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Old 9th Feb 2011, 3:24 pm   #21
Skywave
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Thumbs up Re: MW Transmitter with built in fading - suggestions

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Originally Posted by Station X View Post
How about....Get a cheap radio and tune it into a station which really does fade in and out. Feed the AGC voltage from this radio to your micro transmitter and use it to vary the RF output power.
That idea I like! Simple; easy to implement. Almost 'space diversity' in reverse!

Al.
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Old 11th Feb 2011, 11:59 pm   #22
boxdoctor
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Default Re: MW Transmitter with built in fading - suggestions

Subjectively, a lot of the "fading" effect was not only the volume of the received signal, but also phase distortion caused by diverse propagation paths of the transmission resulting in signal arriving at the receiver at different times.To simulate this without resorting to digital processing, you could use a bucket-brigade device with a randomly varying clock rate, and mix the output with the original signal. (And vary the amplitude of the output of course). If you really want to !, Tony
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Old 12th Feb 2011, 12:17 am   #23
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Default Re: MW Transmitter with built in fading - suggestions

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Originally Posted by boxdoctor View Post
you could use a bucket-brigade device with a randomly varying clock rate, and mix the output with the original signal. (And vary the amplitude of the output of course). If you really want to !, Tony
More food for thought, now where did I put that CB echo mike

Cheers n Beers,

David....

Edit. I wonder what a spring Line reverb would sound like?
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Old 12th Feb 2011, 12:29 pm   #24
boxdoctor
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Default Re: MW Transmitter with built in fading - suggestions

David - you no doubt realised that I was referring to delaying the audio signal in my post, not the R.F.!. If your enthusiasm runs to it, you could use two seperate random generators, one for the BBD clock, and one to vary the carrier amplitude. Make the mixing (raw/delayed signal) adjustable though. A CB echo mike sounds like a good basis for experimentation. The BBD clock will only require varying a very small amount to cause the effect required.
I suspect a spring line reverb will sound like ......a spring line reverb. But perhaps worth a try on the grounds of simplicity. Tony.

Last edited by boxdoctor; 12th Feb 2011 at 12:36 pm.
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Old 12th Feb 2011, 11:02 pm   #25
jimmc101
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Default Re: MW Transmitter with built in fading - suggestions

If you fancy experimenting with phasing, Audacity (http://audacity.sourceforge.net/) has a 'Phaser' effect which you could use to see if it gives the sound you want.
I've just had a try with the default settings and it did sound something like the effect I remember.

Jim
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Old 12th Feb 2011, 11:36 pm   #26
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Default Re: MW Transmitter with built in fading - suggestions

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Originally Posted by jimmc101 View Post
If you fancy experimenting with phasing, Audacity (http://audacity.sourceforge.net/) has a 'Phaser' effect which you could use to see if it gives the sound you want.
I've just had a try with the default settings and it did sound something like the effect I remember.

Jim

Now that's a good idea but I will try the phaser in Virtual DJ as I used that extensively for my Mobile Disco before retiring (oldest DJ in town).

I was going to be using a netbook running Virtual DJ in auto DJ mode to provide the music.
I will also try your Idea as well

Cheers n Beers,

David.....
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Old 13th Feb 2011, 3:05 am   #27
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Default Re: MW Transmitter with built in fading - suggestions

Update: I've been on the VirtualDJ downloads page and searched the plugins and found a HQ flanger with the following features:


Quote:
Description:
Improved version of my flanger.
v2.0 Capabilities:
_ Volume
_ Base delay
_ Added/flanging delay
_ Flanger phase (to start where you want, or to align the flanger)
_ Stereo separation (for the rotating effect)
_ Variable flanger length (1/65536 to 65536 beats)
_ Polarity of delay
_ Flanger or Jet modes
_ Reset button to don't get lost
_ Linear interpolating between samples (to avoid bad scaling, but cuts very high frequencies a bit)
_ Separation done between backward delay (default) and forward delay (special)

v2.1 (April 4th, 2010): updated by djcel with the new SDK for PC & mac
v2.2 (April 5th, 2010): code improved
This seems to be recreating the phazing effect OK , I have attached a zip of the mp3 I recorded. It needs a bit more adjustment but is close, what do you think.

Thanks to jimmc101 for putting me on to this idea.

Cheers n Beers,

David.....
Attached Files
File Type: zip test 208 effect.zip (1.52 MB, 59 views)
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Old 13th Feb 2011, 3:53 am   #28
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Default Re: MW Transmitter with built in fading - suggestions

What about a Radio Northsea simulator with added jamming signal
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Old 13th Feb 2011, 4:32 am   #29
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Default Re: MW Transmitter with built in fading - suggestions

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Originally Posted by Andy Doz View Post
What about a Radio Northsea simulator with added jamming signal
Mmmm.... probably just need to overlay some reggae onto the broadcast track and then we'll all be jammin'


Cheers n Beers,

David.....
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Old 13th Feb 2011, 9:34 pm   #30
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Default Re: MW Transmitter with built in fading - suggestions

That sounds good David - all you need now is some random volume variation, and you've got it ! Tony
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Old 18th Feb 2011, 3:40 pm   #31
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Default Re: MW Transmitter with built in fading - suggestions

Quote:
Originally Posted by Andy Doz View Post
What about a Radio Northsea simulator with added jamming signal
Or add a 2kHz tone between dusk and dawn to simulate Radio Caroline South when they (rather stupidly [1], in my opinion) operated off-channel on 1495kHz, causing interference to (and getting their own signal interfered with by) the French night time fill-in network on 1493kHz.

For fading, spit the RF to feed two output stages. Feed one via a variable phase shift network, then combine the outputs. This will simulate the ground wave/sky wave fading that I remember so well in Essex. Variable gain in one channel will be useful - I would suggest the non phase shifted one, because it must be possible to run at exactly the same level in anti-phase to achieve the complete cancellation experienced with very heavy fading.

[1] Much as I was a 'pirate' supporter and avid listener in the mid 60s, I was always appalled by such stupidity, which can only have worked against them as every complaint received by HMG from a legal broadcaster only reinforced their intention to ban them.

The original Radio Caroline, later Radio Caroline North, operated co-channel with Radio Prague - some 1,500 miles away - on 1520kHz and closed down at night 'to avoid interference'. Ten out of ten for that!

I don't know if we will ever know what frequency Radio Atlanta intended to use but, having lost the race to be first, they obviously just plugged in the first crystal they came across that was close to Caroline's frequency. Fine when they first started with short summer nights but, come the winter ...

Then there was Radio Scotland who blasted their powerful transmission across the Irish Sea on the same frequency as Radio Eireann's 1kW Dublin repeater ...
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