Antenna work: new 6/4m beam and setting up a 20m windom antenna

After a trip to OJ0 in 2023, I decided to buy one of the 6/4m yagi antennas used by 1UW during the expedition. My plan was to mount it up by the cabin, using the already existing pole currently being occupied by my 20m vertical antenna. This new antenna in question is the EAntenna 5070-OWA8, a 8-element yagi antenna with the elements evenly divided across the 6 and 4m band. The two bands share the same feedpoint, meaning a duplexer is required if one is to use different transceivers for the two bands.

The new addition to the radio shack.

The antenna is fairly easy to install, only having to screw the elements into the center pole once the correct order has been clarified. This first install was just a proof-of-concept, confirming whether or not 6 and 4m was of any interest at this QTH. The first results were quite disappoiting, not having any luck reaching other operators using FT8. Not having the NanoVNA with me neither, I could not find what frequency it was currently tuned for. For now, the antenna was at least mounted up and hopefully only minor adjustments were required to make it operable.

During my recent visit, I found that I had put the feed cable across the center pole, and not straight down like pictured in other installs online. As this is fairly plug-and-play antenna, I immediately thought for that to cause some disruption to the antenna.

The first attempt at installing the EAntenna-yagi, with the wire going over and under the center rod, and the cable coiled up quite a lot of turns!

Another quite obvious culprit was the tuning of the driven elements for 6 and 4m, which has a innter tube allowing for a limted adjustments. As this antenna was used quite close to a metallic roof last time, the move to its new QTH could definitely call for some adjustments. After moving the cabling and tinkering with the adjustable elements, the antenna showed a much more promising SWR measurement, with the center frequency at approx 50.300Mhz.

Doing mast work alone, the available mast attachment is handy as a parking spot for your equipement. Notice the mosquito repeller right below the rotor.

Next came the time to install the antenna rotor, which I had also previously used at OJ0 with good results. The antenna rotor is quite simple, consiting of a 3-wire controller and the outdoor rotor-unit itself. The rotor is Conrad 284971, though with the same controller also known under the name HyGain AR-303X. As the old mast consisted of two 1.5m mast rods that had been irreversibly put together (by design, of course), I had to find some other rods. Luckily I had a heavy-duty steel rod that I once received from a friend, plus another one of the light-weight 1.5m aluminum rods readily available. The former was placed on the bottom, with the lighter one placed on top of the rotor for the antenna mount.

The indoor rotor control unit in the shack.

The new 6/4m yagi, mounted ontop of the Conrad rotor.

The final installation turned out quite alright, although definitely with room for improvement cable management wise. I’ll let it run for a while and see how much slack is needed for full rotor rotation, and fasten the cables probably once everything seems alright.

With the new 6/4m antenna now in the location where my 20m 5/8 vertical antenna previously resided, I had to find some other means for communicating on the 20m band. Mounting the 20m antenna at ground level seemed a bit dauting as we have pets running around the garden, as well as a lot of vegetation making it a difficult job. Since the cabin is on the slope side of a hilltop, most of the coverage would also be down south. Instead I opted to install yet another dipole antenna, this time trying my luck with a windom antenna.

I already had a 1:4 Fritzel balun available, which seemed like a good alternative to the 1:6 balun used in some other windoms. The first step consisted of fixing the balun, as it was currently falling apart. After applying a healthy amount of glue and waterproof sealant, I think this balun will keep itself in one piece for a while. Luckily the balun itself and the internal connectors looked fine, but tighetning them before sealing the box seemed like a good idea regardless.

With a lot of help from this site, I tried narrowing down my options, especially as the total antenna length for my designated mounting location would be a challenge. I originally thought about building a Fritzel FD3 equivalent, which quickly summarized is a shortened FD4, covering just 40/20 and 10m (with options for covering 15m as well.)

The 1:4 Fritzel Duplex balun ready to use in the windom antenna

Hooking it up with the appropriate lenghts of wire for a FD3 antenna, about 13.8m and 6.9m for the two sides, I found two things: The antenna was obviously too long, and adjusting it would definitely take some me some time. As I already had made the fastening points for the designated space, I decided to go back to the drawing board.

The windom formula is quite simple, only really differing from a dipole antenna in the ratio of wire present on either side of the balun. For a windom antenna one of the sides will be 2/3 of the total lenght of a 1/2 wavelength, while the other side will be 1/3, making up the full 1/2 wavelength in total. With this formula I decided to make a “FD2” antenna, just making 20m the lowest band and making the adjustments accordingly. In summary, this means the legs of the windom would be half the length of the FD3, which in turn is half the length of that of the FD4 windom antenna. Great!

The 20m “FD2” windom-antenna.

After mounting the windom last summer it can say it works wonderfully, giving great signals on my SDR-receiver and giving great performance my station antenna too. The 6/4m-beam hasnt been used too much, but a number of 6m FT8-QSOs have been logged to verify that it works correctly. I still dont own a 4m capable transceiver yet, so a building project might be in order for me to fully test the new beam. This post was mostly written last summer, so this is just a summary to update on my current antenna setup.

Retro networking: Cisco 751 ISDN router

In travelling home for holidays, I found myself joyfully going through my collection of old computer equpiment still piling up here.

In one of the shelves I have a stack of Cisco boxes, one of which is a Cisco 751; a ISDN router with seemingly a good number of connection options for the time – 10Base2, 10BaseT and ISDN for uplink connectivity. Wondering what this unseemingly discrete box was used for, I whipped up my Google-fu and started looking up information about this thing – or so I thought.

A stack of Cisco-boxes

It seems most of the information of this thing resides in mirrors of old Cisco websites, luckily still hosted by some individuals for some unknown reason. All potential links pointing to Cisco officially are dead, and probably rightfully so since this thing is ancient.

Regardless of this, I found a old Cisco announcement of the 750 series, with its features as following:

….the Cisco 750 series is tailored fortelecommuters and small professional offices that require IP and IPXrouting over ISDN. In addition to offering ISDN remote access, the Cisco 750 series offers amodel with an external analog telephone interface to enable analog devices,such as plain old telephones (POTs), facsimile machines and modems, toshare a single ISDN Basic Rate Interface (BRI) line.

Nevertheless, I was intrigued enough to have at hand a fairly unknown router from the early 90s sporting 10Base2, as I think this would be a great gateway for my plans of a retro 10Base2 network.

Since there are literally no pictures of the Cisco 751 online (or just a few of the 750 series at all), I here present my contribution to making the world(-wide-web) a better place:

Cisco 751 front
Cisco 751 back
Cisco 751 bottom view

Inside, the box is filled to the cram with ICs and other goodies – way before any any integrated circuits doing the heap of the work of routing traffic.

Cisco 751 board – top view
Cisco 751 board – bottom view

My first and obvious obstacle was the missing original PSU. I remember having this thing for a while, though never being able to test it with the proper equipment. To the drawing board!

A quick drawing of the input circuit – a on/off button, the voltage regulator and the mini-DIN power connector

The input is first passed through the input switch, meaning the switch actually removes all power to the unit by switching off the regulator. The LM2576T voltage regulator generates 5V for the logic; there is another regulator inside the unit for generating the -9V from the +5V rail.

Cisco 751 PSU pinout – seen from the back of the unit

Above is a simple drawing for determining how to power the Cisco 751. There are 2 pins for GND and 2 pins for +VCC, which can be anything between 9 and 15 VDC.

Improvise, adapt, overcome!

Being home for the holidays, finding the correct test equipment proved difficult and I had to make do with I found- in this instance a 3.5mm DC jack and a couple of paper clips which were carefully inserted into the DIN-plug in the back of the box. On the first power up, afraid to let the magic smoke out, I started at 9V to minimize any possible damage to the unit.

But what do you know…. it works!

Green lights – a good thing!

The unit flashed up with green leds, starting the usual ISDN connection procedure just like it hadnt been 20 years since it was last used. Eager to find what secrets this time capsule has been hiding all these years, I grabbed my go-to Cisco serial cable from my bag to connect it to the serial port.

If I dont fit, I dont sits?

Yeah, that did not work. This thing precedes the blue-Cisco-serial-port era, sporting a standard DB9-plug. This would normally not be an issue as I have serial cables for days, but remember the part about being home for the holidays without my stuff? Yep.

If only one of these would work…

Even though I was able to grab a hold of more serial cables than most people have lying around at home, I could not find a single one up for the task. Some were null-modem, some were a completely different proprietary pinout.

How then?

Bingo! Simply a case of unscrewing the standoffs and mashing the USB-adaptor right into the plug.

Expectedely, I was met with a password protected prompt when booting the unit. Unfortunately all my password-recovery tricks were unable to get me into this thing as it preceedes most of any Cisco hardware. Adding the fact that there is no documentation for this thing online, I decided to leave it at that at come back to it at a later point.