3S4 QRP Midget

Last week I paid a visit to my friend Skip, K7YOO, in Winona. While rooting around in his parts storage I noticed a little transmitter. I've a weakness for QRP homebrew and this one, with miniature tubes, is of an era I don't have covered. A couple of days ago Skip dropped it off here in Rochester as he headed for the airport.

It is a version of the "QRP Midget" first described in July 1967 Popular Electronics by W5LET. Dave Ingram also covered it in November 1992 CQ. This one is build in a little bigger box with an added current meter and RF choke in the B+ line but otherwise it is a good copy of the original.

This transmitter uses tubes designed for battery powered portable radios common just before transistors took over the market. Two "power" pentodes in parallel run about a watt out on 80 or 40...not a barn burner but it should be good for some contacts.

Now I need to come up with a receiver along the same lines...

Spring at Last!

Spring is here at last, but I did have to drive 150 miles to find it.

Some extra time in my travel schedule today gave me the chance to do my first Picnic Table QRPxpedition of 2011. The I90 rest area just outside of Mauston, WI turned out to be fine place to stop, have some lunch, throw the antenna up into a tree and see who I could work. Mark, KQ0A, in Taos, NM heard my "QRL?" on 14.060MHz and gave me a call. He was 599+ the entire QSO while he gave me a 579 with some QSB.

With the solar cycle heading up I'm planning a lot more great QRP QSOs this summer.

More TZ-20 Amplifier

My TZ-20 Amplifier project has been on hold waiting for some sort of rack to mount it above my 1934 transmitter. I finally got some help from Skip, K7YOO, to cut and bend a piece of 16 gauge aluminum to form the shelf. 1" angle aluminum is used for the vertical legs and the shelf supports.

Once warm weather returns to Minnesota I'll take the rack apart and give it a few coats of paint, probably black wrinkle to match the rest of the station.

Winter 2011 CX

Yesterday was the Winter 2011 Classic Exchange. This event offers a great chance to get on the air with older gear. Participants putting multiple vintage transmitters and receivers on the air have a big score advantage, but it's fine to put only one vintage station on the air or work others using, even, a software defined Flex-5000A.

This year, after going through the possibilities, I settled on five stations I'd like to have in the CX:

• Drake R4B/T4XB
• Collins 75A3 / EF Johnson Navigator
• NC270 / Eico 720
• NC303. EF Johnson Ranger II
• NC101X / 1934 "46 Job"

In all I made 11 contacts (but only 10 counted for points) and I used 4 of my 5 stations. The CX gave me a chance to play with a couple of radios I haven't used in a while and to fine tune a little what I'm looking for in my favorite "boat anchor" station.

2010 AWA Bruce Kelley QSO Party

The last two weekends I participated in the AWA Bruce Kelley QSO. Except for curious visitors, transmitters must be limited to 1929 (or earlier) designs and not crystal controlled.

This year I used my Hull Hartley at 10 watts input and a Drake 2B receiver. The change from last year was having a 80 mtr vertical available rather than a simple end fed wire. Unfortunately SE MN was under a blizzard warning for most of the first weekend of the party and I was busy elsewhere for most of the second weekend. Self excited oscillators like the Hull Hartley are prone to frequency wobble whenever the antenna load changes. My vertical swaying in the blizzard wind was too much for it. Rather than wobble all over the band I again used my 105' end fed inverted "L".

Even with only 3 watts out to a low (10' -15' off the ground) antenna I made 11 contacts and worked both east and west coasts. I had a good time.

Maybe next year I'll have an amplifier for my Hartley so that I can use the vertical (with the sway) and run closer to 6-7 watts out.

80 Mtr Vertical Performance

I wondered if my 80 mtr top loaded vertical is a good antenna for the Bruce Kelley Memorial 1929 CW QSO Party. Part of the loading is the top 6' of two of the guys. Any sway at all causes a guy to sag a little shifting the load my Hartley sees. This causes my signal to FM/wobble...distracting to say to least and aggravating if the band is crowded. I needed to know if the gain offered by the vertical over my endfed wire was enough to outweigh the the wobble it introduced.

The reverse beacon network at http://www.reversebeacon.net/ allowed me to get a good idea of real antenna performance. All I had to do is call CQ and any reverse beacon stations hearing me automatically posts my call, frequency and signal strength to the web. By switching between my low endfed wire and my vertical I could get a good A vs B comparison. By doing this over a period of time I could see how changing nighttime propagation impacts this comparison. Monday night I did exactly this and then sorted though the data to see how the two antennas compare from about 8PM (2:00 UTC) through the next morning.

What I found was that for the east coast (PA) the vertical offered 8-10 dB gain throughout the night. While not always a spectacular performer it is almost always better than my endfed wire...but signal reports all mention the wobble/FMing introduced by antenna sway. Based on this I'll stick with my endfed wire for the early evening hours and then switch after about 10PM when the band activity dies down a little.

For next year's Bruce Kelley QSO Party it would be nice to have this problem solved by building a '29 style amplifier to use with my Hartley. Fortunately my 1934 transmitter already has an amplifier stage in between the oscillator and the antenna. My vertical will work fine with this transmitter during the AWA Linc Cundall Memorial CW Contest in January.

More 80 Meter Vertical

Yesterday I did the final pruning on my 80/40 meter vertical.

This antenna is a big improvement over my 105' endfed wire. Last night on 80 CW running only about 10 watts I worked KK1K (VT), VE7SL (BC) and VE3AWA (ONT). All gave me good signal reports and had no trouble with the QSOs. In addition VE7SL reported I went from s6-s7 to unreadable when switching back to the endfed wire. VE3AWA reported that I went from s9 plus to s8 when switching to the endfed wire.

I also checked my antenna performance used the Reverse Beacon Network at http://www.reversebeacon.net .This is a network of receivers/computers connected to the internet. They auto log the frequency and signal level of any CQs heard. By calling CQ using both the vertical and the endfed wire I got a good idea on how the two antennas compare. The network consistently logged me when I used the vertical and never heard me when I used the endfed wire. At the locations on the Reverse Beacon Network, the vertical was the clear winner. But there were no reverse beacon stations in MN, WI or IA. My endfed wire might have done better if evaluated using nearby reverse beacon stations locations.

I was asked about my radial system. I have eight 30' insulated wire radials stapled in the grass. 30' seems short, I expected to need 67' (1/4 wave on 80) long radials. I measured the resonant frequency of the radial system as I would an 8 element fan dipole with two 4 element halves. 30' seemed to be right. Velocity factor must have a big impact on the length of ground mounted radials.

This new vertical should definitely help my AWA QSO Party scores.

More 80 Meter Vertical

Beth has commented that I need to get a "Frequent Buyer" card for my local big box hardware store. Since starting on this project I've been making trip after trip to buy yet one more bunch of screws, a particular clamp, a spool of wire, a ..... the list goes on. For a project that started with a $7 set of fiberglass poles this one certainly is a great example of "the devil's in the details".

I'm finally to the point of pruning it to frequency. Along the way I've fashioned a hinged base out of a large gate hinge and two conduit hangers, I've added 40 meter capability and I've made the bottom 23' a four wire vertical cage. Top loading is provided by two 6' elements forming the top ends of two of the guys, a coil wound out of 14 gauge insulated wire on a piece of 4" thin wall PVC sewer pile and a vertical 6' element. 40 meter coverage is provided by a 9' stub (connected directly to the top of the 23' vertical cage below the coil) that makes up the top of the third guy. Additional support is provided by tying the mast to my deck railing at approximately the 9' level.

Normally this will be a winter installation. I plan to paint the mast white.

Actual on the air reports will need to wait until I finish tuning it to 3560KHz.

80 meter vertical

As I look forward to cooler weather I've starting to think about 80 meters. With the winter months 80 becomes quieter and a better band for "DX". 80 is also to best band for my 1929 transmitters. I'd like to put up a better 80 meter antenna. Right now my endfed wire is only 10'-15' off the ground. If works OK for Minnesota but not much else beyond that. The radiation angle is too high. My backyard was too recently a corn field. Nothing back there is tall enough to support a higher dipole or end fed wire.

I'm going to start with a 30' to 35' 80 meter center loaded vertical and maybe even top load it a little. For a mast I'm going to try some of the fiberglass camouflage netting support poles / antenna masts seen on ebay these days. AI4WM has a good article on the web describing these poles . I found some with the fiberglass reinforcing ring on ebay fairly cheap. A trip to my local big box hardware store resulted in several "attachments pictured:

1. 1.5" Conduit Hanger - This allows me to attach coils, pulleys, etc to a mast or they can be used to attach to mast to something else (like a fence or a post).
   



2. 1.25" PVC Cross - This fits nicely over the top/male end of the mast.
   
   
   



3. 2" x 1.5" PVC Reducer - This I found in the electrical department. With a little drilling to add a few wire loops I should be able to use this to attach guys
   



4. 1.25" PVC Plug - This goes in the top (when mounted) arm of the PVC cross. It will give me a place to add a 6' whip above the top fiberglass mast.
   

More C-Pole Vertical Array

After building/using my two C-Pole array I'm starting to rethink my plan.

KF2YN's C-Pole vertical array design calls for dedicated C-Poles (each pruned to have a 25 ohm input impedance) and phasing lines that both transform the antenna impedance to 100 ohms and set the phase delay between the two antennas. On the surface this looks doable but I've a lot of concern about getting the phasing lines right. W8WWV's measurements showed about a 4% delta as he measured the electrical length of a 17.1' long piece of coax. Also, I don't want to dedicate two C-Poles to an antenna that I won't be using much.

A local friend of mine wants to build a self supporting C-Pole antenna like mine. I can feed two verticals with arbitrary (but equal) lengths of coax and a simple Tee connector at the antenna tuner to make up for the 25 ohm combined feed impedance...no need to worry about electrical lengths. In addition, self supporting antennas can be positioned anywhere to point my signal where I want it to go that day. I can even boost the gain a little (up to 4.8 dB) by separating the antennas 5/8 wavelength.

It's still August, I should have another couple of months of outside weather here in Minnesota.