Re: [144MHzEu] Out of band QRM. Worst case ?

[Henk <j.h.devries@xxxxxx>]

Hi Leif,

In Belgium. Luxemburg and the Netherlands POGSAG paging systems are in
operation above 144 Mc using a dense transmitter network
They are around 154, 159 and 162 Mc. Also the ERMES paging system is
operational in the Netherlands.
Powerlevels range from 100W - 250W, with 2-5 dBi antennas at 50 - 100 m
AGL.

The produced fieldstrenght is quite high. The minimum at the outskirt of a
transmitter-range is 55 dBuV/m with >90% probability . Therefor in most
cases a significantly higher fieldstrenght is produced.

best regards
Henk PA0C



----- Original Message ----- 
From: "Leif Åsbrink" <leif.asbrink@xxxxxxxxxxxxxxxx>
To: "Linrad" <linrad@xxxxxxxxxxxxxxxxxxxxx>; "Moon-Net"
<moon-net@xxxxxxxxxxxxxxxxxxxx>; "144mhzeu" <144mhzeu@xxxxxxxxxx>
Sent: Saturday, March 13, 2004 12:10 AM
Subject: [144MHzEu] Out of band QRM. Worst case ?


> Hi All,
>
> I am going to make a front end for 144 MHz that will fit
> the WSE converters and Linrad.
>
> There will be two RF amplifiers, one preamplifier for
> mounting in the tower and I will probably not make them
> since such amplifiers are available from many sources.
>
> The noise figure of RX144 will be about 11 dB and there
> is a need for a second RF amplifier with high IP3.
>
> The idea is to have a tower mounted preamp with a
> gain (including cable losses) of about 15 dB followed
> by a high level amplifier with a noise figure of
> about 2 dB that will add about 10 dB gain.
>
> A good preamplifier may have an output IP3 of +25dBm.
> The input IP3 of the RX144 is about +20 dBm but if
> both signals fall within the passband of the RX70, the
> input IP3 is only +15 dBm.
>
> After adding the second RF amplifier, the IP3 mis-match
> between a +25 dB IP3 preamplifier and the Linrad system
> amounts to 20 dB for in-band signals.
>
> The in-band input IP3 (at the antenna) will be -10 dBm
> while compression will start at something like -20 dBm.
>
> The second RF amplifier could incorporate a filter that
> converts in-band interference to out-of-band interference.
> Are there any signals within 10 MHz from the 2 m band that
> could produce more than -30 dBm so they would be near blocking
> or is there any risk for a signal pair that could produce
> third order intermodulation on 144 MHz ? Two equally strong
> in-band signals at -50 dBm would give IM3 at -130 dBm which
> would be well audible.
>
> As far as I know there is nothing here in SM but I do know
> there are pagers just below 144 MHz in the UK. It will be
> fairly easy to design filters that make performance limited
> by the mast mounted preamplifier for signals that are more
> than 4 MHz outside the band edges if one wants full sensitivity
> from 144 to 146 MHz. Likewise it would be fairly easy to make
> the system limited by the preamplifier for signals below 142.5
> or above 146 MHz if one wants full sensitivity from 144 to
> 144.5 MHz only.
>
> My question is: Is there a real need for better than this?
>
>
> 73
>
> Leif / SM5BSZ
>
>
>
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LINRADDARNIL