Tuesday, November 01, 2011

Sporadically active on 10m

OK - Ive slug up a very rough horizontal zepp for 10m  - main lobes roughly E/W from here.

Freq currently is 28.000810 MHz - ie tune to 28.0MHz USB  it will be a 810Hz tone

Currently 12wpm call in CW - followed by 10x callsign in QRSS6 FSK

and the results are in...

Well.... 3 hours of ten minutely data gathering done.


Results are.... interesting!


First the graphs:


















And now the raw data:


time ambient C xtal C diff C 10 min change C freq Hz relative drift over 10mins total drift from power-on
09:30 23.4 27.6 4.2
0 0
09:40 23.8 28.2 4.4 0.2 727 0
09:50 23.9 29.8 5.9 1.5 737 10 10
10:00 23.9 31.1 7.2 1.3 754 17 27
10:10 24 32.1 8.1 0.9 761 7 34
10:20 23.9 33.1 9.2 1.1 771 10 44
10:30 24 33.8 9.8 0.6 777 6 50
10:40 24 34.4 10.4 0.6 784 7 57
10:50 23.7 35 11.3 0.9 790 6 63
11:00 23.6 35.3 11.7 0.4 793 3 66
11:10 23.5 35.8 12.3 0.6 797 4 70
11:20 23.4 36 12.6 0.3 801 4 74
11:30 23.4 36.2 12.8 0.2 802 1 75
11:40 23.3 36.3 13 0.2 804 2 77
11:50 23.3 36.5 13.2 0.2 807 3 80
12:00 23.3 36.6 13.3 0.1 808 1 81
12:10 23.3 36.7 13.4 0.1 810 2 83
12:20 23.3 36.8 13.5 0.1 810 0 83
12:30 23.3 36.8 13.5 0.0 810 0 83



So...

After 3 hours the temp seems to have stabilised out as does the freq, and the temp is lower than in previous tests.

Its still however showing better part of 100Hz drift over 3 hours from power on until it settles down.

Thats fine if you are going to be leaving the beacon running for days at a time, but if you are going to be turning on and off for  a few hours at a time thats going to get somewhat annoying. It also means that during warm up you could potentially end up crashing into someone elses signal.

Based on this, as I was discussing with G0CER yesterday, I think the trick here is NOT to switch off the beacon. (Duh!)   Yes I realise the licensing implications here, what I suggest is leaving it running 24:7, but when not present in the QTH to switch the output into a dummy load - that way no (in theory!) RF radiates beyond the boundary of the property whilst the beacon is unattended.


Im also now looking at active cooling - ie popping a heatsink onto the lid of the box and then running some PWM proportional to the temp into a fan to try and hold the temp at a lower constant temp - though as others have commented on the GQRP list - it would be better to address the electronic design first with negative co-efficient caps etc.


I think Ive gone about as far as Im going to go for now with thermal tests. The bottom end of 10m isnt exactly crowded with QRSS sigs, so I guess I can afford to let it wander a bit for now.

Next priority is actually getting a signal out - so Im just cutting a very hurried 10m Zepp to sling out for now. It will be horizontal pola and be strung up roughly north south. Expected main lobes should (fingers crossed!) be heading in roughly the right directions.


More later.
.


Xtal insulation

Polystyrene added around the xtal. This is of course an imperfect solution as the thermo-couple is in contact with the diecast box and will thus be not only reading the case temp but will be radiating some of that heat inside the polystyrene cube.






Tests underway now with this mod and bead jacket between inner and outer box. Ons at 10 min intervals.

Graphs and stats later.


28MHz QRSS beacon - further tests

Sadly no time last night for anything particularly scientific, but having observed temperatures  about a dozen times last night and again this morning it looks like this:


Condx  = 7.3v supply, in diecast box, in outer box, NO beads, sitting on rack.

probe temp holds at around 7C higher than ambient temp.

As the room temp in here varies between 23 - 26C depending on if lights and monitors are on - the resulting swing on the after an hour or so from power on is 30.4 - 33.8 (from observation).

Heating appears to be significantly less than with a 12v supply.

What I plan to do now is:

a) cut a polystyrene block to fit around the xtal inside the diecast box to reduce temperature changes inside the box from any convection etc

b) re-add the beads to provide thermal insulation from room changes.





.....   Oh... and try and get a wire antenna up today :)