lockdown boredom

[Santiago]

bought this little board a while back, saw it on flea bay said 6watts fully assembled and tested.
anyone shed any light on it? looks like a rdvv board but did not come with any paperwork, just this in a box with heatsink., doesn't look like it's got much filtering.

with all the quarantine buisness I'm half tempted to wack it up a tree on a car batt and broadcast some pre recorded sets for the local masses.. got an old pawsey stub in the garage I can use...

[nrgkits.nz]

Also with all the lockdowns around the world, I don’t think authorities are actively enforcing/collecting rigs as much, if at all right now. I suspect they’re only going for the really important stuff, eg interference to the local airport (that’s if they even have any flights), and the average Joe Bloggs who wants to broadcast from his house will get away with it for the time being - that’s until the current situation with Covid19 has moved on. I’m sure guys like Eric Gotts won’t want to risk contracting that, just to seize a rig.

[teckniqs]

I also bought one of those from polestar on eBay and it doesn't work at all, the frequency won't change UP or DOWN and it just stays 'UNLOCKED' and the screen just flashes when you press 'SET' (lock) and it does nothing. I wouldn't be surprised if yours is like it too, complete waste of time, I will stand well clear of buying anything else from this person ever again in the future.

...Thought that 40 quid was a good price until it arrived, complete waste of money!!!

[Santiago]

@neckmin makes sense, very tempted.
@techniqs yea I think that's the same fella I got this one off, Albania or somewhere... it arrived and then I must have slung it straight in the back of the cupboard so I have no clue if it works or not! I'm going to have to try it now..

if it doesn't work no matter, I've got a couple more H rigs I can use but they are much more powerful in comparison... car battery wont last long!!!

[teckniqs]

I think he is from Turkey but it didn't take very long to arrive, only a few days. But no matter what I do it just won't retune using both the buttons on the screen or the buttons on the main PCB.

....A complete pile of shite.

[teckniqs]

Also, be very careful when it comes to using Car Batteries, because when the voltage drops below around 11v and current is still being drawn it will damage them.

[Electronically]

Also, be very careful when it comes to using Car Batteries, because when the voltage drops below around 11v and current is still being drawn it will damage them.

your absolutely right about damaging them. I used a car battery when it drained. the transmitter made a very loud bang.

Sent from my AMN-LX9 using Tapatalk

[Santiago]

any way to get it to shut off when voltage drops off?

I'm going to dig out a 12v psu and dummy load and try this little board out

[teckniqs]

You will need a cutoff circuit, I have seen them on eBay but they seem to just cutoff at 12v but it's ok to go down as far as just below 11v with them.

....A friend of mine makes them for me and they are voltage cutoff adjustable.

[thewisepranker]

There is a way, yes. You'll have to build a circuit to do it. You'll see examples on the Internet using relays but they waste quite a lot of power.

To illustrate just how much power relays waste, your typical cheap relay requires about 5-600 mA to drive the coil. If you're running a 2 A load off a pretty standard 45 Ah car battery, the relay will eat up about 40 minutes of your runtime over a 24 hour period. But that's not the only issue with these common circuits as I'll explain.

The attached schematic will cut off at around 10.8 V with the values shown and will stay off indefinitely. No adjustment is required and standard resistor values can be used. 1% resistors (R7, R8, R9 and R10 only) will put the trigger voltage between 10.64 V and 10.97 V which is a good place to be to get the maximum capacity out of your battery without damaging it. Do not try to go any lower, there's no capacity available there anyway as the discharge curve is falling off a cliff by this point.

It is not the usual window comparator, which is susceptible to turning back on again when the ESR of the battery is effectively zero when the load is disconnected and the voltage allowed to climb. Window circuits require the comparator to be powered all the time, which still presents a load to your battery, so despite fitting a "protection" circuit, you can damage your battery if you forget to go and at least disconnect it within a few days or so.
It is optimised for minimal power consumption, especially once it has triggered. The current consumption once it has triggered and turned off is around 1.2 uA, which is probably a few orders of magnitude less than the self-drain current of the battery.

The FET isn't cheap on the face of it (80p from RS, MOQ 10) but easily cheaper than you can buy a Songle SRD-12VDC-SL-C (an example of a cheap, commonly used Chinese relay from eBay - about £1.50) and the on resistance is about 5 mΩ - insignificant. You could replace the comparator, FET and voltage reference for any alternative that you have laying around or want to fit for whatever reason, but I would advise against using a Zener diode in place of the voltage reference for a number of reasons but this is getting quite long already.

[Santiago]

@wisepranker thank you for taking the time to write that all out and provide diagram, probably ultra simple for someone with your skills but have no tools or time to build anything *you would presume on lockdown I have time but no i have 3 year old twins*
I was hoping there was something on flea bay I could just order and sling up.
also if I use the one of the larger rigs I'll need to step it up to 24v because of the way its wired up which will also loose me time on the battery

[Santiago]

I presume as its is says around 90% efficiency

[teckniqs]

@wisepranker thank you for taking the time to write that all out and provide diagram, probably ultra simple for someone with your skills but have no tools or time to build anything *you would presume on lockdown I have time but no i have 3 year old twins*
I was hoping there was something on flea bay I could just order and sling up.
also if I use the one of the larger rigs I'll need to step it up to 24v because of the way its wired up which will also loose me time on the battery

...It would be much better to just use two batteries, but you would need to turn the power down in the rig, you could just do this by turning down the Bias of the amp if it has a mosfet device either driving it or as the output, otherwise you probably wouldn't get much 'air time'.

[Santiago]

if you have any links to pre built stuff please post

[Santiago]

@wise i never though of turning down the power, not sure if I even can... I'll try find a pic of one of the boxes

[surefm]

Yes I got one off these from E bay, I had trouble with the locking off and retuning till I unplugged the digital display, seems to work but can't get audio in without a terrible humming noise. being transmitted.

[surefm]

Here a pic

[teckniqs]

Yes I got one off these from E bay, I had trouble with the locking off and retuning till I unplugged the digital display, seems to work but can't get audio in without a terrible humming noise. being transmitted.

What are you using as an audio source? It sounds like your aerial is either too close to it and it's picking up the RF or you might have a bad SWR.

....A lot of mixers are prone to this happening with band one/two aerials near them.

[Santiago]

so works a little better without the screen, I'll try that

[Santiago]

anyone else with some expert input, would be much appreciated