antenna range queries

hi,

just wondering how true this scenario is.
testing the range distance for an 800/900MHz band. For 800MHz can go until 5km distance average while at 900MHz band, the distance is only 3km. s11 and efficiencies are relatively good for both bands. Power levels are the same for both bands.
The thing is my country is using the GSM-900. Could this be the factor? and why this can cause the HAM radio range distance ?

thanks

hey

sure this can be the problem. try using 915MHz which is not used by GSM and see if it helps.