Doomsday Rig

Everything technical about radio can be discussed here, whether it's transmitting or receiving. Guides, charts, diagrams, etc. are all welcome.
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sinus trouble
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Doomsday Rig

Post by sinus trouble » Mon Jan 29, 2018 12:27 am

Hello Necks! :)
I guess the title seems a bit sinister but we cannot predict what is around the corner!
A transmitter can be a handy piece of kit especially if cell communication networks are out
A CB/Emergency system has proved effective in many disaster situations but is not as common as a Band II FM receiver!

I Have a couple of 5watt exciters to spare so heres my thinking

Lightweight and compact
Rugged and sealed (no fan) Possibly an external heatsink
Lacquer or potting compound for PCB? Not sure?
Mic pre amp for direct voice interface?
Basic power meter? Analogue or LED?

The exciters run from 12v to 15v @ approx. 1amp so could easily be run from salvaged batteries etc
I will add some sketches but if you have any ideas? Please let me know
I am as stupid as I look! :|

regulaterz
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Re: Doomsday Rig

Post by regulaterz » Mon Jan 29, 2018 9:39 am

sounds very good mate looks like your not the only one thinking ahead check this out-SORRY IF IM NOT TO POST LINKS - https://www.copblock.org/171586/norfolk ... ie-attack/

i would say they would go down well in a dooms day shop or what not how much would you sell them for? CB radio is not as popular as the norm fm radio is in almost every car and house even on most smart phones you got a fm radio .may be build for other formats as-well MW SW etc..

Good luck with the project :tup

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Re: Doomsday Rig

Post by yellowbeard » Mon Jan 29, 2018 2:38 pm

Transmitters and aerials have already been set up by National and commercial broadcasters, so a high power three phase generator and plenty of fuel would probably be more useful on the FM band, as well as knowledge of where the transmitter sites are and how to hack in power and audio to them, and it may be more secure. Your home made transmitter would do better into the large antenna arrays already on hills all over the place if a large power source was not available, but it would need to be PLL or crystal controlled for modern receivers to lock onto. Amateur radio has everything you need already for other frequencies, HF radio transceivers have greater range, more available bands and in some cases can be persuaded onto broadcast bands.

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Re: Doomsday Rig

Post by sinus trouble » Mon Jan 29, 2018 11:37 pm

Thank you both for your feedback :)
I find it quite interesting how society copes when faced with dire situations, when the luxuries we have grown to depend on are suddenly taken away!
I believe in the aftermath of hurricane Katrina? Food, medical supplies and shelter became harder to find!
Electricity, phone lines and internet was also wiped out for many
A group of radio enthusiasts assisted the emergency services to reach and rescue the survivors!

Anyways I have done a basic diagram of the Doomsday Rig(TM) :lol:
A steel case would be tough! But heavy and corrosion prone? so id probably go for a pressed aluminium or die cast type?
The exciter already has a LED RF power indicator but is tricky to read? I have a few LM3915 ics which could make a nice bar graph type tuning aid? Or maybe go for a oldskool needle meter?
I am undecided on a MIC pre amp too? I have some LM386 ics that could do the job?
Doomsday Proto.PNG
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Re: Doomsday Rig

Post by OgreVorbis » Tue Jan 30, 2018 12:27 am

I've had this idea before, but it never came to fruition.

It's a good idea because many of the Doomsday type of people buy ham radios like the Baofengs, but they don't think about the fact that the number of people they will be able to reach that way will be really small and that a normal broadcast transmitter would be more useful even if it is not a two-way type of communication.

I also think that it could be an advantage for your transmitter to be able to reach some ham band as well. Maybe you could tune the transmitter to hit the 50MHz or 150MHz ham bands in addition to the FM broadcast.

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Re: Doomsday Rig

Post by Albert H » Tue Jan 30, 2018 1:50 am

Don't think of using an LM386 as a microphone amplifier - it's actually designed to drive a loudspeaker, and is a hissy and distorted little bugger. If you want a simple microphone amplifier, use a quad op-amp like a TL074 (a good choice since it's designed for low noise). Use the first op-amp in the package as a balanced to unbalanced converter (so you can use a good quality dynamic microphone without it humming), use the next couple of op-amps as a basic compressor (with a FET as the variable element), and the final one to provide basic tone control to make the microphone channel sound good with any voice.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Doomsday Rig

Post by Albert H » Tue Jan 30, 2018 1:56 am

You also need to include (in no particular order):

Anti-stupidity protection, so that it can't be operated without an aerial connected

An audio limiter to prevent over-modulation

Reverse polarity protection (a bridge rectifier solves this problem, and if you use Schottky diodes, the voltage drop is only 0.2V)

Silence / audio detection to flash LEDs to show that there's actually something modulating it.

The simplest possible controls - the person operating it may not have ever seen a transmitter before.

A set of simple - probably pictorial - instructions etched into the case


There's so much to do .......!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Doomsday Rig

Post by thewisepranker » Tue Jan 30, 2018 8:58 pm

Albert H wrote:
Tue Jan 30, 2018 1:56 am
Reverse polarity protection (a bridge rectifier solves this problem, and if you use Schottky diodes, the voltage drop is only 0.2V)
If you use a FET, gate resistor and a 15 V Zener (to protect the gate) the voltage drop can be in the low mV...

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Re: Doomsday Rig

Post by sinus trouble » Tue Jan 30, 2018 11:53 pm

Many thanks for all the input :)
I don't know if I gave the wrong impression? But I wont be selling these!
However I do like the compressor/pre amp idea, Also the instructions part!
I do have the PLL DIP settings but on the run may not be so convenient?
I am thinking of making a single control PCB which contains all front panel sections, I have made a start testing a bargraph type indicator for power output! looks good so far!
20180130_232812.png
PS Excuse the workbench! :lol:
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Re: Doomsday Rig

Post by nrgkits.nz » Wed Jan 31, 2018 9:46 am

If you build an SWR bridge, you can use the ADC inputs on a 16F PIC along with an LCD (HD44780) to display forward and reflected power and SWR, calculate the SWR in the PIC code from the fwd/ref power.

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Re: Doomsday Rig

Post by thewisepranker » Wed Jan 31, 2018 1:19 pm

You'd be better off using an LCD display to display current frequency and power output etc. with an auto-dimming backlight if no buttons are pressed within 5 seconds or so. LEDs use quite a lot of power in terms of what is available from a small battery - those 10 LEDs that form the bargraph will empty a good 18650 cell in about ten hours.

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Re: Doomsday Rig

Post by regulaterz » Wed Jan 31, 2018 6:14 pm

like the sl work bench mate :lol:

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Re: Doomsday Rig

Post by sinus trouble » Thu Feb 01, 2018 12:02 am

regulaterz wrote:
Wed Jan 31, 2018 6:14 pm
like the sl work bench mate :lol:
HaHa! Cheers! :lol:
I am as stupid as I look! :|

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Re: Doomsday Rig

Post by sinus trouble » Thu Feb 01, 2018 12:25 am

I Have to agree the bar graph style LEDs are quite hefty on the consumption side which I want to avoid and the LCD would be much efficient!
Just two tiny problems?
1. I am totally shite at writing PIC programs from scratch! :lol:
2. I would like it to be as simple and tough as possible? After all this is Armageddon here! Alien attacks, Meteorite crashes and worst of all!! The British weather!! :lol: :lol:
Bad jokes aside, if anyone has any links for LCD designs? Id be more than willing to learn more!
I am as stupid as I look! :|

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Re: Doomsday Rig

Post by OgreVorbis » Thu Feb 01, 2018 2:30 am

I can program PICs decently if you ever need some help. I use MikroC as my compiler. I don't know what model of PIC chip you are using, but if you want a nice bar graph/control menus on the LCD, you might want to go with a PIC18F series rather than the PIC16F that I see everyone using. The cost of the 18F chips now is about the same as the 16s, so there really is not much of a reason to use them except for old code compatibility. You'll probably run out of space on a 16F pretty quick if you want SWR protection, FWD and REF power display, audio bar-graph, etc. Maybe if you can do it all in assembly from scratch, but that's pretty hard.

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Re: Doomsday Rig

Post by yellowbeard » Thu Feb 01, 2018 7:22 am

If you want simple and rugged, maybe consider a BGY33 amplifier module? One of our Dutch shipmates is flogging used ones for €45 Euro, they need 100 - 150mW drive to do 18-20 Watts out @ 12 Volts and are hard to blow. :smoke

Code: Select all

https://www.amateurradioshop.nl/webshop/modules-rf/detail/523/bgy33-philips-gebruikt-exemplaar.html

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Re: Doomsday Rig

Post by Albert H » Thu Feb 01, 2018 12:14 pm

thewisepranker wrote:
Tue Jan 30, 2018 8:58 pm
Albert H wrote:
Tue Jan 30, 2018 1:56 am
Reverse polarity protection (a bridge rectifier solves this problem, and if you use Schottky diodes, the voltage drop is only 0.2V)
If you use a FET, gate resistor and a 15 V Zener (to protect the gate) the voltage drop can be in the low mV...
True, but connecting it the wrong way 'round just stops it from working. There's also the option of making it work from a low voltage AC source if you use a bridge rectifier. I have (for example) a little water turbine that's good for about 150 Watts and delivers (roughly) 18V AC. Rectified and smoothed, that's going to be fine for a small rig (as long as the water keeps flowing!)
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Doomsday Rig

Post by Albert H » Thu Feb 01, 2018 12:23 pm

OgreVorbis wrote:
Thu Feb 01, 2018 2:30 am
You'll probably run out of space on a 16F pretty quick if you want SWR protection, FWD and REF power display, audio bar-graph, etc.
If you're going to do all that in a PIC, you could also use it to read your DIP switches and dump the I²C data into the PLL chip!

One PLL I did used two little hexadecimal rotary switches using just six PIC pins - two for the commons (switched in software) and four for the switch outputs through diodes. It saved a little bit of space on the board (it was mostly surface mounted parts), and saved me two PIC pins for other functions.

The 18F series of PICs are really cheap and very capable - they're the way to go for new designs.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Doomsday Rig

Post by Albert H » Thu Feb 01, 2018 12:41 pm

yellowbeard wrote:
Thu Feb 01, 2018 7:22 am
If you want simple and rugged, maybe consider a BGY33 amplifier module? One of our Dutch shipmates is flogging used ones for €45 Euro, they need 100 - 150mW drive to do 18-20 Watts out @ 12 Volts and are hard to blow. :smoke

Code: Select all

https://www.amateurradioshop.nl/webshop/modules-rf/detail/523/bgy33-philips-gebruikt-exemplaar.html
I really like the BGY33 / 133.

DO NOT buy the Chinese ones - they're entirely bogus and do not work. A friend of mine needed a couple of these and tried the Chinese jobs. Neither did anything. He popped the top off one of them and found that it was actually some kind of audio amplifier in there!

Years ago, I came up with a simple driver for these, with a BF961 FET oscillator driving a pair of BFR96s to about 190 mW. This went through a bandpass filter (GFWB3) into the BGY33 at about 135mW. The output of the module then went through a conventional 50Ω in, 50Ω out twin-pi-filter. With a 14.4V supply, I got 20 Watts exactly every time, and the worst harmonic (the 2nd) was down around -74dBc. The only minor problem was the heat from the module - it made as much heat as it made RF! A large heatsink solved that one.

These rigs were built into diecast boxes, and there are still loads of them in use all over the world. They're pretty robust. The supply fuse was an FF type at 3.15A. If the match was dreadful, the fuse would blow before the module was damaged. I have one of them here somewhere (in a box of old stuff that needs to be sorted out) and if I can find it, I'll put a couple of photos up here.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Doomsday Rig

Post by s2000 » Fri Feb 02, 2018 9:58 pm

sinus trouble wrote:
Tue Jan 30, 2018 11:53 pm
Many thanks for all the input :)
I don't know if I gave the wrong impression? But I wont be selling these!
However I do like the compressor/pre amp idea, Also the instructions part!
I do have the PLL DIP settings but on the run may not be so convenient?
I am thinking of making a single control PCB which contains all front panel sections, I have made a start testing a bargraph type indicator for power output! looks good so far!

20180130_232812.png

PS Excuse the workbench! :lol:
Just looking at that breadboard, if you want to lower the consumption on the lm3915 circuit just pull the supply voltage off of pin 9, I think this is the "mode select" pin on the IC. It will then run in "dot" mode rather than "bar" and extinguish all but one of the LEDs and still allow you to read the power/swr. I would imagine it would save a fair amount of current from the battery.

I read somewhere once that the Russians still use vacuum valves (to some extent) in all their top military planes as they are much more resistant to EMP strikes than solid state devices! The Americans (apparently) went the other way and use solid state with heavy screening... It would be interesting if anyone knows anymore about this? Might be crucial for the Doomsday Rig :tup

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