network. Apparently, I was just above noise for a few of the stations, but at times, my signal was pretty decent (also, though, taking into considerations that the receiving systems for some of these reporting stations have high gain antennas).

So, no bites, not even nibbles, but considering that the antenna was somewhat of a compromise, I’m not writing off the rockmite. I am, however, strongly considering finishing the Texas Topper amplifier, which would boost the signal nearer to 5W and give me a fighting chance when my antenna options are limited.