ZL2UHF 2m Beacon now running JT4D

[ZL2BKC]

After over 30 years of near continuous operation the ZL2UHF 2m beacon on 144.275 MHz developed a serious fault at the end of last year. Given its age it was decided replacement was the best option, and in Janurary a replacement beacon was installed and soak tested using the old FSK-CW mode.

On Feb 28th the JT4D digital mode was enabled, which now opens opportunities to experiment with weak signal digital modes using the popular WSJT software.

The new beacon consists of a ZLPLL board driving a 2m power block with a controller baord containing a more powerful Atmel micro and GPS receiver to get exact timing which is a requirement for all WSJT modes.

JT4D is being transmitted for the first 47 seconds of each minute followed by a CW ID. Note that the lowest JT4D frequency is zero beat for 144.275 MHz

For anyone interested JT4D was chosen over JT65 mode as it was easier to generate with the chosen PLL, and it will generally be more successful for those with lower stability radios from the 70's and 80's era. It also seems to be more popular for beacons in Europe so seemed like a logical place to start.

Some pics of the beacon during its construction phase before covers were installed shows its simplicity (and potential to add other bands in the future...) :

Inside view of beacon controller

PA Board closeup

As an interesting experiment I tested a screw driver in the back of my FT817 and got -9dB decodes I ended up with a short piece of wire and progressively started to trim off 1cm at a time until decodes stopped at -16dB. After increasing the WSJT audio gain (right hand slider in the waterfall screen and disabling AFC) I can now decode the beacon at -22dB and -23dB (some at -24 but not as reliable)
The scary thing is for most of this experiment I was just listening to static!

So far the beacon has proven to be stable enough that planning has started to deploy a similar upgrade at Waipuna Ridge for the 144.271MHz ZL2WHO/B 2m beacon. Work is also underway to add a 1296 beacon at Waipuna so next summer DX season there should be a number of new and exciting signals to decode.

For additional information about the controller you can read more at http://zl2bkc.com/projects/multi-beacon-controller/

73,
Wayne

[ZL2BKC]

Also a big thanks to those whose who have spotted the beacon since the upgrade. One challenge is the VKLogger beacon spot does not allow digital modes, but most are using their inititive by placing JT4D and the decode string in their VKLogger spots.

Adam may want to consider how to cater for this in the future......

73,
Wayne

[VK2KYP]

Great result, I hope to hear this beacon one day
Gary VK2KYP

[VK3HZ]

Hi Wayne,

Great effort with the JT4 beacon. Hopefully I'll get to hear it one day!

Just to clarify, you say it's running JT4D with the lowest tone on 144.275 MHz. At the audio level, JT4 uses 4 tones centred on a frequency of approx 1270.5 Hz. For JT4D, the tone spacing is 39.4 Hz, so the lowest tone would be at an audio frequency of 1211.4 Hz. So, to get a DF of 0 on WSJT, the radio would need to be tuned to about 144.273 789 MHz.

Also, what message is the beacon transmitting?

Regards,
Dave
VK3HZ

[ZL3TY]

Here is a typical decode:

054500 6 -24 -0.6 -39 46 * ZL2UHF RE78 1 0 A

I started looking for the beacon on Sunday morning and found that tuning the radio to 144.273,6 MHz works. The path from here is almost all over mountainous country and I have not yet heard the CW id part of the transmission sequence. The JT4D decodes range in strength from -17dB to -25dB.

Thanks Wayne, this will be very interesting to see how the signal varies over time.

Bob ZL3TY

[ZL3RC]

Dave,
Just been checking the JT4D frequency and at 144.273 789 Im getting a DF of 26

Considering I don't have the 847 locked in any way I think your frequencies are pretty much on the money.
Its been a lot stronger down this way since the update so you never know some day you may copy it over there.
Have to get Mark to update his keyer/exciter on the 144.271 ZL2WHO/B as its higher power would be useful in your direction.

Roger.

[ZL2BKC]

Hi Wayne,

Great effort with the JT4 beacon. Hopefully I'll get to hear it one day!

Just to clarify, you say it's running JT4D with the lowest tone on 144.275 MHz. At the audio level, JT4 uses 4 tones centred on a frequency of approx 1270.5 Hz. For JT4D, the tone spacing is 39.4 Hz, so the lowest tone would be at an audio frequency of 1211.4 Hz. So, to get a DF of 0 on WSJT, the radio would need to be tuned to about 144.273 789 MHz.

Also, what message is the beacon transmitting?

Regards,
Dave
VK3HZ

Hi Dave,

Others have pretty much answered your questions. The reference uses a OCXO and at some stage I plan on measuring the exact frequency as it will probe useful to others to calibrate their rigs frequency offset against (with a small bit of math.....)

The antenna is a single horizontal dipole which is aligned more for North/South NZ coverage so it's not presenting is best towards Australia, but hopefully with the added benfit of 20+ dB of algorithm gain with JT4D it will be heard. Wellington doesn't experience many openings due to the top of the south island obstructing the tropo path. If the beacon is heard then it will certainly encourage people in the area to make an effort - at least I certainly will.
Output power is about 6dB higher than previously which several distance stations have already verified.

73,
Wayne

[VK3HZ]

Would it make sense to generate the JT4 so that 144.275 was the nominal frequency - i.e. tune to 144.275 and WSJT DF=0?
Then, if your radio is off frequency, WSJT DF would directly show the frequency error.

Regards,
Dave.