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Date: Tue, 16 Aug 2011 22:14:55 +0200
From: wolf_dl4yhf <dl4yhf@freenet.de>
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To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Remote Receiving Antenna: UHF-Link
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Hello Tom,

Yes I use a UHF link, but "only" for VLF, single channel, covering 500 
... 20000 Hz. The dynamic range is somewhat limited as you can see on 
the VLF stream's detail page: 
http://abelian.org/vlf/detail.php?stream=vlf6&page=0
But if strongs sferics are occasionally clipped (in the transmitter) 
doesn't hurt that much for this application.

One important thing was getting rid of the stereo encoder / decoder, 
which I had used in the first setup (it was a cheap "HiFi" wireless 
headphone in the 864 MHz band, which didn't deserve its name. Analog 
stereo wideband FM, but noisy as hell).  Getting rid of the stereo-stuff 
(tap the rx after the FM discriminator) gave a better performance, and 
no aliasing effect caused by the strong Navy transmitters in the 
vincinity of the 19 kHz pilot (there is no 'sharp lowpass' before the 
stereo modulator which would have cured some of the problems).

The currently used stream is still analog, using a modified FM wideband 
TX (which was once a cheap AM transmitter), and a wideband RX. Today I'd 
go for a digital system, something with a 16-bit ADC on the TX, and 
16-bit DAC on the RX side. Not sure if the "bluetooth HiFi wireless 
headphones" sold today would be up to the job. For example, the 
Sennheiser RS 170 (digital, without compression, but datasheet not very 
detailed).

73,
    Wolf .

Am 16.08.2011 21:39, schrieb DK1IS:
> Dear LF-Group,
>
> from time to time UHF-links are mentioned to carry radio signals from 
> a remote receiving antenna positioned in a low QRM-region to the main 
> station. At least Wolf, DL4YHF, seems to have such an arrangement. 
> Having a high local QRM level at the site of my main station I would 
> like to try an active receiving antenna (e.g. mini-whip) about 100 
> meters apart on the flat roof of my garage standig in an open area 
> without individual QRM sources. Available power there is 12 V DC from 
> an 120 Ah accu fed by solar cells for activating the radio controlled 
> garage door. Now the question is how to carry the received signals to 
> the shack. Due to the specifics of the site cables (electric or opto) 
> are impracticable, so I`m thinking about an UHF-link.
>
> For a preliminary test I purchased one of the well-known cheap 
> 2.4-GHz-audio-video-links for wireless connection between tv sets and 
> their periphery. They always offer a video channel and two audio 
> channels for stereo signals. First I analysed the link with signal 
> generator and selective level meter on the workbench. The video 
> channel has a flat response between 3 kHz and about 6 MHz with good 
> linearity in the range from -50 dBm to 0 dBm input/output. Without TX 
> input the RX noisefloor is about  -94 dBm at 24 Hz bandwidth which 
> should be overcome with a preamplifier at the TX input. The audio 
> channels work between 0.2 kHz and about 20 kHz with a strong 
> preemphasis, they are fairly linear between -50 dBm and -10 dBm with a 
> noisefloor of about -80 dBm at 24 Hz bandwidth. In my imagination I 
> alredy saw a mini-whip with the video channel from LF to 80 meters and 
> two crossed loops for vlf with the audio stereo channels on my garage 
> ... but a second test with real band signals at the station RX showed 
> the desaster: due to obviously muliplexing the three channels for 
> transmission there were bad QRM spectra about 500 kHz with a lot of 
> sidebands and intermodulation. Strange that home entertainment sets 
> can accept this but for ham radio it`s absolutely impossible. So my 
> question is how to do it better.
>
>   * Obviously one has to use a single channel link without any
>     multplexing.
>   * Obviously FM is the right transmission mode - are there ISM-bands
>     and link units which offer a signal bandwidth of about 4 MHz?
>   * Could you imagine to feed the whole spectrum of an active antenna
>     with certainly more than 100 dB dynamic range and a bandwidth of 4
>     MHz via such a link or should one insert band pass filters for the
>     frequencies of main interest to reduce the dynamic range being needed?
>   * Do you know any offers for such UHF link modules?
>   * Did you have a similar challenge? How did you manage it?
>   * Any other ideas are welcome!
>
> 73,
> Tom, DK1IS


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    Hello Tom,<br>
    <br>
    Yes I use a UHF link, but "only" for VLF, single channel, covering
    500 ... 20000 Hz. The dynamic range is somewhat limited as you can
    see on the VLF stream's detail page:
    <a class="moz-txt-link-freetext" href="http://abelian.org/vlf/detail.php?stream=vlf6&amp;page=0">http://abelian.org/vlf/detail.php?stream=vlf6&amp;page=0</a> <br>
    But if strongs sferics are occasionally clipped (in the transmitter)
    doesn't hurt that much for this application.<br>
    <br>
    One important thing was getting rid of the stereo encoder / decoder,
    which I had used in the first setup (it was a cheap "HiFi" wireless
    headphone in the 864 MHz band, which didn't deserve its name. Analog
    stereo wideband FM, but noisy as hell).  Getting rid of the
    stereo-stuff (tap the rx after the FM discriminator) gave a better
    performance, and no aliasing effect caused by the strong Navy
    transmitters in the vincinity of the 19 kHz pilot (there is no
    'sharp lowpass' before the stereo modulator which would have cured
    some of the problems).<br>
    <br>
    The currently used stream is still analog, using a modified FM
    wideband TX (which was once a cheap AM transmitter), and a wideband
    RX. Today I'd go for a digital system, something with a 16-bit ADC
    on the TX, and 16-bit DAC on the RX side. Not sure if the "bluetooth
    HiFi wireless headphones" sold today would be up to the job. For
    example, the Sennheiser RS 170 (digital, without compression, but
    datasheet not very detailed).<br>
    <br>
    73,<br>
       Wolf .<br>
    <br>
    Am 16.08.2011 21:39, schrieb DK1IS:
    <blockquote cite="mid:4E4AC760.3000202@kabelmail.de" type="cite">
      <meta http-equiv="content-type" content="text/html;
        charset=ISO-8859-15">
      Dear LF-Group,<br>
      <br>
      from time to time UHF-links are mentioned to carry radio signals
      from a remote receiving antenna positioned in a low QRM-region to
      the main station. At least Wolf, DL4YHF, seems to have such an
      arrangement. Having a high local QRM level at the site of my main
      station I would like to try an active receiving antenna (e.g.
      mini-whip) about 100 meters apart on the flat roof of my garage
      standig in an open area without individual QRM sources. Available
      power there is 12 V DC from an 120 Ah accu fed by solar cells for
      activating the radio controlled garage door. Now the question is
      how to carry the received signals to the shack. Due to the
      specifics of the site cables (electric or opto) are impracticable,
      so I`m thinking about an UHF-link.<br>
      <br>
      For a preliminary test I purchased one of the well-known cheap
      2.4-GHz-audio-video-links for wireless connection between tv sets
      and their periphery. They always offer a video channel and two
      audio channels for stereo signals. First I analysed the link with
      signal generator and selective level meter on the workbench. The
      video channel has a flat response between 3 kHz and about 6 MHz
      with good linearity in the range from -50 dBm to 0 dBm
      input/output. Without TX input the RX noisefloor is about  -94 dBm
      at 24 Hz bandwidth which should be overcome with a preamplifier at
      the TX input. The audio channels work between 0.2 kHz and about 20
      kHz with a strong preemphasis, they are fairly linear between -50
      dBm and -10 dBm with a noisefloor of about -80 dBm at 24 Hz
      bandwidth. In my imagination I alredy saw a mini-whip with the
      video channel from LF to 80 meters and two crossed loops for vlf
      with the audio stereo channels on my garage ... but a second test
      with real band signals at the station RX showed the desaster: due
      to obviously muliplexing the three channels for transmission there
      were bad QRM spectra about 500 kHz with a lot of sidebands and
      intermodulation. Strange that home entertainment sets can accept
      this but for ham radio it`s absolutely impossible. So my question
      is how to do it better. <br>
      <ul>
        <li>Obviously one has to use a single channel link without any
          multplexing. </li>
        <li>Obviously FM is the right transmission mode - are there
          ISM-bands and link units which offer a signal bandwidth of
          about 4 MHz?<br>
        </li>
        <li>Could you imagine to feed the whole spectrum of an active
          antenna with certainly more than 100 dB dynamic range and a
          bandwidth of 4 MHz via such a link or should one insert band
          pass filters for the frequencies of main interest to reduce
          the dynamic range being needed?</li>
        <li>Do you know any offers for such UHF link modules?</li>
        <li>Did you have a similar challenge? How did you manage it?<br>
        </li>
        <li>Any other ideas are welcome!</li>
      </ul>
      73,<br>
      Tom, DK1IS<br>
    </blockquote>
    <br>
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