Acom 700S, Operating Manual, Page: 17 / 30

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- improve the RF grounding system: use the shortest and widest possible metal strips for the
connections to ground and between the different gear in the shack; connect one or more
counterpoises (sized for the problematic band) to the feeder shield at the point, where it enters
the building, and the same point - with the possibly shortest and widest connections - to the
grounding system: this is a very efficient measure, in particular if the shack is located on a high
floor above ground;
- to reduce the RF impedance of the grounding connections sheet metal stripes instead of flexible
braids are preferred;
- thread ferrite beads or snap-in ferrites with medium permeability (800-4000) over the power
cord, the feeder and the signal cables leading to the affected devices (TV etc); besides the
size, consider the frequency range in which the offered ferrites are effective – normally they
are optimized for suppression of interferences on HF (with larger permeability), with medium
permeability for HF-VHF or with low permeability - only the VHF range. The latter are ineffective
for HF;
- whenever possible use shielded cables and ground their shields at both ends;
- the addition of even quite simple low pass L/C or R/C filters directly to the disturbed inputs or
outputs of the devices is very effective, provided it is practically applicable.
Last but not least, bear in mind that the benefit of the above measures is two-fold. Firstly - they reduce
the interferences from your transmissions to the ambient environment and secondly - they reduce the
background noise floor for your reception. Practically, with no great efforts, implementing the above
measures, you can reduce the background noise floor with one or more S-units across the different
bands. This will allow you not to miss weaker stations, which will hear you because of your increased
transmission power.
4. AMPLIFIER OPERATION
4-1.
Change of modes RX/TX and Operate/Stand-by; AUTO OPERATE
option
a) In Stand-by mode, as well as in the unpowered state, receiving and transmitting (no
more than 200W) with the transceiver is done via RF bypass between RF INPUT and
RF OUTPUT of the amplifier. In Standby, the transceiver’s RF power is not amplified, the
control KEY-IN input does not affect the operation, and the KEY-OUT output (S. 2-3(c))
follows the state of the KEY-IN input unconditionally. The bands cannot be changed neither
manually nor by CAT or remotely.
b) In Operate mode the receive-transmit (RX/TX) direction is controlled by the KEY-IN input:
- at open KEY-IN (Operate/RX mode), the transceiver receives the signals from the antenna
through the same RF by-pass path between RF INPUT and RF OUTPUT as with amplifier
turned off or in Stand-by mode;
- at grounded KEY-IN ((Operate/TX mode) the RF drive is amplified and fed to the antenna
through the RF OUTPUT connector.