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Messages - Zazzle

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166
Hi everyone,

So, as a HF addict I need my next drug shoot aka "HF project" :). It's going to be a beacon again.

I felt for doing some urban exploring lately which made me visit an old industrial complex not that far away from home. The are several smaller towers on the areal and two big chimneys. I did some climbing. WOA! That would be the perfect location for a Beacon Transmitter. I mean... 80m above the ground and no big city close by. F#ck, yes!

The smaller towers are easy to climb on. The plattform offers many option for installing Antennas. The tower itself is about 50 meters
The chimney is... a challenge to climb on. Exhausting. Getting stuff up there is even more of a challenge. But, my god, what an awesome place for a Beacon. Sadly, there's a metal tube comming from the chimney which is even longer than the platform and may interfer with possible Antennas. Also, it's too risky I think.

So, for reasons of security, accessibility for maintenance and an obstacle free Antenna environment I will go for the smaller tower. The only bad side is: other people might be tempted to climb on it. Less than on the chimney.

I need your opinions now, because I've a hard time making a decision. It's about possible signal propagation and use of Antennas.

Frequency 1 - 10M Band
Pros
  • I have an old 5/8λ CB beam at home. It's easy to install and it's also relatively broadbanded. Therefore, the SWR should be not an issue.
  • I could also use a 1/2λ inverted V. Each side would be about 2,60m. That's managable.
Cons
  • The propagation isn't the best and DX connections are rare.
  • There's not really much activity when it comes to pirate radio/beacons.

Frequency 2 - 40M Band
Pros
  • Awesome propagaion, also during daytime.
  • Many pirate activities just below the offical HAM-Bands
Cons
  • A huge antenna is needed. A Dipole is not an option.  I think I could build a KGD. But this sort of antenna has a very small bandwith and the SWR matching is tricy because it's sensitive to the objects around.

I think a good working Antenna in combination with less potential contacts is still better than a bad Antenna with more possible contacts?

Your opinion? :)

Greetings,
~Zazzle

167
The RF Workbench / Re: Output Filter Issue?
« on: April 20, 2015, 0742 UTC »
Hey redhat,

Keep in mind too that the online calculators for filter design rely on ideal component values.

Jep. :) The C's I've caculated (the old school way with formulas from books and with a cualtaor) ended up with C-values way off from the standard values. But well, paralleling and adding a variable C helped here. I verified my values by using online calcs. Teh values are about the same. +/+ some percent. So I think I got that right.

Sadly, I don't call such equipment my own. :)

Greetings,
~Zazzle

168
The RF Workbench / Re: Output Filter Issue?
« on: April 20, 2015, 0730 UTC »
Hi ff!

Admittedly my understanding of filters is limited, but to my knowledge, if yours is configured for 50 ohm input - 50 ohm output, any large variation from those ideal values will distort the filter's passband - the filter won't be blocking what you want it to block.  I don't recall the specifics of your project but if your PA is developing about 4 watts and the stage is powered from a 12 volt supply, its output impedance is approximately 18 ohms - a long ways from 50.  An easy match at those power levels can be made with an impedance transformer.   If those stated figures are correct, a 6 turn primary (PA side) and a 10 turn secondary (filter side) on an FT50-43 toroid should give a decent match. 

Nono, like written, the lowpass ALSO takes care about the impedance matching. It's possible to combine both. There isn't much to match anyway. I'm aiming for 1,5W, which means an PA impedance of approx 52R.

(VCC+Uce)² / 2xPo

(13+0,5)² / 2x1,5 = 52,083R

The 4 Watts was what I was able to obtain into a perfect load with a lot of tweeking (just for testing. I went back to ~1,5W)

Maybe I should loop in a 1:1 transformer before the filter. Just to see whether anything changes

You probably won't want to do this - BUT - if I were doing it, I would remove the existing filter and build a completely new one, AFTER getting a decent match.  If your twaddling is anything like mine, by now the existing filter is completely at sea, and rebuilding it will be the easiest course of action.

Well, I've build flters before, primary for the 2m Band. That worked well all teh time and that's why I don't get the problem with this thing. I don't know whether the filter is the problem at all. Maybe it's something else. Or a mix. Maybe I should dump this whole concept and start angew from scratch with a completely new circuit whan I'm back from my vacation.

Thanks :)
~Zazzle

169
The RF Workbench / Re: Output Filter Issue?
« on: April 19, 2015, 2138 UTC »
Oh, forgot to attach a picture of the new Filter. Don't ask. Soldered too many times on the board. :)


170
Equipment / Re: Antennas for Beacons (tricky terrain)
« on: April 19, 2015, 2107 UTC »
Hi again,

After having a lot of further frustration with this project, I decided to put it aside for some weeks. Sometimes a little distance helps to obtain good ideas and having a look at the issue from another perspective.

So, what did I do?
  • I checked the wire length of the Dipole. Yep, it was approx 1,5m too long on each side. I corrected that but the received signal strength didn't improve (at my home)
  • That made try it with a BalUn. After testing several impedances, I eventually settled on a 1:2 BalUn (50R:100R). Which gave me the best SWR of about 1.4 in my backyard (with the Antenna about 2m above the ground).
  • I put the Antenna on the industrial roof again and even higher this time. About 3,5m above the roof. Sadly, no big change. The SWR read 1.2, which is fine.
  • Sigh! I took the whole setup back home and installed it on my own roof. Which is 8m above the ground and aditional 2m for the pole where the transmitter is installed on. Again.... no big change. What a frustration! The signal strength behaves like on the industrial roof and I have a hard time picking it up beyond 1000m around the transmitter.

What I'll do next:
  • Testing the Transmitter with a different Antenna. I have an old unused CB Antenna flying around and I'll try to match it with a Antenna Tuner
  • Actually, I start to believe that the Antenna isn't the problem but maybe the filter. (I started a diffent topic about it.) I mean... it delivers ~2W into a 50R dummy load but maybe isn't able to deliver it into the Antenna... problems with reactive load... or what ever. No clue.
  • I'll take the Setup along on a vacation (mountains). Maybe the setup behaves different outside of the city. I doubt it but time will tell.

So, and other suggestions for possible problems? :)

Greetings,
~Zazzle

Oh, I also painted the pole. That was a good suggestion. Blends in with the background way better. Thanks. :)





171
The RF Workbench / Output Filter Issue?
« on: April 19, 2015, 2054 UTC »
Hey,

Jep, it's about the Morse Beacon project. I like to discuss this issue in a different Topic an hope that's okay. If no, please merge the thread with the Beacon topic. :)

I wonder whether I might face some problems with the Output Filter. It's a 5-Pole PI-Filter. A Low-Pas (cut-off is 11,5Mhz) that also manages the impedance matching between PA Transistor an Output (which is 50R).

I'd build the Filter by using some basics formula and a lookup-table (for the impedance transformation). The Filter didn't work (almost no output signal) well and I started modifying values. The PA stage had been calculated for approx 1,5W. After some modification of the component values I was soon able to obtain 1,8W. I tested other values and eventually made it to about 4W with the PA becomming quite hot. Still, the signal looked fine on the Oscilloscope.

But I became sceptical about the 4W and looped a Antenna Tuner in between Transmitter and Dummy. The signal became heavily distorted after introducing just the slightest amount of reactive load (C and L). I undid the latest modifcations and the filter was now able to withstand reactive loads to a certain degree before the signal became distorted again.

I ran a test with my HAM Transceiver. At a certain point it also started to show a distorted signal when too much reactive load was introduced.

My basic question is: how must a output filter respond to mismatching? I attached some screenshots from the Beacon Transmitter output in different situations.

I wonder whether the Filtert causes problems and doesn't feed the Antenna properly... which would be odd, because the SWR Meter says: 1,5W forward, 0,3W reflected.

Thanks and Greetings,
~Zazzle

172
Equipment / Re: Antennas for Beacons (tricky terrain)
« on: March 08, 2015, 2351 UTC »
Hi there Antennae!

First of all: sorry for the late reply. Especially after my previous comment. That's a bit embarrassing. :)

And, thank you for your elaborated answer. I should have said that I'm not completely new to Antenna theory. The issue is that I lack of practical experiences for Antennas in frequencies that low in the current situation. I've been active on UHF/VHF before. Also, I've read that the real thing behaves sometimes completely different from the theory. That's whay I asked. I.e. I read a lot in "Rothammels Antennenbuch". With may be the European equivalent to the ARRL Antenna Book.

Antenna-Type: I'll try a different Antennas during the next days. The German word is "Fuchskreis". No idea what the proper english Term is. See attachment. It's a single pole, voltage feed (high impedance) Antenna that's feed from a parallel resonant circuit. The key feature is the tunable circuit which allows good matching. Also, according to the Antenna book, the impedance stays around 2500R in a wide range of applications and situations. That may help.

But to get behind the issue - whether I have a Impedance matching or location problem - I'll separate Transmitter and Antenna in Future which will allow mw to loop a SWR/Wattmeter into the line for reading.

I asked about the Antenna height because there's a chart for the regular Dipole which shows that the impedance near ground (in regard to a certrain fraction of the wave length) drops around 50R. But yeah... quite possible that the metal construction interfers with the field pretty bad.

(Btw: about the setup at home: NRD-525 / FT897D / PSR-225 / 40m Dipole with Balun and tuner / End-point feed dipole with tuner. So I guess it must be an issue on the TX side)

Sadly, I haven't much options for other locations. The old industry yard is the best suitable so far. But maybe I can have the Antenna run into a different direction - away from the roof construction without it being too visible. I'll just try that in case the Fuchskreis doesn't help. Thank you. :)

About impedance matching: I use a 5-Pole PI-Filter for impedance matching (PA-Transistor and output) and harmonics supression. It matches the output impedance to 50R. I asked about the BalUn becuse I read that Dipole Antennas like to be feed with a symmetric signal. And the output of my Transmitter isn't. But yeah. All theory ends when the Antenna joins the game. Anyway, as soon as I'm able to loop a meter in I'll know more about how it behaves in reality.

Thank you for the time and advise. I hope it'll improve the project. And I keep you tuned. :)

Kind regards,
~Zazzle

173
The RF Workbench / Re: 1,5 CW Beacon Project - On Air Now
« on: March 08, 2015, 2311 UTC »
Good evening!

It's been a while. Projects at work. And not to mention that spring's here. The garden wants attention as well. Anyway. Time for some updates!

I've been on the roof today night and disassembled the Transmitter. That was fun. Obviously, people have been up on the roof. There was a chair (which hasn't been there before) and a - believe it or not - big Dart disk. Funny thing. People have been playing Dart up there. That's why I love this city. Silly people over and over. On the other hand those people have shown no interest in damaging the Transmitter/Antenna/etc. Which I'm grateful for. Psysically and function-wise the Transmitter survived the first weeks of operation. Good!

There are some things on the list that I want to try out on the workbench and in my backyard. The latter regards possible Antenna options and a better impedance matching.

  • I ponder to change the frequency to somwhat around 6.950-6.980Mhz.
  • I'll redo the 5-Pole PI-Impedance matching and harmonics Filter completely. The goal is to add vari-caps which will allow me to adjust the output impedance of the filter without the need to disassemble the whole thing.
  • The fixed antenna gets removed. The Transmitter and Antenna will be seperated from each other instead in future (BNC connectors). That will allow me to loop a SWR/Power-Meter into the Antenna line and read the value on the roof. I really want to know whether it's an impedance matching or location problem.
  • Additionally, I'll try another type of Antenna. The German name is "Fuchskreis". I have no idea what the correct english term in is. It's basically a  λ/2 single pole Antenna without ground that's feed from a parallel resonant circuit. The key feature is the easily tuneable circuit.

Stay tuned. :)
~Zazzle

174
Equipment / Re: Antennas for Beacons (tricky terrain)
« on: February 17, 2015, 1534 UTC »
*chuckles* Well, looks like I have to find the answers to my questions on my own. I'll let you know about the outcome. :)

175
The RF Workbench / Re: 1,5 CW Beacon Project - On Air Now
« on: February 17, 2015, 1103 UTC »
Morning!

So, I finally had a look at the Antenna last weekend. Indeed, I had cut the Dipoles way too long. Approx 9m instead of 6,85. No idea how that happened. The signal increased (especially in quality) after cuting both wires down. I also changes the support wires to Nylon.

Still, I'm not satisfied with the field. The next thing I'll try is a 1:1 BalUn. Feeding the Dipole with a balanced Signal may help.

Greetings,
Zazzle

176
Equipment / Antennas for Beacons (tricky terrain)
« on: February 12, 2015, 1442 UTC »
Hi everyone!

I have two primary issues that I'd like to address. One regards an actual problem and the second is a theoretical one for an upcomming project.

Actual Problem:
It regards this project.
I put a 1,5W Beacon up on a roof. 10.240MHz. It looks like it doesn't radiate the field properly. Maybe the issue clears itself on it's own today evening when I check the correct lengths for the Dipole. I may have cut 'em too long. But I also suspect other issues with the location in general as well. As you can see on the attached photos, the Transmitter is installed on a roof with lots of metal constructions around. Given the low Frequency I suspect the construction to interfer with my antenna. Actually, my questions are:

  • How much may the roof construction interfer with my antenna?
  • I suspect that "as high as possible" is the key for the antenna? I also read that a height of 1x wavelenght is perfect for Dipoles?
  • Does an Inverted V, say, with a 90° angle help here?
  • The Dipoles are constructed as follows: Dipole wire - 1m of Nylon wire as insulator - (conductive) wire/cable until mountpoint on the ground. Should I use a Nylon wire for the entire length for the support?
  • I live in a really, really big city but close to the city limits. How much may the city and it's interferences interfer with my signal?
  • Should I connect the GROUND from my circuit to the roof construction?


Theoretical issue:
I'm going to build a second Beacon. Around 7MHz this time. I like to install it on an old air field.
Some fact on the air field:
  • No building around for at least 300m.
  • The ground exist of sand and ist mostly dry during summer.
  • Little vegetation. A bit of grass and some random trees.

I think it's save to erect a wooden slat of about 4m as the center support for an Inverted V without no one taking notice of it from far away.

So, my questions are:
  • Is there an Antenna type you'd suggest? I'd go for an Inverted V, even if the angle is kinda low.
  • Maybe a "KGD" or a Micro Vert works better?
  • Does it make sense at all? Is a high mounting point for the Antenna the key and I can spare myself the effort anyway?

Kind regards,
~Zazzle

177
The RF Workbench / Re: 1,5 CW Beacon Project - On Air Now
« on: February 12, 2015, 1353 UTC »
Finally, photos of the setup.

Sunday. Installation. First problems:
The signal strength around on the receiver side drops to S1 within ~300m. (Icom IC-90, Set ti AM, Narrow). At home,~5km air line, I got a S1 signal with my NRD-525 and a large wire dipole (in the garden) as well.

Wednesday. Checking for problems. Changing the position.
I went on the roof again and mounted the transmitter on a 3 meter long wooden slat The antenna is now installed as a "wannabe Inverted V". The angle is quite low.

The Signal got better. S3 300 meters away and S2 at home. I also noticed that I may have cut the Dipole wires too long while preparing everything at home. I've calculated 6,85 meters per side. It looks like I accidently cut them to 7.9m or maybe even 8.9m. Since I had no folding rule along... a check is on my list for today. But it would explain the low emission. Feeding point mismatch. I may also add another meter to the wooden slant.

The voltage at the output measures around 8,5Vrms into a 50R Dummy Load, which equals approx 1,5W HF.

Geeky me. I also took a handheld DSO along yesterday. The signal on the Transmitter output looks fine while it's working. Clear sinewave. Voltage stays around ~8Vrms

But I'll open another thread on the antenna issue since I have more question on that topic.

Greetings,
Zazzle

178
The RF Workbench / Re: 1,5 CW Beacon Project - On Air Now
« on: February 12, 2015, 1312 UTC »
Murphy is not my friend! After having it running with a dummy load for days (in the fridge and in the stove to check how it behaves with different ambient temperatures) it suddenly started to run postal and oscillate like mad after adding a shield. But some blocking capacitors and lowering the amplification of the oscillator stage solved the issue. I now have a small intermodulation because of stray capacitance but the double PI-Lowpass takes care of that. An FFT analysis shows: harmonics are within the limits and the output looks fine.

179
The RF Workbench / Re: 1,5 CW Beacon Project - On Air Now
« on: February 12, 2015, 1306 UTC »
Hey everyone!

ah, f# this. I finally got this project done. :)

Of course. I wanted it Solar powered. I wanted it to not only transmit the Locator but also the Battery Voltage and Temperature. And it should include a good charge controller and a low-battery protection function and so on. In the end I got frustrated because it always felt like spending too much work on a project that gets liekly stolen/damaged anyway. Also, after observing the mount of sun (and therefore energy available during winter during the last monts) I came to the conclusion: even a 240W Module would not provide enough energy during winter to have the transmitter operating during night under every conditions.

I reminded myself of a simple but remarkable quote from the movie Contact. Ted Arroway: "Small moves, Ellie, small moves."

So I started programming the AVR controller doing just one thing: providing the key-ing signal. I got my motivation back after that and spend my last Saturday getting everything ready.

I forsaw from using a Solar powered system (but I have plans for a new one. 7MHz this time. Solar powered. But I'll disassemble it during winter so it works fine with a 20W module during Summer. Small enough to hide it).

My location of choice is now an old industrial ruin around the corner. I know every corner of it and it's close by. Perfect. AND there's grid power available from a pumping station that decontaminates the groundwater. The cables run all across the areal.

So, it's on air since Sunday afternoon. It broadcasts: "<LOCATOR> LIFE IS COMMON LIFE IS PRECIOUS <LOCATOR> 1W TX ALL DAY LONG" [RETURN]

The Frequency is 10.240MHz (okay, 10.238,5MHz exactly)

So I called this station "Common and Precious #1". Now, let me spam this thread a bit so I can post more pictures :)

The pictures show the transmitter in its weather proof housing.
  • The PSU (cracked open wall plug PSU. Modified from 12V to 14V.
  • The Attiny25 based Key-ing unit.
  • And the Transmitter with Oscillator- and PA-Stage.


Greetings,
Zazzle

180
The RF Workbench / Re: 1,5 CW beacon project - Concept questions
« on: June 26, 2014, 0945 UTC »
Hey,

I got a question. With about 1W TX-Power I have to keep an eye on my Battery balance, especially during winter. I aim for long operation hours, therefore I have to make a trade-off between the following parameters:

- Length of signs: the longer the sign the more power is consumed.
- Space between signs: the longer the space the more likely that the Beacon gets overheard.
I can't stick to the usual ratio of 1:3 between DIT and DAT because the power consumption would be the same, regardless of long or short signal duration.

So I need your opinion on the following timing:

DIT = 0,7s = 5
DAT = 2,1s = 15
SIGNSPACE = 5s = 50
WORDSPACE = 10s = 100

My timer allows 100ms steps.

What's your opinion?

With best regards,
Zazzle

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