How sensitive can headphones be?

Having made several short-wave crystal sets in my time I have nearly always used the little "deaf aid" very high impedance crystal earpieces as the acoustic transducer. I thought these were very sensitive being able to copy HF AM signals down to around -55dBm to -60dBm. However I recently read somewhere that with the old WW2 DLR5 low impedance headsets one could hear an applied audio signal as low as 2uV (-101dBm), which is remarkably low.  

So, I began to wonder just what ARE the best headsets to use if one is after the maximum efficiency converting an audio frequency electrical signal into sound pressure in the ear?

This graph (from Wikipedia) shows the sensitivitity of typical humans at different ages. Someone of my age (63) is likely to be less able to hear as low as someone aged 30 years.

As some of these old military surplus headphones can be hard to find nowadays in good condition, I wonder what is the most sensitive headset/earpiece that can be bought new "off the shelf". Any ideas please?

Dropbox Problem

When my grabber is running I use Dropbox to automatically upload the captured image to a location on the net where anyone can see the image. Recently Dropbox has been doing something wrong and when I try to launch the program I get an error message (see image). I have tried EVERYTHING to fix this, to no avail so far. Has anyone else had this issue? I looked on the Dropbox website (not too helpful), tried running Ccleaner to see if the registry entries were faulty (no luck), reinstalled the software (about 10 times now in different release versions) and deleted each when the same darn message appeared.

Help!

New beacon chips arrive

Today my new KID2 pre-programmed beacon ICs arrived from www.k1el.com . These are for use in my VLF, 136kHz, 500kHz and 481THz beacons. With 7 pre-programmed messages in 10wpm CW, and various QRSS speeds these are ideal. I have used these before and been very satisfied.  See http://k1el.tripod.com/files/kid2man.pdf for more details of the ICs.

Laptop/Netbook Reliability

Investing in a new laptop or netbook can be a tricky decision: getting the right price, spec, performance and reliability. My Dell laptop failed a year or so ago (keyboard) but I was able to repair it by buying a new keyboard via eBay and following some good fitting instructions found on YouTube.  My wife's school laptop LCD screen just failed suddenly when it was in use on her lap with black "cracks" appearing as if the whole thing had been dropped. This was repaired under warranty thankfully. Then you hear of hard-drives failing.

Today I came across an interesting page giving some reliability statistics for laptops and netbooks. Apparently Asus and Toshiba make the most reliable ones. The paper is by a company selling extended warranties, so they will be keen to show that it is worth buying one. Nonetheless I think the stats are fair.

FT-450D hum: a good response from Yaesu

Last night I wrote to Yaesu UK about the FT-450D hum issue and got a very fast and very helpful, response from Paul Bigwood their Technical Sales Manager. All credit to him.

I will paraphrase Paul's reply below.

He confirms the hum problem has been recognised and that it doesn't affect all radios. Those it does, are only affected in voice modes, when the display brightness is reduced below its normal maximum level. The level of hum is generally low and is usually only noticeable when the received signal strength is high [i.e. with local stations], DX stations don't normally hear it.  He says that steps have been taken to resolve the issue and product shipping into the UK dealers since the beginning of the year have a modification to resolve it. He told me that if I purchased one that does suffer from hum under the circumstances as above, then it can be returned to Yaesu for updating under warranty.

He went on to say,

"Please rest assured that Yaesu does care about its products, their reliability and performance. We certainly look to resolve any problems as soon as they become known to us.  The FT450D is a splendid radio, having done excellently at the T32C DXpedition last year when over 200K QSOs were made with no reports to us of any hum problems."

I thought this was an excellent and totally professional response. Yaesu is a first class manufacturer and it is reassuring to see they have taken on board the hum issue in this otherwise excellent little radio and have now taken steps to properly fix it on new build units.

137kHz transverter bites the dust

Having re-erected my 80m loop antenna I was about to reload OPERA and give it a try now it appears more stable. I ran up the transverter on WSPR to check all was well only to have the power supply suddenly take around 20A and shut itself down.  I think the MOSFET PA died on me. All being well I will get this fixed next week when my grandson goes back home again and have another try.

Netbooks

For many years I used a little Asus EEE PC701 (7 inch screen) netbook running a pre-loaded Linux OS. This was ideal for basic net surfing and emails, but it lacked the flexibility of a Windows OS when looking for ham radio software. At the moment I am looking at a possible replacement that I can use for general web browsing and also to run WSPR, OPERA and hopefully Spectran and Spectrum Lab freeing up the main PC. Such a small netbook would also be useful for field use with VLF tests, lightbeam experiments etc.

It is quite amazing what £200-250 will buy today. My first laptop cost me £1499 back in 1998 and the performance was nowhere near that of even my little Asus EE PC701!

My inclination is to buy another Asus machine unless someone can give me good reasons to choose another make.

A new meteor scatter mode

http://www.dk5ew.de/2012/01/13/psk2k-a-new-meteorscatter-mode-by-dj5hg/

This webpage gives details of an interesting high speed MS mode from DK5EW. There is also a Yahoo group to discuss this: see http://uk.groups.yahoo.com/group/psk2k/

"PSK2k is high speed meteor scatter software written by Klaus DJ5HG (Prof. of Computer Science at University Hamburg).  It allows 2 way MS QSO’s to be conducted with any suitable transceiver/PC/soundcard combination.

PSK2k is fully error correcting and call specific in operation so you will only see the QSO in progress and any non-QSO CQ or QST text. All other transmissions (other people also in QSO) are discarded. This allows multiple QSO’s to take place on a single frequency.

PSK2k can be operated in fully automatic mode if required. This enables QSO’s to be completed fully automatically without user intervention. Important advantages are that long term testing can be done, on QRP power for instance, without having to sit an monitor every period."

Philips FM321 70cm mobile

The very first FM synthesised 70cm rig in the UK was made by Philips in Australia and was called the FM321. This 4W mobile was based on the very similar FM320 designed for the Australian UHF CB band. I owned an FM321 for a couple of years back in the early 1980s and really enjoyed using it on the UHF simplex channels and repeaters. Ergonomically it was excellent with simple up-down channel change and a decent volume control. It is a pity rigs are not made as simple as this today. No memories, no fuss.

From the home QTH and with just a hand rotated small vertical yagi I could work some impressive DX on FM on some days. That's the thing about 70cms: propagation changes within hours and often in very localised directions. When there was plenty of simplex activity it was very interesting watching propagation change and the maximum range change from maybe 30 miles to over 100.

WRC-12 Radio Conference (Jan 23 - Feb 17)

This most important international frequency revision conference takes place Jan 23th - Feb 17th. As always, the amateur service can never be certain of the outcome with a possibility of precious spectrum being lost to other services. However, this time there is a good chance that we will GAIN a new amateur MF band somewhere between  415 and 526.5kHz. The most likely outcome is a band near 480kHz around 8kHz wide. 8kHz of spectrum would allow much more experimentation, especially if this allocation was world-wide. This would supersede the special permits around 500kHz allocated in some countries.