Messages

181

The RF Workbench / Re: 1,5 CW beacon project - Concept questions

« on: June 26, 2014, 0853 UTC »

Hey,

I'm not dead! Nor is the Project.
 I just got the hell busy with RL stuff and that made my interests shift a bit towards other projects.

Anyway. There's progress:
- The Software (for an Attiny25) is almost done
- The HF part is done (see picture)
- The µC board is also almost done

Question: I got a Cystall for 10.240MHz. Suitable? I found no services I might affect nor seems this frequency crowded. I also have 10.110 Mhz Crystalls but I like to forsee from annoying the CW'ers.

I also changed te type of Antenna I'm going to use. I've build a MicroVert for 10.240Mhz. Works fine and solves my problem with long wires.

Best Regards,
~Zazzle

182

The RF Workbench / Re: 1,5 CW beacon project - Concept questions

« on: October 02, 2013, 1317 UTC »

Hi there!

I love your attention to detail, Zazzle!  I have never had much luck figuring things so closely - Mother Nature always shows me my folly of thinking I can figure everything out to the decimal point.  One thing I urge you to do: you said in your first post you can bend your crystal freq +/- 20 KHz.  I would bend as far LOWER of 10 MHz as I could get it.  If you can get down to 9980, that's great.  If not, get as far from 10MHz as you can.  There's several time standard stations around the world operating on 10 MHz and you want to get out from under their interference.  For my thinking, 9995 is just too close.  I think you could find several cheap crystals in the 9-10MHz range that might be an even better way to go.

I'm a perfectionist. Sometimes it's a bless (like in my old job as an engineer) but sometimes it's also a pain because I can't stop thinking (what causes problems when it's about overthinking social stuff). Heh!

Understood. But it makes me a wee bit unhappy because I'd need to re-calculate most parts and I also need to re-wind inductors. AFAIK there are some odd 7.xxx MHz crystals in my xtal box. Or I use some 3...4MHz one along with a frequency doubler. I'll check that. But yes, if nothing works I'll try to tune it away from 10M as far as I can. I just checked frequency charts. 10MHz seems to only go for the US and not Europe. But anyway, interfering with government services is a NoGo.

Edit: "Crystal penning" is going to be my friend :)

Are you using a PWM charge controller or a reflexive (switches on and off at preset battery voltage levels) unit?  Why I ask is because although PWM is more expensive, they tend to better use the available hours of sunlight, leading to a better charge.  From your calcs it looks like you are keeping the charge/discharge rates well below C20, which is good.  Also, you might want to consider a time out feature that would cut off your beacon after 6 hours of on time.  That would be helpful, especially in the winter sun months.

Naa, as simple as possible. I think I have a cheap reflexive charger somehere on the attick (just the board, without chassis). If I can't find it I'll go with the charger circuit attached (just scribbled it down, should work fine). Of course PWM would be the best solution when aiming for the best efficiency. On the other hand, the project should be as cheap as possible (since it's prone to get lost). I decided to kill the energy problem with a 80W module (got a verrrryy cheap one from ebay, one cell has a hot spot. I short circuit that one. The remaining 35 cells should work fine). A PWM charger is about 80+ bucks over here. Too much for the project. The panel was less then 15 bucks, shipping included.

C20 goes only for discharging. Lets say the battery is really drained during a winter day and the next day will be sunny, then it charges with like 3-4A. That's okay since I'm okay with, like, 1Ah missing to full charge due to the fast charging of the first 90%. In case I use my own circuit it won't cut off the charging but goes into "CU (constant voltage) charging mode", what allows the battery to keep charging at a lower current.

About the cut of: I go with a different solution: The µC will monitor the battery voltage and if it drops below 11,5V it'll not start another transmission after tehe running has finished. When the battery is back to 12,5V it starts transmitting again. The battery will wear of when staying not fully charged for a longer time but I'm aiming for broadcast-time, not a as-long-as-possible battery life. I can change the battery once a year if needed. The battery I use isn't a new one anyway.

So far I'll try to keep the costs as low as possible. It will keep me from cursing if the project gets's lost... much. Most time I'd spend on the software and circuit. And that I've on my PC so a second transmitter can be build way faster.

Finally, may God bless you on your planned climb.  I was still climbing tall trees in my early 40s but now that I'm almost 60, I realize I was running on stupidity and dumb luck.  Climbing is for kids... please be careful Zazzle!  We radio nuts need to watch out for each other.  Good luck with your project... 73!

Friends say I have that special grin on my face that tells people I'm up to no good. But well, since I still have one year until I hit the 30 (and start to get officiall old)... lets do this! :)

Yours,
~Zazzle

183

The RF Workbench / Re: 1,5 CW beacon project - Concept questions

« on: October 02, 2013, 1041 UTC »

Hi there, ff!

First of all: thank you for the answer: I was already fearing to go without one

Heh, yes. That, it was quite a bunch of text, and there's more stuff I keep pondering in my head. But pondering leads to nothing, doing stuff does. So here we go. This weekend the Transmitter will, if nothing goes wrong, on air.

I'd  settle on 9.995Mhz. Around here it wasn't in use each time I checked in the evening hours every now and then. Tomorrow I'll spend my day adjusting the oscillator and power stage for the best performance. Friday is assembling day and on Saturday late evening the baby is set free. When it comes to the climbing... luckily I'm quite acrobatic and may also use a climbing harness. Man, I'm so exited. I hope no one will damage or steal it.

I also had some more thoughts about the signal. So far I wanted to send dashes each 10 seconds to get attention. Each 10 Minutes I wanted to transmit the message. But that's stupid. Who's listening to boring dashed for, like, more then 5 minutes? Instead, I decided to do it different.. I send the message all teh time but slow. It has some advantages. Firts, possible audience will know pretty fast that it's a message and will listen to it until the point it starts to repeat. Second, I can send the message more slow, making it easier to read when with a bad SNR. I got to have a close eye on the available charging capacities during dark winter days.

Maybe I won't stick to "space is three times the time of a 'dat'". Hell, since the message is simple I guess everyone can tell the words apart.

Anyway, I got a 12V/7,2Ah battery. It offers enough buffer for really bad days when, for example, it snows a lot. For those interested, here's the way I calculated my signal timing in regard to the energy consumption.


MESSAGE =
XXXXX SOLAR POWERED NIGHT TX ONLY 1WTX UBAT 125
     

TX active time (per message)
----------------------------------
. = 61 (* 1s) =~ 61s
- = 63 (* 3s) =~ 189s
==================================
TX(on) = 250s
==================================


Message duration
----------------------------------
+Sign AND letter spaces (5s each) = 124 (* 5s) = 620s
+ TX(on) = 250s
==================================
Duration = 870s
==================================


Message per hour
----------------------------------
3600s / 870s =~ 4,20
==================================
Messages / h = 4,20
==================================


mAh / h consumption
----------------------------------
(100% / 3600s) * 250s * 4,20 = ~ 30%/h
(240mA/100%) * 30% =  72mAh

+ 16h (winter) * 72mAh = 1152mAh
+ 24h * 5mA (system) = 120mAh
==================================
(Winterday) = 1272mAh
==================================


Worst charge condition
(The case of a snow covered module is ignored)
----------------------------------
Sun radiation in winter = 50w/m2
= 5% from Summer (1000w/m2)

5% from 80W = 4W
I(charge) = 4W/17V = 235mA
Charge hours per winter day = 5
5h * 235mA = 1175mAh
==================================
Charge per winter day = 1175mAh
==================================

184

General Radio Discussion / Who wrote...

« on: September 27, 2013, 1223 UTC »

Hi there!

There's this wonderful article on the wiki. Sadly the contact (mail) below doesn't work anymore.

I want to leave that beautiful and empathic soul of a human being a response

Does anyone has a working contact? It's also okay to tell the person in context to contact me - if that way works better.

Yours,
~Zazzle

185

The RF Workbench / Beacon Project "Common and Precious" (OFF air, 10.237,5kHz, 5W)

« on: September 27, 2013, 1222 UTC »

Hi everyone,

Firts of all: I'm not a native speaker of the english tongue. Please bear with me in case I screw up the grammar every now and then.

I toy with RF stuff since my childhood. (I have a passion for RF stuff on shortwave since I was eight. Back then my grand mother gave me her old valve radio as a birthday present and after I hit the SW button one day in the evening I could not let go. For me, SW is the modern way of the 'travel bug'). I've build quite some stuff so far and operate a small "wide range radio thermometer grid" in my area (µC controlled, solar powered, 1W 70cm transmitters. The farest one is 8km).

Now I want to build a CW beacon. Why? First, there is this a certain curiosity on the technical side: tinkering and the question if someone will pick it up, ever. Then there's this romantic side. A CW beacon is some kind of light house in a dark, stormy night. It's there when no one's around, sending it message to whoever may hear it.

So, enough smalltalk. Lets start with some technical stuff

1) The concept:
The whole beacon will be solar powered (by a 20-40W PV panel - overdone for the summertime but will also offer enough charge during winter) and controlled by an AVR controller. It will charge during day and as soon as the sun has set it'll start transmitting a message. The mikrocontroller will monitor the battery and shut down the device to keep itself in operation with 20% of battery capacity remaining as a buffer. The Battery, charge controller, mikrocontroller and transmitter will be mounted inside a water proof box. It's a low budget project because I guess sooner or later someone will find and steal/disassemble or damage it. The problem is that I live in a rather large city near its limits and so far I couldn't find a proper place that would allow to mount such a transmitter high above the ground without being noticed. Therefore I have to make a tradeoff between performance and security.

Picture

2) Location
The main problem is the place where I live. It's a big city. There are no hills around. But there's lot of destructive people that like to damage stuff and there's a lot of background noise. The surrounding land is more or less flat (and used for agiculture purposes). My focus is on three primary locations:

A) Old Airfield

Picture

It's possible to mount the module close to the ground so it won't be visible from some distance. There's an old fence with massive wooden post running across the field. I could mount long wooden slants to them, holding the transmitter an Antenna.

PRO
- No buildings around
- Wide open space
- If installed clever, not visible from the distance
CONS
- The Antenna will only be 2-3m above the ground
- Easy to reach / disassemble / damage

B) Old bridge

Picture

I could install the PV module and transmitter easily in the middle of the bridge and run the antenna wires left and right towards surrounding trees.

PROS
- Transmitter and module easy to hide
- Not easy to reach
CONS
- The construction is made of steel
- The top of the bride is just 3-4m above the ground since its socket is below the ground level.

C) Old depot house roof

Picture

Except of the (thin) antenna wires the whole setup is easy to hide. Climbing into the roof is hard and requires acrobatic stills. Therefore the setup is not prone to be stolen or suffering from damage.

PROS
- Not easy to access
- Antenan wires will be 10-12m above the ground
CONS
- Still in the city, higer building on one side, an open air field on the other side
- The roof construction is made of steel

3) The frequency.
I'm completely not sure about the frequency I want to use. My circuit is cabable of tuning about -/-20kHz around the fundamental crystal ferquency. I have crystals for:

10.00000 MHz
13.25583 MHz
16.48555 MHz

For me it's important to not disturb the HAM bands or any other service like nautic communication and alike. But of course I want my beacon to be noticed. Therefore I'm looking for a frequency that's not prne to cause trouble but is still likely to be scanned frequently.

My favorite is the 10MHz one. Because it's close to the 30m CW band.

4) The Signal.
This is primary about battery lifetime. Like told before, the whole device runs on Solar power and I also want it to operate during winter, even if not all night long. I have to make a decision between the TX-Time (the more often the more possible the beacon will be noticed) and battery lifetime (there is no use in having the transmitter shut down after just one hour of operation).

At the moment the Concept looks like this:

- Every 10 seconds a 1s long dash (to get attention)
- Each 10 Minutes the following message will be transmitted:

"<LOCATOR> SOLAR NIGHT ONLY UBAT 125" (where UBAT 125 means BATTERY VOLTAGE = 12,5V.)

5) Antenna
I think I go for a classic wire dipole. It will be quite long (23 ft. 4.8 inches / 7.1 mtr. per element) but on the other hand it's easy to build and mount. The box holding the transmitter will be mounted in it's middle. Anything I should pay attention to?

6) Operation times
Given that the signal travels way more far during night I forsee from running the transmitter during day. What's your opinion on that?

7) RF-Power.
Currently the Transmitter delivers 1,6W into Z=50R. Is that too much? Since it's CW I guess it's quite a lot. On the other hand, I have some background noises to overcome, the antenna isn't mounted very high and I still want to bridge some distance.

Yours,
~Zazzle