RVFD · Radio Bridge · Bench Build

J7 whip build & DB9 modification

Everything hard happens at the bench. The attic job becomes: crimp one plug, plug in the whip, secure it.

1 The architecture

DRA-30DB9 · rack

28 ft Cat6aexisting run

RJ45 ↔ RJ45T568B · attic

2 ft whipnew

J7 AUXDB25 · repeater

Red-outlined segments are what you're building. The DB9 stays where it is and gets one wire added.

Why

Two problems, one cable. The front-panel 4P4C tap went silent — its level lives behind a software attenuator we can't reach without the Tuner app. And carrier detect has been running on VOX, which only trips for split-seconds and never holds.

J7 fixes both. Pin 7 is a fixed 330 mVrms output with no attenuator in the path. A GPIO set to CSQ Detect gives the node a real hardware carrier signal, so VOX is retired entirely.

2 T568B — both RJ45 ends

Looking into the plug with the gold contacts toward you and the latch down, pin 1 is on the left.

RJ45 pin	T568B conductor	Our function
1	White/Orange	PTT ground (future)
2	Orange	PTT (future)
3	White/Green	RX audio ground
4	Blue	TX audio (future)
5	White/Blue	TX ground (future)
6	Green	RX audio
7	White/Brown	COS ground
8	Brown	COS (CSQ Detect)

Green looks wrong but isn't. T568B splits the green pair across pins 3 and 6, which aren't adjacent. That's correct — 3 and 6 are electrically the same twisted pair. Don't "fix" it to 3 and 4.

3 The whip — RJ45 → DB25

Build from an offcut of the same solid Cat6a. About 2 ft, or whatever reaches comfortably from the coupler to J7.

RJ45 pin	Conductor	Function	DB25 terminal
6	Green	RX audio · 330 mVrms	7
3	White/Green	ground	9
8	Brown	CSQ Detect → COS	4
7	White/Brown	ground	9
4	Blue	TX audio (future)	1
5	White/Blue	ground	9
2	Orange	PTT (future)	2
1	White/Orange	ground	9

J7 — DB25 male, mating face (pins toward you)

7 = RX audio 4 = CSQ Detect 1 = TX audio 2 = Ext PTT 9 = ground

You don't need to decode DB25 orientation. The breakout board's screw terminals are printed with pin numbers — just match the number. The diagram is only for sanity-checking your work.

Cut ~2 ft of solid Cat6a. Feed it through the breakout case's exit slot first.
Crimp one end RJ45, T568B, with your IDEAL solid-core plug.
At the DB25 end, cut the shield back flush and insulate it — the shield stays floating at the repeater.
Land per the table: Green→7, Brown→4, Blue→1, Orange→2.
Twist the four white conductors and land them all on pin 9. Pigtail to a single lead if the terminal won't take four.
Snug every screw, tug-test each wire, close the case.

4 The 28 ft run — attic end

Cut off the old 4P4C pigtail and any mic-jack termination.
Crimp RJ45, T568B — identical order to the whip.
Coupler or keystone jack. Do not bond the shield to the box or chassis — it stays floating at this end.
Snap 3 ferrites onto the main run within a few inches of the connector.

5 The DB9 end — one wire + one jumper

The only soldering in this build, and it's at the rack.

Conductor	Function	DB9 pin	Status
Green	RX audio in	5	already wired
White/Green	ground	9	already wired
Brown	COS in	2	SOLDER THIS
White/Brown	ground	6	SOLDER THIS
Blue	TX audio out	1	already wired
Orange	PTT	3	already wired
whites	ground	6	already wired

DRA-30 — DB9 female, mating face

5 = RX audio in 2 = COS in (new) 1 = TX audio out 3 = PTT 6, 9 = ground

Do not skip

Install jumper JU1 on the DRA-30 board. Without it, DB9 pin 2 never reaches the CM119A's COS input and the carrier line does nothing. Leave JU2, JU3, JU4 off. This is the easiest step to forget and it fails silently.

DRA-30 board showing jumper and trimmer locations — **JU1** is the jumper block at the **upper right**, nearest the DB9 — top of the JU1/JU2 pair. **R12** is the large blue trimmer at lower-center (RX level — leave near mid-travel; we'll set it by measurement). The smaller trimmers upper-right are **R14/R16, transmit levels — do not touch.**

Open the DB9 hood on the existing cable.
Solder Brown → pin 2, clear of neighbouring pins.
Solder White/Brown → pin 6 with the other grounds.
Confirm the shield is still bonded at this end. Don't change it.
Close the hood. Snap 3 ferrites on within a few inches.
Install JU1.

6 Verify before it leaves the bench

Plug the whip into the coupler and meter the whole chain, DB25 to DB9.

End to end: DB25 7↔DB9 5 · DB25 4↔DB9 2 · DB25 1↔DB9 1 · DB25 2↔DB9 3. All beep.
Grounds: DB25 9 ↔ DB9 6 and 9.
No shorts: every signal pin against its neighbours and against ground. Nothing beeps. This is the one that matters.
Shield isolated at the DB25 end — no continuity from shell or pins to shield.

7 CPS (at the laptop)

Accessories → GPIO Physical Pins → Pin #4

• Feature: CSQ Detect
• Active Level: Low

Leave Pin #2 (External PTT) alone. Write the codeplug. Additive change — an output pin doesn't touch the repeat path, and the repeater keeps repeating throughout.

8 At the repeater

Check clearance around J7 for the breakout case before you commit — it's bulkier than a plain hood.
Unplug the old 4P4C from the front panel.
Crimp/punch the run, mount the coupler or keystone, plug in the whip.
Plug the DB25 into J7 AUX.
Zip-tie both the run and the whip to the chassis or rack rail — terminals must never carry cable weight.

9 Node config (remote)

In /etc/asterisk/usbradio.conf:

carrierfrom = usbinvert     ; was vox — hardware COS now

Polarity check: with nobody transmitting, watch Signal on input. NO at idle and YES on key = correct. YES at idle = flip to usb.

10 What "working" looks like

• rpt xnode 1000 → RPT_RXKEYED=1 sustained through an entire transmission, not flickering
• Repeater audio audible in the app, clean and continuous
• Level near −10 dBFS on open-squelch noise

Once it's in, tell me — I'll measure and set R12 properly rather than guess.