About to purchase new 30W!

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chuckens
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About to purchase new 30W!

Post by chuckens » Wed May 29, 2019 2:48 pm

Hi.
So I found this transmitter on Ebay https://www.ebay.co.uk/itm/252473359054 ... Track=true

One of the reviews quotes "Make sure you choose a GOOD clean supply @ 12V -13v 8A you will also need a 20,000 ufd Cap on the supply line If you want your sound to be fat with lots of bass"

I have my eye on a "JETFON 13.8V 10 AMP PSU POWER SUPPLY" Would this be ok to use?

What does he mean by "20,000 ufd Cap" ? How would I hook that up?

If anyone can help me out!!

Cheers

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Re: About to purchase new 30W!

Post by thewisepranker » Wed May 29, 2019 4:30 pm

What is meant by a "20,000 ufd Cap" is a 20,000 uF capacitor. uF stands for "micro Farads".
A 20,000 uF capacitor is huge. The inrush current will probably blow up your power supply if you're using a switch-mode type. It also has nothing to do with bass reproduction, that's not even how it works. Ignore this advice.
If you buy a decent switch-mode power supply, it will have enough output capacitance designed in.

It's not easy to say whether that Jetfon power supply would be any good until you buy one, take it apart and have a look at the design (assuming you know what you're looking for in a power supply). Then try it and the rig on the mains and stick the whole lot on a spectrum analyser. And if you do, set it up better than they do in the listing! The way they've configured the spectrum analyser is a common trick to make something look fairly clean.

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Re: About to purchase new 30W!

Post by McDonalds » Wed May 29, 2019 7:54 pm

defo get one of these makes signal much better
https://www.superyagi.com/FM_88_to_108_ ... 78057.aspx

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Re: About to purchase new 30W!

Post by Albert H » Fri May 31, 2019 4:05 am

Please don't buy one of these sprog boxes. It may deliver "30 Watts" but they will be strewn around on many frequencies!

These stupid Chinese interference generators use the "stereo broadcaster" chips meant for micropower use to allow you to play a portable CD player or an MP3 player into your car radio. The ICs that are designed for this purpose are NOT meant to be amplified. They are inherently dirty, and the broadband nature of the power amplifier in these Chinese efforts means that all the unwanted spurious outputs are amplified too.

If you use one of these, you will receive an "unfriendly visit" very quickly, as it is almost certain to cause interference to other broadcast stations in the vicinity and to other services.

One of these things caused massive interference to a local taxi repeater, so the taxi company owner located the operator of the Chinese spur generator, and visited him explaining the problem and asking (apparently in a friendly manner) if the guy could either stop using it or get it fixed so it didn't cause interference. The owner of the Chinese rig stopped using it for a day or two, and then fired it up again the following weekend, damaging the taxi company's business over a holiday weekend. The owner of the sprog box was warned again to stop (in a less friendly manner), but it was soon back on the air. A day or two later, he received a visit from some motorcycle-riding pals of the taxi company owner. The rig was removed and destroyed, and the pirate operator is finding it really difficult to walk properly these days....

If you want to broadcast - even at relatively low power - do it properly. You won't have the necessary equipment to test a transmitter properly, to make sure that it only generates the frequency that it's meant to. Get one competently built by someone from this site - it'll cost you much more than the Chinese interference generator, but might just save your legs......!
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"Because it doesn't know the words!"
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Re: About to purchase new 30W!

Post by teckniqs » Sat Jun 01, 2019 9:57 am

Those cheap Chinese transmitters are surprisingly very clean for what they are, I know someone who has tested one into an analyser on various frequencies and the harmonics/etc were all at a safe level.

As much as I wouldn't ever bother with one myself and only use proper gear, if you need something cheap and you're not serious about Broacasting then they aren't as bad as the usual stuff that comes out of China described above.

But don't quote me on this, I'm not for one moment saying they are all clean and safe because I've only seen the results of ONE of these.

I would be very interested to see the output of the 150w version though...

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Re: About to purchase new 30W!

Post by nrgkits.nz » Sat Jun 01, 2019 12:49 pm

Ok here’s one I had on my bench a while back
5A1732BD-A6FE-4ABD-ACDF-4A49BDEDD42C.jpeg
Look at all the in band spurs
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Re: About to purchase new 30W!

Post by teckniqs » Sat Jun 01, 2019 1:09 pm

nrgkits.nz wrote:
Sat Jun 01, 2019 12:49 pm
Ok here’s one I had on my bench a while back

Look at all the in band spurs
They are very clear to see, but it's also very clear to see that's a completely different Chinese transmitter....

In the past I've seen a similar one to yours with absolutely NO low pass filtering and the RF was straight out from the output device to the antenna socket.

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Re: About to purchase new 30W!

Post by thewisepranker » Sat Jun 01, 2019 11:44 pm

nrgkits.nz wrote:
Sat Jun 01, 2019 12:49 pm
Ok here’s one I had on my bench a while back

5A1732BD-A6FE-4ABD-ACDF-4A49BDEDD42C.jpeg

Look at all the in band spurs
-50 dBc is 5/7ths of the way to being ITU compliant!

I can't believe that it's doing what looks to be exactly +30 dBm... It's blurry so could be 30.08 or 30.80 for example.
You must have a reference level offset because those analysers can only handle +20 dBm but why such an offset to make it exactly +30?

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Re: About to purchase new 30W!

Post by Albert H » Sun Jun 02, 2019 12:24 am

A friend of mine needed a bunch of 10 Watt rigs, so got a supplier in Hong Kong to ship him a selection of Chinese boxes that could do that power. All of them were comprehensively tested, and all of them failed even the most rudimentary tests. It was significantly cheaper to have some PCBs etched, and build something similar to the Dutch RDVV exciters, using a 15 Watt Mitsubishi FET for the final. Of course the European rigs were really clean and consistent. We also had cases and internal screens made, and these turned out to be very neat, cheap, simple exciters with really pure output, and no conducted RF problems (unlike the Chinese rubbish).

Do yourself a favour and get a proper rig!
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"Because it doesn't know the words!"
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Re: About to purchase new 30W!

Post by chuckens » Mon Jun 03, 2019 2:50 pm

Thanks, everyone for your input. I already have one of these https://www.ebay.ie/itm/163109003546 7Watt but I just wanted a bit more power. What do you suggest then?

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Re: About to purchase new 30W!

Post by yellowbeard » Mon Jun 03, 2019 8:31 pm

chuckens wrote:
Mon Jun 03, 2019 2:50 pm
Thanks, everyone for your input. I already have one of these https://www.ebay.ie/itm/163109003546 7Watt but I just wanted a bit more power. What do you suggest then?
In good faith I cannot tell you to add an amplifier to that type of transmitter. If its output is like the one posted by nrgkits.nz, then you will cause a lot more interference to stations in the band and probably outside the band too. I am being polite. The other users here are going to tell you "planes will fall" and "£1,000 fine or a months hard labour". It's a dirty yoke, it was designed for cheap mass production with readily available parts and it has a bad reputation. You could clean it up by butchering it and replacing the PLL/stereo encoder/oscillator and just using the amplifier, that's the scale of the problem. I am still being polite - honest!
Image

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Re: About to purchase new 30W!

Post by nrgkits.nz » Tue Jun 04, 2019 2:14 am

thewisepranker wrote:
Sat Jun 01, 2019 11:44 pm
nrgkits.nz wrote:
Sat Jun 01, 2019 12:49 pm
Ok here’s one I had on my bench a while back

5A1732BD-A6FE-4ABD-ACDF-4A49BDEDD42C.jpeg

Look at all the in band spurs
-50 dBc is 5/7ths of the way to being ITU compliant!

I can't believe that it's doing what looks to be exactly +30 dBm... It's blurry so could be 30.08 or 30.80 for example.
You must have a reference level offset because those analysers can only handle +20 dBm but why such an offset to make it exactly +30?
It wasn’t exactly 30dBm, it was around 30.8 from memory or there abouts. This was a “1watt” Chinese exciter brought in by a customer of mine because it got him in trouble, the span on the analyser was also about 3MHz. I use a 30dB power attenuator for all low power stuff into the analyser and just set the offset to compensate - the analyser readout for power is accurate to about +/-1 dB however for much better accuracy I have a bird wattmeter as you can also see in that photo. I also have a bird coupler (not in that photo) which I use for coupling in PA’s for measuring harmonics etc... anything above 10watts goes into the coupler then into a 50ohm load sitting under the bench which will handle high power.

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Re: About to purchase new 30W!

Post by GotDaKnowledge » Tue Jun 04, 2019 9:40 am

Nice video on this 'transmitter' -

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Re: About to purchase new 30W!

Post by nrgkits.nz » Tue Jun 04, 2019 10:25 pm

Those all in one fm chips are quite noisy - you can see all the inband rubbish and raised noise floor around the carrier, as Albert said they’re not designed for broadcast use. If you were to replace the all in one chip on the board in that video with a conventional colpitts or Hartley oscillator driven by a pair of varicaps and a pll chip then the result would be a very clean carrier with good phase noise. The phase noise measured at 10Khz from center frequency on my NRG Pro 5 design is -110dBc/Hz or thereabouts and it’s power output is variable from zero to 6watts while staying absolutely clean. https://www.nrgkits.co.nz/index.php/pro ... ansmitter/

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Re: About to purchase new 30W!

Post by radionortheast » Wed Jun 05, 2019 9:46 am

you might be aswell to try these 30w transmitters, even thought I don't like the inbuilt stereo encoder rubish, my 8015 pcs transmitter has gone rogue and started transmitting on other frequencies lately. :)

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Re: About to purchase new 30W!

Post by SamTheDog » Mon Aug 05, 2019 10:06 am

Most of the far-eastern transmitters are intended for the home-hobby market and definately not for any serious broadcaster.
some use ba1404 and bh1418 type single-chip rf parts. With not much more than a few stages of amplification, and if you're very lucky a crude o/p filter.. These rigs are seriously crap!. the makers seem to spend more time on the pretty display and nice box rather than decent circuit design and efficient filtering.

There are some superb exciters available if you are willing to pay for them... but generally NOT from china / far-east.

In the past I have bought gear from FRB. in Berkeley california. and they are OK. ALSO. sometimes good commercial exciters
turn-up fairly cheaply. I recently bought a 30-watt CTE exciter for just over 200UKP. (see page below...).

It can be tricky sometimes to justify a few hundred for a transmitter that you will then leave in a lift motor room or on a hilltop somewhere.. BUT if you use a cheapo sprog-box it will be pounced-on by the authorities sooner rather than later.

http://www.qq22.net/playground/page/y.html
Sam The Dog.....

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And many moons ago.. WNKR on FM and Shortwave.
info@torradio org / qq22.net / TorRadio.ORG

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Re: About to purchase new 30W!

Post by nrgkits.nz » Mon Aug 05, 2019 11:43 am

If you’re after a good quality transmitter that will do kilowatts and money is not an issue, then my recommendation is either Nautel or Eddystone-Broadcast - they supply all the commercial markets in lots of different countries. Eddystone is even in the UK.

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Re: About to purchase new 30W!

Post by SamTheDog » Tue Aug 06, 2019 7:51 am

Agreed.... There is / was an eddystone on ebay recently It looked like an XE series... Although there are some superb kits available from..... NRG in New Zealand See http://www.nrgkits.co.nz (or ask the fella above....! ) Not used one of these but I may well try one.... OR see free radio berkeley stuff here... http://www.RFEMPORIUM.COM I have used this gear before...
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And many moons ago.. WNKR on FM and Shortwave.
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