So throwing in an RX pre-amp wouldn't help much either, then... hehehehe Thanks, Bob! Mark - N9WYS
-----Original Message----- From: Repeater-Builder@yahoogroups.com On Behalf Of [EMAIL PROTECTED] Sent: Saturday, June 07, 2008 11:35 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: antenna suggestions for 440mhz At 6/7/2008 08:22, you wrote: >In fear of moving off topic... I'd like to ask how one can determine the >electrical downtilt of an antenna? > >I just put into service a RSF/Celwave Super StationmasterR Model 10017-6 >that is designed for 925-960 MHz on my 927.5250 repeater. The added gain >factor of the antenna (an additional 4dBd over what was previously in place >- a Decibel DB586-Y) does not seem to benefit the receive (at 902 MHz). I >gained what seems like a little extra receive range, but not equal to what I >seem to have gained in transmit coverage. Downtilt shouldn't vary too much between TX & RX freqs. What's probably happening is that the increased gain is resulting in increased noise pickup from the horizon as well as signal. Changes in gain directly affect your transmit ERP, but they don't necessarily translate directly into increased RX range depending on where the noise is. Slightly related: I once maintained a repeater at a residential mountain site with lots of elevation but no clear view to the ground (trees in the way). The site RF characteristics on 2 meters were somewhat like an RF "black hole": RF could get in but was hard to get out. We needed ~200 watts of TX power on the repeater to balance TX & RX with a 50 watt mobile user. I believe the reason was foliage absorption combined with a high noise floor down below. Around here antenna noise temperatures on 2 meters are typically ~3000 K. However this site had much lower noise - it's the only site around here where adding a preamp to a G.E. receiver resulted in actual system sensitivity improvement. So with biological attenuation surrounding the site, both signal & noise approaching the site were attenuated. With the low noise RX, the net reduction in S/N due to the attenuation was minimal. However, the attenuation directly reduced the TX signal leaving the site. So the net effect was the site "heard" OK but TXing out was difficult. Bob NO6B ------------------------------------ Yahoo! Groups Links No virus found in this incoming message. Checked by AVG. Version: 8.0.100 / Virus Database: 270.0.0/1489 - Release Date: 6/7/2008 11:17 AM
