Tuesday, 17 October 2017

LF Tests From WH2NXD / NI7J

For those of you with an interest in amateur LF work, you may be interested in the upcoming WSPR test  transmissions from Ron, WH2XND / NI7J, located in Phoenix, Arizona.

One of Ron's several experimental licences allows him to run as much as 10W ERP from 68-76 KHz. To generate this amount of ERP at 75 KHz requires a lot of power and I suspect that he will still be well under his licence limitations ... amateur-sized antennas are just not very efficient on these low fequencies.

Previous experiments a few years ago, at lower ERP, produced impressive results, as shown by one of the WSPRnet maps for an overnight session on 75.075 KHz.

Ron used one of the Hans Summers U3S transmitters to generate his LF WSPR signal, amplifying it with a 400W Hafler audio amplifier. This winter's tests will be at 800W, with a W1VD FET amplifier designed for VLF.

Ron's experimental licence also covers 470 - 495 KHz at a whopping 100W ERP and 130 - 140 KHz at 50W ERP ... some serious power.

You may also find Ron's interesting and well-illustrated website description of some experimental antenna work that he has been doing on MF, LF and what it takes to resonate a typical Marconi 'T' on these bands.

MF- LF 'T' Antenna At WH2XND

75 KHz Loading Coils!

Ron has tentatively chosen late November or early December for his 'almost' VLF tests and when the date and frequency are finalized, I will post the information here on the blog.

Wednesday, 11 October 2017

The KiwiSDR Online Network

Online SDRs (Software Defined Radio) continue to grow in numbers and popularity.

Listening on a receiver that is running in another state, province or country can fulfill a number of functions for you, depending on your particular interest.

The network that I have explored several times and one that works nicely with most web browsers (no software to download or 'extras' required) is the SDR.HU network of Kiwi SDRs ... just choose your receiver and away you go in a matter of seconds. It's all very slick and if you have never played with an SDR before, it affords a nice introduction to this amazing technology. Although it won't work with my ancient version of Internet Explorer running on Vista, it did fine with Firefox and even worked very well on my old I-Pad! Here is a 30-second YouTube video to give you an idea of what it looks like.

There are a huge number of choices from all over the world available on the Kiwi network. As I write this, there are presently 199 receivers online! Any particular receiver can support a maximum of four users at a time so if the one you want is full, simply check back later or go to your second choice.

Although all receivers have the same appearance online, not all will offer the same performance. Although most seem to cover 0-30MHz, I see at least one that is limited to the VHF range and several that don't go all the way to the bottom of the VLF band. The antennas used seem to favor wideband loops, both large wire styles and smaller active versions as well as active e-probes.

The best way to determine any particular receiver's operating performance is to try it out using test target signals that might indicate good performance from that location. If you're interested in BCB capability, test some of the European ones to see if they can hear any TA signals around sunrise in Europe. Many SWLs will use these receivers to compare what they are hearing at home with a receiver located closer to the suspected DX target signal. I myself found the network particularly handy for listening to my Tri-Tet-Ten transmitter on 10m CW a couple of years ago when the muf was much higher than it is nowadays. I'll be trying a few of them out this winter, listening for my 630m CW signal, at various locations.

Some of the receivers appear to offer good, low noise reception on LF, MF and the BCB but the vast majority are not DX machines oriented for this part of the spectrum ... this was the opinion of one notable BCB DXer who checked many of those in eastern NA as well as western EU. The jury is still out on the westerern NA receivers and those in the Pacific / Far East ... a worthwhile listening project when there is some spare time. Even though the receivers used on these lower frequencies did not usually offer stellar performance, they may be real workhorses within the ham bands or on the international shortwave bands.

It would be worthwhile to see some form of 'performance rating' or feedback page for each individual receiver. Although there is a 'vote' tally associated with each receiver it's not clear what this actually represents as receivers that have been online for longer periods would naturally have a higher tally.

A lot of additional information about the KiwiSDR network can be found here.

No doubt you can think of your own good reason to have a remote listen to some of the network's growing list of online receivers and put them to the test ... there may be some real treasures to be found.

Tuesday, 3 October 2017

A Weekend '29 Transmitter Project

A recent posting to the Yahoo AWAGroup, reminded me of a wonderfully simple transmitter that would easily get anyone on-the-air for the Bruce Kelley '29 QSO Party coming up in December. The AWAGroup is largely composed of '29 builders and operators and is often the source of much good discussion related to these activities.

When builders first tackle a '29 style rig, eligible for the BK Party, the first thought is often about finding an affordable tube that might make the transmitter a 'legal' entry. A suggestion of tubes and their relative availability can be found here in one of my earlier blogs. Although some of the tubes may not be typical junk-box items, one that is often very readily available and inexpensive is the '27' or the '227' / UX-227.

The '27 was a popular audio tube used in receivers back in the 20's and can easily be pressed into service as a self-excited oscillator on HF. When properly adjusted, the '27 can produce up to 4W of RF, more than enough for you to join the '29 fun a make plenty of contacts over the dual-weekend event.

Scott, WA9WFA, has produced a great article describing the construction of a 1929 Hartley oscillator using the 27. There is no need to utilize period-appropriate parts, other than the vacuum tube itself. If you are pressed for building time or just want to get something on the air, there's no need to be overly concerned about construction aesthetics ... there's plenty of time for that later, and besides, the uglier ones often work and sound the best!

WA9WFA's 27-Tubed Hartley

Power supply requirements for the transmitter are pretty minimal and could even be an old receiver supply ... something that delivers 250-300 VDC at 35ma. An effective way to easily double the power of this transmitter is to add a second tube in parallel with the original one, providing your power supply can supply the extra current (~35ma) required. Although Scott's information describes an 80m Hartley, there is no reason why you could not wind a coil for 40 or for 160 and take advantage of any activity on those bands as well. Like most of these link-coupled outputs, you'll probably squeeze a little better efficiency from the circuit by adding a variable capacitor (~365pf) in series with the pick-up link and the hot-side of the coaxial feedline.

Nick, WA5BDU, wrote his description of building the 27 Hartley which can be found here. He also includes information on running the 2.5V filament from a 5V transformer.

WA5BDU's 27-Tubed Hartley
ABØCW uses two 27s in parallel for the oscillator section of his 1929 MOPA. Details of his interesting Hartley can be found here.

ABØCW's Parallel 27s

As further proof that you don't need a lot of power to have fun in the 1929 BK Party, here is the rig that Kevin, WB2QMY, used when we worked on 80m CW. His little TNT, just barely putting out 2W, made it all the way from New York!

WB2QMY's 80m 2W TNT
When it comes to the BK ... if you build it, they will come. Hopefully you can join the fun this winter as well.