Differences

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--- member-projects:tait-cross-band-repeater [2025/08/02 17:50] – [EMF Calculations] m0lte
+++ member-projects:tait-cross-band-repeater [2025/08/09 21:35] (current) – [Cable] m0lte
@@ Line 34: / Line 34: @@
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+In the official cable there is a board. Most of it can be ignored, however both the audio lines are connected to ground via 600 ohms, and have 4.7uF inline. During the event I did not have this cable, and I found I was transmitting distored audio - I suspect omitting the resistors and maybe the DC blocking capacitors was responsible for this. So I recommend adding at least the resistors.
+Board- important bits highlighted.
+{{:member-projects:tait-8000-crossband-cable.png?900|}}
 ===== Settings =====
@@ Line 77: / Line 83: @@
 There are a bunch of settings you can tweak to reduce the turnaround time, including:
-- PTT debounce time (default 10ms)
+  * PTT debounce time (default 10ms)
-- Lead-out delay
+  * Lead-out delay
+  * others... need to look up
 ===== Antenna System =====
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 W = 44dBm
 dBm (transmitted power level) - 60dB (isolation) = -16dBm
+  -16dBm = 0.0000251189W = 0.0251189 mW
-The Tait TM8100 specification manual states "no degradation after 5 minutes exposure to on-channel signals at + 27 dBm (2.2 V)" - we are 43dBm clear of this so we are a very long way from damaging the receiver. -16dBm is a pretty strong signal (-93dBm is considered 5/9 at VHF and above, so this is "77dB over 5/9") but the Tait filtering and receivers seem excellent and don't appear to be desensitised.
+Pretty low for a transmitted signal, but pretty high at a receiver input.
+The risks are:
+  * densensitisation (receiver is temporarily deafened by a nearby transmitter)
+  * damage (receiver is permanently damaged by much higher signal voltage than the circuitry can withstand)
+The Tait TM8100 specification manual states "no degradation after 5 minutes exposure to on-channel signals at + 27 dBm (2.2 V)" - we are 43dBm clear of this so we are a very long way from damaging the receiver.
+However -16dBm is a pretty strong signal (-93dBm is considered 5/9 at VHF and above, so this is "77dB over 5/9") but the Tait filtering and receivers seem excellent and don't appear to be desensitised in practice.
 ===== EMF Calculations =====
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   * Information: https://rsgb.org/main/technical/emc/emf-exposure/
   * Calculator: https://rsgb.org/emfcalculator
+===== Physical layout =====
+I recommend rigidly attaching the two radios to each other and to a baseboard - this can be cheaply achieved using "all round band" - the 12mm stuff has perfect hole spacing for the Tait side threads.