> Hello,
>
> I have a portable spectrum analyzer from Aaronia (Spectran HF-6080).
> The measurements in the GSM900 & 1800, and UMTS bands are (seem to
> be) good and normal.
>
> But at most GSM/UMTS base stations, I found that for example in the
> 5000-6000 MHz range and at 3000 MHz, there are several signals which
> are higher in intensity than the actual GSM or UMTS frequency band
> signals.
> The signals are certainly coming from the base stations. The high
> values between 2099 - 3011 Mhz (and further) are only detected at
> base stations where GSM900/1800 and UMTS antennes are installed,
> not at those without UMTS. The 3000 MHz frequency is normally
> military. The high signals between 5000-6000 Mhz are almost always
> found at all base stations, and seem not to be WLAN (also not the
> typical sound from WLAN/WIFI).
>
> There might be some (small) errors in the measurements of the
> Spectran
> in these higher bands (?), and some "mirror frequencies" (not real)
> might exist in the range that I am measuring (at pulse mode), but
> I measure several ranges separately (for example the 2099-3011 MHz,
> 5470-5725 MHz, 5725-5825MHz ranges) and found that the high signals
> are very clear and also hearable (audio analysis), in many cases at
> around 200 meters from the base ststions ca. 2-6 V/m, in contrast to
> the for example 0,2 - 1,2 V/m values in the GSM / UMTS bands !
>
> I think these high signals can be real, possibly 'intermodulation
> interference signals' (and out of band). I read a lot on the
> internet
> about measured signals and that all spectrum analysers have the
> problem
> of second and third (...) "harmonic frequencies", "intermodulation
> interference" from several different base station antennas, "mixing
> products from harmonics", etc, and that the problem is becoming more
> important, as more different antennas are being installed at each
> base station.
>
> See for example
> http://www.tek.com/Measurement/App_Notes/2G_14758/eng/2GW_14758_0.pdf
> and
> http://www.summitekinstruments.com/oasis/documentation.asp
> click on "White Paper".
>
> The 900 (gsm) and 2100MHz (umts) signals from base stations could
> indeed also mix and give something around 3000MHz, and the readings
> between 5-6 GHz could also be explained by (third order) harmonics
> and mixing ?
> The not-real 'mirror' signals ("in" the measured range) are normally
> weaker, but can the real (really in the air) signals
> like "intermodulation/mixing/harmonics" signals be more stronger
> than
> the original signals separately ?
>
> At 2400MHz, 3000MHz, 3500MHz, 5000-6000MHz, the sound (audio
> analysis
> of pulses/modulations) with Resolution Band Width (RBW) at 3 MHz and
> 1 MHz is a loud constant noice, almost the same (?) like at
> GSM1800/UMTS
> (base control carrier) but it seems a little different and in most
> cases
> more intense. At RBW 300 and 100 kHz, the sound is clearly with
> small
> hard pulses (around 10 Hz ?, like woodpecker). Can anyone explain
> this ?
>
> I also noticed that when I put my GSM on (in speaking mode), high
> signals
> in the 3000 MHz and 5000-6000 MHz range are also found (and in audio
> analysis also clearly the sound of a GSM). This can also be
> explainedby "intermodulation/harmonics/mixing" signals ?
>
> Best regards,
> Joris Everaert
> Biologist
> Belgium
>