E-field probe mag-mount now built

This morning I decided that it would be better to build the E-field probe for 137kHz RX at the base of the whip directly on the mag-mount base rather than inside the vehicle and having to tune out the cable capacitance. This way,  the cable capacitance is no longer an issue. I built the E-field probe into a small plastic box and arranged it so the whole unit attaches to the mag-mount using a PL259 plug in the bottom of the unit. Radio 4 on 198kHz is an S9+ signal with the mag-mount sitting on the bedroom window-sill with around 10 inches of whip. It appears to be working well.

The present design is a poor man's PA0RDT probe but using an MPF102 and a 2N3904 rather than the better devices used in Rodolph's high IP2/3 design. I may put a tuned circuit in the FET drain to increase the gain at 137kHz and reduce the gain outside the band. I will experiment with this before going out in the car.

Currently it is snowing continuously here, so road testing the EFP and checking coverage of my QRP 137kHz CW and QRSS3/30 beacon will now have to wait until later in the week.

UPDATE: I have modified the EFP so that the FET output comes from the drain with a drain tuned circuit tuned to 137kHz. I have the source resistor not decoupled initially but will consider adding this if I need a little more overall gain as the barefoot FT817 is very deaf on 137kHz.

A mag-mount as an E-field probe for 137kHz

Next week, assuming the snow has gone, I want to drive around the local area to plot the polar pattern of my earth-electrode antenna working on 137kHz.  My 7-8W beacon transmitter can send a range of QRSS and CW messages, so I want a way of driving to different places using my FT817 fed via a preamp and measuring the S/N using Spectran whilst remaining inside the car.

Portable RX loops are fine, but these are directional and need to be set up each time a measurement is taken outside of the car.  Ideally I need an omni-directional RX antenna like an E-field probe. So, I'm looking for a way to drive to a spot, take a quick measurement from inside the car, then move on; a loop works, but when it is -2 deg C outside and the ground is icy, it is not ideal.

Either I put the electronics for an E-field probe right at the base of the mag-mount (mechanically not ideal) or I have the electronics in the car and somehow tune out the coax cable capacitance.  At the moment I am still experimenting to find an arrangement that works with good sensitivity by checking the strong Greek commercial signal just outside the 137kHz band.

Based on 472kHz results, the earth-electrode antenna behaves like a loop with loop-like directionality. I 'd expect to see the same pattern on 137kHz.

K7AGE video of his KX3 build

Randy K7AGE has done a wonderfully amusing video of him building his Elecraft KX3. I won't spoil the fun, but recommend you watch it and see how it is done.

Square trade eBay Warranties - any good?

Just looked on eBay for various amateur radio items and noticed the Albrecht AE2990 10,11,12m handheld on sale from various UK suppliers from around £150. Now also shown was an optional 3 year warranty - see http://pages.ebay.co.uk/safetycentre/buyingwithconfidence/warranties/index.html which cover failures to the device outside the manufacturer's warranty period. So, for less than £200 you can have a multimode HF handheld complete with 3 yr warranty.

Peace of mind 3yr warranty for £27 - too good to be true?

My question is this. Has anyone here bought an eBay item with one of these warranties - they seem to be widely offered - and had to make a claim?  It sounds almost too good to be true. These warranties are also available on low cost VHF/UHF handhelds as well where the warranty cost is only around £8-9, which looks remarkable value if the product fails. This is as long as the warranty is a decent one that is honoured and the small print doesn't render it worthless. They also offer a 5 day repair or replacement service.

Mixed results with WSPR-X and WSPR-15

The new version of WSPR works well with plenty of reports given and received on 472kHz with it over the last 12 hours using the 2 minute version (as before but now with a waterfall and better interface), but mixed results on the slower 15 minute slot WSPR-15 which can detect much weaker signals.

My problem is TX drift over a long 15 minute transmission. My small 10W transverter is in a tiny plastic box. When using a 2 minute transmission the PA barely gets warm so there is little heat transferred to the crystal oscillator. With the much longer TX burst the PA warms more and the crystal warms up several degrees, moving the oscillator frequency by some 10s of Hz. So, although I was able to copy signals in WSPR-15, I was not able to be detected by others overnight. There are also far fewer stations monitoring yet on WSPR-15.

The solution is to rebuild the transverter into a bigger (metal) box with (a) better heatsinking so the heat rise with a mismatch is lower, (b) a slightly more efficient PA - problem here is with weather changes the antenna match goes off optimum sometimes and the heat rises as it the PA becomes less class E, and (c) put the conversion frequency oscillator physically further away from the PA, currently it is less than 10cm.

If I fix these issues and am sure that I transmit a more stable signal in the narrower (25Hz wide) WSPR-15 slot then I have a better chance of succeeding with the more sensitive version.  With another 7-9dB S/N detection improvement, my signal could reach some of the more distant stations like TF3HZ.

Iceland get the new MF band

Icelandic radio amateurs have been granted access to 472-479 kHz and temporary permits for 1850-1900kHz, 5.260-5.410 MHz 70.000-70.200 MHz have been extended.

WSPR-X and WSPR-15

A note from Joe Taylor K1JT informing us about a new version of WSPR.

WSPR-X and WSPR-15

Wed Jan 16, 2013 8:23 pm

Some of you may be interested in trying WSPR-X, a new version of WSPR that includes the slow mode WSPR-15. WSPR-15 uses 15-minute T/R sequences, rather than the standard 2-minute sequences; at MF and LF it is 9 dB more sensitive than WSPR-2, decoding signals as weak as -37 dB in the standard 2500 Hz reference bandwidth. WSPR-15 is not recommended for use at HF: the tone spacing is only 0.183 Hz, less than the Doppler spreading typical of many HF paths. The main intended application for WSPR-15 is for very difficult paths at 137 kHz and the new 472 kHz band. It may be interesting to try on 160 meters, as well. Note that the recommended WSPR-15 sub-band is a 25 Hz slice just above the 200-Hz WSPR-2 sub-band, i.e., 1600-1625 Hz above the standard "dial Frequency". This will be handled automatically if you set up WSPR-X in the normal way.

A brief online User's Guide for WSPR-X is posted at
http://www.physics.princeton.edu/pulsar/K1JT/WSPR-X_Users_Guide.pdf ,

and the Windows installation file is posted at
http://physics.princeton.edu/pulsar/K1JT/WSPRX_07r2948.exe .

At present, WSPR-X does not support I/Q audio (for use with direct conversion receivers and transceivers) and does not do “band hopping”. Otherwise most familiar WSPR features are present and working well.

For software enthusiasts: Unlike older versions of WSPR, the user interface of WSPR-X is written in C++ and the Qt programming framework. My expectation is that this shift will make for easier development and program maintenance in the future. At present a click-to-install package is available only for Windows. Source code for WSPR-X is available from the open-source SVN repository at berlios.de. Anonymous checkout of the full WSPR-X source code can be accomplished with the command svn co svn://svn.berlios.de/wsjt/branches/wsprx

User comments, suggestions, and bug reports will be very welcome!

-- 73, Joe, K1JT

Band Plans and AM - Feb 2013 RadCom

In the new February RadCom that just dropped on my mat at lunchtime there is a copy of the band plans for all bands from 136kHz to 134GHz.  What I fail to understand is why does the RSGB appear so anti-AM?

For many years now there has been a clear choice for an AM centre of activity on 144.55MHz. The RSGB has been made aware of this on many occasions and yet still we have a (begrudging) footnote, just about visible if you look hard, saying this is where to look. Even this comment ends with, "although this frequency is not officially recognised within the 2m band plan". Why not? We have a FAX calling frequency listed and goodness knows how many DV Internet Voice Gateway frequencies listed, yet we cannot be allowed an official AM centre of activity properly listed! AM is not a common mode these days, but those who enjoy the mode need to know where to meet on the band. The RSGB is giving no help at all here.

I also get frustrated with the 10m band plan where AM is again almost treated as a disease. Most AM activity has been in the 29.0-29.1MHz segment for years now: this is THE part of the band where AM users congregate, yet the all-mode section with up to 6kHz bandwidth does not start until 29.1MHz upwards! Does no-one who creates these band plans actually listen to see what actually goes on? In the last 30 years I have had many AM contacts on 10m and not one outside 29.0 - 29.1MHz.

So, next time you consider the band plans, please:

(a) Add an AM "centre of activity" frequency into the 2m band plan - it is 144.550MHz in case you don't know.
(b) Show 29-29.1MHz as the AM sub-band in the 10m band plan.

Back on 137kHz TX

QRSS and CW beacon TX for 137.685 kHz

Today I went into the shack with the intention of making a new transverter for 137kHz based on my recent design for 472kHz.

Instead, I ended up building a new CW, QRSS3 and QRSS30 8W beacon transmitter using an IRF640 PA device. This evening and overnight the beacon will run QRSS3 on approximately 137.685kHz and I have requested reports and screenshots.

The antenna being used is my 20m spaced earth-electrode pair set-up used very successfully on 472kHz last weekend. On 137kHz signals are much weaker than on 472kHz, so I await reports with interest.

The whole unit runs quite cool when housed in a plastic box. Switches on the front of the boxed unit allow up to 7 pre-programmed messages to be beaconed at varying speeds. As normal, I use the K1EL beacon chip for the beacon message generation. The signal source is a 3.579MHz crystal in a divide by 26 circuit implemented in a PIC like device and kindly supplied to me by a French amateur Francis F6HSI a few years ago.

eQSL cards

Brazilian QSL card received via www.eqsl.net

To be honest I'm not very good at QSLing.  In years past I would regularly write out QSL cards and send them out to the bureau and look forward to the next batch of cards. These days I do send out some paper cards, but not that many. Instead I tend to use eQSL cards instead, but I was way behind with reviewing incoming QSLs so this evening I spent an hour or so getting up to date. I rejected a few cards - one for a WSPR "QSO" where what had really happened was an exchange of reports via the WSPRnet database, and the other for a voice-over-internet QSL with a JA station.

Checking my totals I see that I have 55 countries confirmed by eQSL cards. All these will be with 2.5W or less on all modes, mostly SSB on 10m and 6m. Many of my DXCC countries pre-date the eQSL era and I have not been that active in DXing as such in recent years, apart from the occasional contest like CQWW SSB, which I enjoy with QRP.  As you know, I prefer to carry out crazy experiments somewhat on the edge of sanity on strange bands with odd antennas instead!