S59DEM VHF Contest Setup
1. Introduction
Due to the fact that antenna gain can only be achieved by narrowing
the main radiation beam the only way to increase the score in the VHF
contest is to use more than one antenna to cover as much of
the azimuth as needed (i.e. all the areas with high activity). More
about this was said at regular S5
VHF&up meeting in Nemčavci 2011 (also available in Czech - tnx to OK1UBO).
2. S59DEM 2m Contest Setup Description
Setup is composed of:
- antenna selection switch on IF
- non-blocking 4 antennas to two modified FT-1000mp (non reproducible
design; covered, uncovered-flipped)
Full setup is not fixed and it changes in minor details
almost before any contest. The IF part is more or less fixed, but power
distibution and number of antennas do change regularly.
2. RX
3. TX
4. RX Settings
With preselector in line the preamplifier in FT-1000mp can be freely
turned on (AIP OFF). With the preselector and antenna switch
insertion loss of 5 dB the total RX NF degrades by 1 dB
for AIP ON case.
5. TX Settings
Several components in the TX chain need to be carefuly set to
achieve best transmit signal quality.
- FT-1000mp
- Proc Gain 2 dB (9:30h)
- XTAL-box-14M - Pout
potentiometer set to max power minus 1dB
- XVRT - Pout between 10 to 30 W
(input TX IF amplifier bypassed)
- PA - at least 1 dB below max
rated power (400W for 500W amp; 800W for 1kW amp)
The Pout potentiometer on preselector is now the main Pout regulation point
(no more playing with rear mounted potentiometer on XVRT).
After final Pout is correctly set, the power should be reduced by 1 dB
with preselector Pout control and then increased back by 1 dB with the
XVRT Pout potentiometer.
This way we have Pout control range with preselector
potentiometer between +1 dB (+25 %) and -8 dB (6 times less).
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Date published: Sept. 2012
