FM Transmitter advice

[rubber-man]

Hi all im new here but not new to radio although I am new to band 2 pirate radio. I have been fascinated with pirate radio since the mid 80's and now I have finally built a radio station. I have a 10 channel mixer with a pitch shifter which will disguise my voice and a dipole in my attic fed with RG8 coax, Everything is computer controlled. Reason I wanted to build it is because where I live the local station plays nothing but rubbish Anyway all that is left is a transmitter and I have been looking at the CZH-7C 7 watt ones you can buy on Ebay, This is plenty to cover my town but can anyone tell me what they are like?

Cheers all...Rich

[yellowbeard]

Welcome Rich. They don't like those chinese transmitters in here at all. They are noisy, produce only average audio and quite a lot of unwanted spurious. That said they are good for the money considering they work out of the box, you would probably need to be able to solder or spend more money to beat them. Some things I can say for sure is if there is any way you can get your antenna outdoors you will do a lot better, 6 of your 7 Watts will be absorbed by the roof - and you are going to need some form of compressor or limiter to prevent overmodulation, you can do that by passing the audio through a computer with the right software.

[rubber-man]

Thanks for the reply. Im situated in quite a good spot over looking my town and have used various antennas in the attic for other types of radio with very good results, Probably because there are so many holes in my roof I can put a dipole outside but it would be much lower down. Im not looking at running a station 24/7 just on weekends really. All the music is on my computer using Winamp and I have used software to compress it and everything is at the same level. I did have a 19 inch rack mounted compressor but I sold it some years back. Im just doing this for a bit of fun really and not trying to compete with the big stations. My dipole is a quarter wave with an RF choke fitted, Im being very very careful not to cause any interference. I have some radio and music recording background which helps too. Any help is greatly appreciated.

[shuffy]

I'd definitely think about getting a limiter if you're going to be presenting on there too. Something simple should do the trick, I think someone posted a design in one of the other threads. Yellowbeard's right with everything he's said about the Chinese transmitters, aside from all the other problems the audio on them is a little "flat" so probably not worth going overboard with your audio chain to be honest.

[sinus trouble]

Greetings Mr Rich!
Mr Yellowbeard told you not to have a transmitting antenna in your loft for good reason!
Not only will surroundings distort radiation pattern, it will saturate your property and possibly neighbours with RF causing serious radio interference!
In particular things like freeview tv and other sensitive recievers are at risk from RF blocking so be aware!
I once used my garden shed as a transmission site with the dipole fitted to a large mast on the roof!
I then used a low power band1 to link to the house!
Also checked with neighbours to see if they had any strange faults with their tv! lol
Happy transmitting!

[Albert H]

If you want ready-built, take a look at the Dutch gear. There are 1 Watt, 6 Watt and 15 Watt versions available. These are truly single - frequency devices with no adjacent spurs, and with good lowpass filters built in, so that their output is clean enough to go straight into your aerial.

If you want stereo, you'll have to add a stereo coder (look for "Katruud" on eBay for really good ones), and you MUST use a limiter.

Get your antenna outside. You'll waste 90% of the aerial energy in heating up the roof if it's indoors. Also, if the town is in one direction from you, you could consider using an "H" antenna, to give a hemispherical coverage pattern towards the town. This will double your ERP (effective radiated power) because you won't waste power towards the farms, trees, woods and sheep!

[sinus trouble]

Agreed With Mr Shuffy And Mr Albert!
A limiter is essential, sound quality? yes! but more important is deviation! you dont wanna end up bleeding into adjacent stations!
The problem with those CHZ transmitters lies with the source! They are based on the BA14XX ICs Which are cheap "all in one" devices that are not designed to be amplified!

[yellowbeard]

I can't help wondering if there is a market out there for a halo antenna that looks like a weather cock, with a plastic NSEW stuck to the dipole and a rubber chicken on a broom handle for the weather vane. Might be a bit rustic for townies, but we have at least two users on here with dipoles in the attic and I do feel bad when they get told about the attenuation and the risk of TVI.

[radionortheast]

This will double your ERP (effective radiated power) because you won't waste power towards the farms, trees, woods and sheep!

sheep problaly like listening in I always thought someone into radio or the old owner of radionecks would drive around in a car, instead of a silver lady on the front there would be a halo it would look cool, a dipole in the loft will problaly reach the town better than a halo poorly matched outdoor aerial

[Sietedj]

Hi, I have a CZH-7C 7 and have had no problems of interference, if not amplifiques, there do not know what would happen. The sound is not bad, but as I have said the chip that carries all inclusive is not the best. Look at other options.

[rubber-man]

Cheers everyone for the advice. Ok so I have got my hands on a 21 foot scaffold pole which I am going to mount outside with the dipole on top and change the coax to RG213. The dipole is a 1/4 wave, Do you think a 1/2 would be much better? Those Chinese transmitters claim to be stereo but I take that with a pinch of salt. Like I said it's not going to be a big 24/7 station and im just doing it for fun but im being very careful about causing interference. Im a licensed ham op but I mainly work a lot of DX on the 11M freebands so my garden is already full of antennas. I have been looking for a low pass filter for VHF but cant seam to find any only ones for HF , Anyone know where I can get a VHF low pass filter? Also a lot of pirate stations seam to play dance/drum N bass etc, Why is this? Im an old metal head so it's going to be a rock/metal station. Again thanks for all the help. Excellent forum this.

Rich

[Maximus]

The problem with a lot of the Chinese transmitters is "in band interference". I used to see a lot of hedgehog spurs either side of the main carrier. This causes problems with other radio stations on the fm band.

Slightly o/t, I used be greedy and ran a 150w rig to cover a small town that was 2 miles in diameter. Still no interference on any of the legals, you just didn't need any aerials connecting to your tuners. All using Dutch gear


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[rubber-man]

Anyone got any links to these Dutch transmitters? Also I found this...

http://www.ebay.co.uk/itm/STEREO-LIMITE ... SwbsBXlejM

Will this do for what I want?

[yellowbeard]

I am not familiar with the ebay item, but it looks like it'd be rough and no adjustments on it to make it nice, it'd be better to do the limiter process on a computer - almost any old computer will do and it can sound is really good. There are a few good Dutch sources for transmitters, heres a couple to get you going:

Code: Select all

http://dutchrfshop.nl/
http://www.hf-electronics.nl/

Halo antenna 144MHz (without the rubber chicken)

Code: Select all

http://www.qsl.net/kp4md/144_mhz_halo.htm

[Maximus]

Anyone got any links to these Dutch transmitters? Also I found this...

http://www.ebay.co.uk/itm/STEREO-LIMITE ... SwbsBXlejM

Will this do for what I want?

dutchrfshop.nl

hf-electronics.nl

I think there was some kind of strange law that was invoked recently that stops them from advertising equipment or something. But if you drop them an email asking for their product listings, they'll be more than happy to help.

Theres also PCS-Electronics, but I've never tested their kits. Plus I think they cost a bit more.

I've never had a problem with the Dutch gear and everyone's more than happy to assist with any technical questions.




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[radionortheast]

Also a lot of pirate stations seam to play dance/drum N bass etc, Why is this? Im an old metal head so it's going to be a rock/metal station. Again thanks for all the help. Excellent forum this.

Rich

who knows think its been talked about else where, I don’t like to offend anyone lot of times its about impressing mates don’t want play anything they wouldn’t like, so I guess that means a narrowing of the music been played. I mostly listen to music here on my own so I just pick out whatever I like, the only music I don't like is jazz.

[Albert H]

Whenever I've "borrowed" other people's transmitters, they usually get something really outlandish like Ornette Coleman or something "classical" - Bach, Brahms, Chopin or whatever. It really confuses the hell out of the "Hackney 'mitter men"! When Project had a seriously big rig on 106.5MHz, not far from my place, one night they suddenly started transmitting some really obscure late 60s Jamaican Ska! It's quite good fun, lets the kiddies know that they don't own the airwaves, and really pisses off their "engineers" (who are almost universally clueless, these days!)

[sinus trouble]

a lot of pirate stations seam to play dance/drum N bass etc, Why is this? Im an old metal head so it's going to be a rock/metal station. Again thanks for all the help. Excellent forum this.

Rich

Hello Rich
I think its a bit narrow minded to say that! Early pirates like Caroline played Rock n Roll stuff! 90s stations focused on the rave/club scene! Also there are many Ragga, RnB, African and Turk stations on air! Just because you don't listen to them? It does not mean they don't exist!
Pirate Radio is all about an alternative to the usual commercial guff!!
Your station will have its own identity! Whether that is 'Soft Rock' 'Hard Rock' 'Death Rock' ??
Its your choice!

[halfwave]

Hi Rich,

I too have a small station, with a loft mounted aerial (now a 1/4 ground plain).
I have a CZE-15B which is hooked up to my pc, which I am only using @ 7watts,
which gives me coverage for what I need.

As I am only just starting out I did not want to spend lots, just wanted to get
set up and see how it all goes, then I can always get something better
at a later date.

My Set-up
I currently use RadioDJ software, which is Free software and has loads of features
and is hands down way better than WinAMP for a radio station application.
http://www.radiodj.ro/

Also I use Stereo Tool for a software Compressor/Limiter, which you can
use the WinAMP Plug-in which is available on their site, within RadioDJ and it makes a
massive difference to the audio. Note that some features need registration to
use without the addition of beeps and a message being played. But just using
the basic free features and tweaking to suit will help a lot.
http://www.stereotool.com/

Make sure you use a dedicated Sound Card, (not on-board sound), if possible one
that can handle 192KHz/24-bit.

One problem I did have was a loud humming on my broadcast, which I thought was
due to me previously using the on-board sound. So I bought a dedicated soundcard
and put it in, but the humming was still there.

After a bit of investigation, I found out that it was when I use the additonal software
for controlling the CZE-15B transmitter from the PC via USB cable. Once I unplugged the
USB cable and killed the controller software the humming went.

Hope some of the above is of use.

btw.
Has anyone here been caught running a small low power station from their house?
If so, what are you likely to be faced with?

[rubber-man]

Thanks Halfwave, Your setup is sounding a bit like mine. Im going to be lazy and try the CZE 7 watt transmitter first and see how it goes. I'll look into that software later. My soundcard is an M Audio 2496 which is a very nice soundcard, I used it in my main recording PC when I had a home music studio and it blows away any Soundblaster card or on-board rubbish.

Oh and getting back to me thinking all pirate stations only play dance and drum N bass...Well I suppose I have been watching too many videos on youtube, You know the ones.

Thanks again...Rich