Improving 2 Meter repeater at Murree
11 years 2 months ago #5
Last weekend a visit was carried out to improve the performance of 2 meter repeater installed at Mike area. Following HAMS participated in the activity;
Back up support was provided by;
AP2DIG, AP2NK, AP2STA, AP2AKM, AP2SAH & AP2TT
The focus was to improve upon the receive as well as transmittion of the repeater. For that aA Power amplifier of 60 watts was added and an antenna height of additional 50 feet was given to the RX antenna.
Backup support stations intimated that TX signal went considerably stronger with clarity in the audio whereas AP2AKM was able to transmit from his porch operating Mobile 10 watts from Peshawar.
Over all the experiment went well with remarkable improvement on both RX and TX.
Next visit will be carried out to add CTCSS on TX of the repeater.
I would like to share my recent comprehensive discussion with ICOM Engineer regarding CTCSS addition on the TX side of PARS repeater.
Here is the conclusion of our discussion :
1)No doubt Bypassing 200HZ filter will through same CTCSS code and same CTCSS levels as PARS repeater receives on its RX and transmit the same and It will somehow resolve our requirement for linking repeaters . But the point to consider is that strong signals at the RX of PARS repeater will only help to active linking repeater to meet the CTCSS decoding standards.
CTCSS levels are different on all radio sets communicating with main repeater thus the output CTCSS level from main repeater will vary accordingly. Many times a station's PL tone will be enough to access the main repeater, but not enough to pass through and activate the next linking repeater.
This modification only favors Strong transmitting signals received at PARS RX . Weak Signals or noisy signals at PARS RX side will also bring weak CTCSS levels and linking repeater will not activate due to the lower and different CTCSS levels so this is a bug - flaw in that modification as suggested by ICOM.
2)As a professional practice separate ENCODER is required so that it can be fixed on certain CTCSS levels and inject it at the PIN3 marked as “MOD” on the TX board of the MAIN PARS REPEATER (highlighted in the pictures) . Once CTCSS level is fixed then it will leave no effect on the linking repeaters .
3)Injecting CTCSS through microphone input is not possible because of high pass audio stages that may block low frequencies or decrease CTCSS levels before it reach at ‘MOD” section.
Any comments or suggestions are welcomed!
AP2NK , AP2MKS , AP2AUM , AP2GH for their kind attention.