Another 472/500kHz transverter built stateside

Just got this nice email from John WA3ETD/WG2XKA who has successfully built another copy of my 472/500kHz transverter.

"Hi Roger,

I completed your design XVTR Saturday here, on the air on WSPR last evening had eight uniques and flawless operation.

I slightly modified the PA by adding the gate resistor and diode, as well as driving the FET via a cap. I only had surface mount IRF-510, that is the raised, floating copper heatsink that sits on two tiny standoffs at drain potential.

Thanks again for publishing your design!  PIX attached.

73,
John WA3ETD / WG2XKA"

WG2XKA's version on my 472/500kHz transverter

Rotatable dipole or HF halo?

DES Rotating Dipole

A new antenna is being advertised by InnovAntennas: a compact rotatable 15, 10 and 6m dipole with droopy ends so that the overall length is no greater than a single 10m dipole. It is called the DES-Rotating Dipole. The image on the right (from the InnovAntenna website)  shows the neat arrangement which can be fed directly from 50ohms. Without lossy traps the power rating is at least 5kW, rather more than I would ever need.

Now, neat though this is, I question whether it is really worth the expense. At this stage I have no idea of price but I would expect somewhere between £50-100? My simple Homebase-10 wire halo is MUCH smaller because the 10m dipole is arranged in a square. A 6m halo can be nested inside very easily and fed with the same coax. To add a 15m halo would only increase the size by 50%. Unlike the Cobweb antenna, my simple design could be assembled as a 3 band version for less than £15 with all new parts.

Homebase-10 10m halo

How much down is the halo compared with the nested dipole?  In most directions, apart from a tiny segment in the direction where the ends of the halo meet, less than 2dB. What is that in S-points? Hardly noticeable at all at about 1/3 of 1 S-point.

A dipole, if rotated, does have the advantage of being able to null out interference but I am not sure this is such a benefit. For me, it is either something like a horizontal halo which tends to be a "quiet" antenna picking up little local (vertically polarised) man-made interference or a small beam which would have some gain and directivity. However, the latter will only add about 0.5-1 S-point in signal level and, time you buy a decent rotator and the beam, you will have paid 10-15 times more for the privilege. A beam does add directivity and interference rejection, but is much larger. For me it is a "no brainer".  My simple little halo has allowed me to get QRP reports on SSB, CW and WSPR from all over the world. It is simple and works well.

Lesser Chirpy reaches Cyprus

No QSOs this morning yet but a RBN report from 5B4AGN in Cyprus with the 80mW lesser Chirpy 10m CW transceiver to the Homebase-10 halo. This is the first time I've looked for RBN reports with this tiny transceiver.

Reverse Beacon Network report for 80mW Lesser Chirpy

When I got back from my grandson's birthday party in London in the late afternoon I put out about 10 CQs on 28.060MHz with the rig, but no QSOs or RBN reports. I shall try again during the week.

Ten-Tec Argonaut VI - has it died?

The Ten-Tec website still has no information whatsoever (that I could find) about the Argonaut VI which was supposed to be ready to order by now. I'm wondering if, despite talk of pilot runs and the like, Ten-Tec has had second thoughts and decided not to release it after all.  I've just written to Ten-Tec to find out what the news is. I've asked when it will be available and at what price. We'll see what comes back from the sales team.

Solar prediction update

NASA has slightly modified its predictions for the current sunspot peak showing the peak month as May 2013 with a 95% prediction of just over 100. The smoothed number will peak later.  Although conditions will gradually deteriorate after the peak, the monthly sunspot number is still expected to be over 60 right until mid 2016. See http://solarscience.msfc.nasa.gov/images/ssn_predict.txt . The evidence in the short- term looks somewhat less good, but things can change rapidly.

So, get on the air, especially on the higher HF bands and enjoy the good times!

Date/Month 95%   50%     5%

2012  11  96.1  68.7  41.4
2012  12  97.2  69.7  42.1
2013   1  98.2  70.5  42.8
2013   2  99.1  71.2  43.4
2013   3  99.8  71.8  43.9
2013   4 100.4  72.4  44.3
2013   5 100.9  72.8  44.6
2013   6 101.3  73.1  44.9
2013   7 101.6  73.4  45.1
2013   8 101.8  73.5  45.2
2013   9 101.8  73.5  45.2
2013  10 101.8  73.5  45.2
2013  11 101.6  73.3  45.1
2013  12 101.3  73.1  44.9
2014   1 100.9  72.8  44.6
2014   2 100.4  72.4  44.3 

Delay getting 472-479kHz released in the UK?

On the GQRP Yahoo group today Colin, G8FRA/M5FRA, posted this message regarding the release of the new 472-479kHz band in the UK. If his information is correct, there could be some delay in the bulk of UK amateurs gaining access to the new MF band. This would be a great pity.

"Roger,

From what I learned by talking to a couple of people at Newark (RSGB and OFCOM) we will not get the new allocation in Jan 2013. Those with existing SRPs will have them changed to remove 500kHz and add 472-479kHz. I asked when applications would reopen and there was no date for that. Evidently OFCOM have to consult before there can be any changes to the license schedule and have been too busy with the Olympics to make any progress on that. I did suggest that the RSGB should come clean as anybody who has spent time and money on new equipment might just be a bit disappointed.

Colin - G8FRA/M5FRA
m5fra.org.uk"

If this information is correct, then why is our national society, the RSGB, not making this public? I have written to OFCOM and the RSGB asking for more concrete information.

10m Lesser Chirpy in a new box

Lesser Chirpy (should be No Chirpy!) 10m transceiver

At last I've got around to putting my Lesser Chirpy ultra simple 28MHz CW transceiver in a case. I've added an extra switch so I can listen on another RX if conditions are such that the internal RX struggles, although even with my 64 year old ears I can clearly hear better than -100dBm signals on Lesser Chirpy. Offset is set at about 700Hz between RX and TX. The FSK keying is a bit odd - there is only around 100Hz shift between carrier on and pseudo off (i.e. shifted) but there is zero chirp. This is now a seriously useful transceiver, albeit very very simple. Power out on this sample is around 80mW, so I believe this is certain to span the Atlantic in the next few days, if only to be spotted on the Reverse Beacon Network.

Lesser Chirpy cased

I have not got an internal low pass filter on this model. One should be added between the rig and the antenna to ensure low 2nd and 3rd harmonic levels.

Ferrite Rod RX antenna for 472kHz

 In an attempt to overcome my high LF noise level, today I made a small ferrite rod antenna and preamp for 472kHz which I've been trying out on RX. The ferrite rod was just a small 10mm diameter 60mm long rod (i.e. it is a small ferrite rod) tuned with a 365p variable capacitor and fed into an MPF102 gate at high impedance with the output fed to the FT817 via an emitter follower. At the moment the rod is sitting on the bed in the shack. Despite this, it is picking up WSPR from DK7FC.

I shall have to try a larger ferrite rod next and try placing this remotely in the garden away from noise sources. For a first attempt this is encouraging.

The prototype used to receive DK7FC and G3ZJO

UPDATE: later I tried the 60mm ferrite rod and preamp on 500kHz and copied G3ZJO on several occasions. 

MF "swish, swish, swish" interference

In recent months I've been suffering from man-made noise on MF which was not there before. I've a constant S8 noise floor now (it was around S1-2 before) and as I tune from 300-500kHz I get a rapid  "swish swish swish" every few hundred Hertz. I think there are frequencies where it is stronger but the new 472-479kHz is BAD, although I still manage WSPR decodes from DK and SM. For CW it would be just about impossible.

Now, I haven't yet tried to systematically work out what this is yet and nor have I tried a small external loop on RX or an E-field probe down the garden.

Before I start to investigate, does anyone have a clear idea what this rapid "swish swish swish" QRM is likely to be? I don't think the source is in my own house and on one side the neighbour's house is currently unoccupied. I have tried the obvious (turning off lights and SMPSUs in my own place) with no success.

Any knowledgeable help would be much appreciated.

Man-made interference at MF and LF is a critical consideration for newcomers. I hope that a new version of the RSGB book "LF-Today" (if one is planned) will give some information on how to search out such sources and some strategies for how they might be mitigated.

Building requests

In the last 24 hours I've had a couple of requests from people asking me if I'd build some of my projects for them. One person asked if I'd build them a Pipit 15m transceiver and another a 472kHz transverter. Regretfully I had to say sorry that I could not.

It is not that I don't want to. Rather, it is because I don't have enough spare time! I've so many projects on the go currently, and a stack more in my head waiting to get started, as well as trying to live a normal family life doing the usual chores. Then we have the grandchildren who take time, not that we mind this at all.  So, please do not ask if I can build projects for you. I always try to help with advice and suggestions when asked - I try to respond within 24 hours unless I am away -  but I do not want to do building.

Quite a few of my projects would benefit from a small PCB. This is also something that I rarely get around to because I've already moved on to something else. There is probably a small business possible, if I was inclined, designing projects, making a PCB and selling kits. This is unlikely ever to make me rich though and I'd prefer to be a source of ideas instead.