Archive for the ‘k3’ Category

An interesting Problem

Sunday, March 14th, 2010

Recently I Dug out an old headset that I had leftover from my Pro-audio days. It’s A Beyerdynamic DT-109 which is a very nice set of Headphones with a good quality Hyper-cardoid microphone capsule. Ideal for rejecting shack noise and with a response curve well suited for Good Quality communications audio. Data sheet as a PDF here

DT109

The first issue I had was that the audio level out of the DT-109’s microphone is rather low so I constructed a premap based on this Design. This is powered by the 5V bias that is available from the K3 for driving Electoret condenser microphones. I constructed this preamp on a bit of Stripboard and mounted in a small herb tin I stole from the kitchen.

This worked very well, at least until I turned my amp on.  With my Acom1000 on, even in standby I was hearing a lot of Hum. At first I though it might be down to a ground loop problem, I had taken care to ensure that the ground on the radio side of the preamp was connected at the point where the wire enters the tin but the Microphone side floats above ground and is decoupled by a Capacitor (C1) first I tried a larger value to no avail, Then I tried adding a 1:1 audio transformer and grounding the headphone side. This made matters much Worse.

Then the penny dropped! The issue was due to the magnetic field from the Power supply of the amplifier.  Where I had the amplifier positioned was around 1metre away from the the Microphone element when I was sitting in the operating position and the microphone had it’s back side facing the amplifier, Maximising it’s sensitivity to the magnetic field

I hooked up an old solenoid coil to my portable scope and did some sniffing around to get an idea of the magnitude of the field. I discovered that the field was pretty intense in the vicinity of My K3s and their transformer coupled Audio lines so it seemed prudent to relocate the amplifier. Interestingly the Magnetic Field contained a lot of harmonic energy, Due I suspect to the rectifiers in the Power supply. The power supply is contained in the right-hand side of the Acom1000 so the answer was to move the amplifier from the left  of the operating position to the Right. Not an ideal location for ventilation in my shack but  I had some aluminium Ducting that I was able to use to improve the exhaust airflow

Scope_shotSolenoid

With the amplifier on the right the power supply is a little further away from the microphone element but this position also means that the  side of the microphone capsule is pointing towards the Amplifier and in this position the element is less susceptible to picking up the Magnetic field. This position also places the  k3’s Line in / out transformers a lot further away from the field which should  prevent issues with Digital modes.

The DT-109 now works wonderfully with the K3, I use the following EQ settings

50Hz  -16, 100Hz -16, 200Hz -8, 1.6KHz +3

The New Shack layout

73

Brendan EI6IZ

Posted in Audio, k3, shack | No Comments »

K3 Line output plots

Tuesday, September 2nd, 2008

I took a couple of plots of the K3’s Line output compared to the Headphone output

For these plots the K3 was connected to a wideband noise generator. measurements were made with my Delta 44 soundcard

The line out is in green. the Blue trace is the headphone output with the volume set to match the level of the line out

The first plot is with the line output level set to 100, the second plot is with the line output level set to 5

Posted in k3 | 3 Comments »

KRX3 the elecraft K3 Sub Receiver

Saturday, July 19th, 2008

My KRX3 arrived yesterday and after about 4 hours of work It was fitted into my K3. For those of you that don’t already know The KRX3 adds a second receiver of equal specification to the primary receiver to the K3

Generally sub receivers are useful to help find out where the dx station is listening in the pileup, to search for multipliers whilst ‘running’ in a contest or to monitor a second band.

The K3 with the KRX3 fitted has another ‘neat trick’ up it’s sleeve. If the KRX3 is configured with the same filters in at least some of the slots as the primary receiver it can be used for Dual antenna diversity reception. In this mode the Sub RX tracks the tuning of the main RX. I have been using diversity reception for a number of years for tropical band broadcast Dxing with my Racal RA-3702 however the K3 is the first amateur transceiver I have used that is actually capable of doing diversity reception well.

Icom’s Flagship 7800 fails miserably in diversity on two counts. Firstly the main and Sub RX have a small but constant frequency offset making it very tiring to listen to, secondly the tuning of the main and sub receivers cannot track.

On the Elecraft k3 tuning tracks both receivers (when linked) RIT also applies to both receivers making the k3 very easy to use in diversity mode.

Diversity holds a lot of promise for weak signal DXing where using 2 separate antennas can help reduce the impact of fading, QRM and noise

Diversity is also very useful for enhancing the ability to pull individual calls out of large pileups

Here is a 5 minute audio clip of the K3 in Diversity mode. For a better idea of how useful this is listen with headphones on.

here is the YR2TOP beacon on a noisy 160m with K9AY loops on the left and a beverage on the Right
filter bandwidth is 150hz this time
160m_beacon_k3

Here is a clip of an SSB pileup on 20m Here too diversity reception helps to separate the callers
k3 20m ssb diversity

Posted in k3 | 8 Comments »

Cheap Headset

Sunday, May 11th, 2008

One of the nice things about the elecraft K3 is the support that it has for a very wide range of microphones. The rear panel mic connector is directly compatible with computer headsets once the bias voltage is enabled to power the electret condenser element.

My normal headset is a home brew one based on the bias circuit that is normally used in Icom hand mics. This simple circuit is published in the user manuals for most modern Icom Radios. The manuals can be found on line on the Icom website.

Recently, however I have been using a little headset that I bought on Ebay for 1 pound Sterling ( about 2 US dollars.)
I have been getting truly fantastic audio reports on this headset when used with the K3. It’s a little bit flimsy but it’s very light and easy to wear, It simply loops over one ear.

Vox on the K3 is fantastic but I prefer to use a footswich for PTT control.

Lots of Ebay vendors have similar products and any computer store will sell you a ’skype’ headset. Before you spend ‘proper’ money on expensive ham radio branded products, try a cheap computer headset. You may be very pleased with the results.

K3 Headset

Posted in k3, shack | 1 Comment »