Unterschiede

Hier werden die Unterschiede zwischen zwei Versionen angezeigt.

--- projekte:3cmcompacttrv:start [2022/03/20 16:02] – yc
+++ projekte:3cmcompacttrv:start [2022/05/23 18:12] (aktuell) – [Transverter PCB] thasti
@@ Zeile 4: / Zeile 4: @@
 {{:projekte:3cmcompacttrv:cambridge_pcb.jpg?600|}}
-First all the details of the modules were reverse engineered(documented [[projekte:3cmcompacttrv:reversing|here]] in german) and a concept for the usage as a 3cm transverter was worked out. A first prototype was tinkered together and performed very well:
+schematics: {{ :projekte:3cmcompacttrv:10g_cambridge.pdf |}}\\
+project files: [[https://git.loetlabor-jena.de/yc/10g_cambridge|10g_cambridge]]
-{{:projekte:3cmcompacttrv:prototype.jpg?400|}}
+First all the details of the modules were reverse engineered(documented [[projekte:3cmcompacttrv:reversing|here]] in german) and a concept for the usage as a 3cm transverter was worked out.
 ===== Concept =====
@@ Zeile 19: / Zeile 20: @@
 ===== Modifications =====
-==== TX Baseband Filters ====
+==== Transverter PCB ====
-The original lowpass has a cutoff frequency of ~12 MHz, which needs to be replaced by
+The transverter PCB is visible on the top of the unit. To perform the modifications shown below, its milled RF shield needs to be removed. For this, only the screws visible on top of the RF shield need to be removed, the PCB itself can remain screwed to the base of the unit.
+=== TX Baseband Filters ===
+The original lowpass has a cutoff frequency of ~12 MHz, which is replaced by a 3rd order 60 MHz filter. From each filter (I and Q, respectively), unsolder four inductors and five capacitors. Replace with components as shown on the picture below.
 {{:projekte:3cmcompacttrv:tx_bb_filter.jpg?400|}}
-==== TX IF Filter ====
+=== RX IF Filter ===
+The original 70 MHz IF filter is not used and the signal path is switched to the second not populated filter footprint. A pcb with a 3rd order 50 MHz bandpass filter was made and fits on this footprint.
+{{:projekte:3cmcompacttrv:rx_if_filter.jpg?400|}}
+schematics: {{ :projekte:3cmcompacttrv:rx_if_filter_scm.pdf | RX IF filter}}\\
+project files: [[https://git.loetlabor-jena.de/yc/10g_cambridge|if_cambridge]]\\
+errata:
+  * PCB pinout is flipped vertically, hence short wires are required to connect RF path to coupling capacitors on the PCB.
+=== TX IF Filter ===
+The original ceramic filter is removed and the attenuators are replaced by 0R resistors. The green inductor at the far end of the line remains in place. Since it provides a low resistance path to ground prohibiting probing for shorts, careful optical inspection of the modification is useful.
 {{:projekte:3cmcompacttrv:tx_if_filter.jpg?400|}}
-==== PA Power Supply ====
+In theory image rejection by the quadrature mixer can be tuned to -60 dBc or better, however thermal drift limits the image rejection to about -50 dBc. A pipecap filter (constructed from a 28 mm pipecap) is therefore inserted between the transverter board and the RF board. It connects in-line using the external MCX connectors.
+{{:projekte:3cmcompacttrv:cambridge_if2.jpg?400|}}
+project files: [[https://git.loetlabor-jena.de/yc/10g_cambridge|if2_cambridge]]\\
+errata:
+  * MMCX instead of MCX used, fix in next revision
+==== RF Board ====
+The RF board is the lower, large PCB enclosed between the two main halves of the body. The RF board is exposed simply by removing the six large screws on the bottom of the unit. The thermal/electrically conductive pad on the bottom might obscure these screws and needs to be removed.
+=== PA Power Supply ===
+The 48V DC/DC module and TR4 are removed. A IRLML6402 is placed upside down on the TR4 footprint as shown in the picture. With two additional wires the drain voltage is switched on when the negative gate voltage is there.
 {{:projekte:3cmcompacttrv:pa_ps.jpg?400|}}
-==== RX IF Filter ====
-{{:projekte:3cmcompacttrv:rx_if_filter.jpg?400|}}