Desoldering F-connector for Battery Pack

In summary, the de-soldering process caused a loss of signal power. The second ground wire was used to match the electrical properties of the coax wire, which restored the signal power.
  • #1
mishima
565
35
Recently I de-soldered an f-connector (coax) from a pre-made circuit board. This consisted of 3 soldering connections, 1 for the center wire and 2 for the braid which was electrically connected through a mounting plate. Then I attached the V+ from a 18V battery to the where the center wire was, and ground to just one of the braid connections. My circuit seems to have experienced some signal loss as a result, and I am at a loss to explain why connecting the 2nd ground would affect anything. As far as I can tell, there is nothing on the circuit board even connected to the ground I left open. Any ideas?

Before this, the battery was connected to a normal coax cable I had stripped, V+ to the center wire and ground to the braid. I'm thinking perhaps coax has some transmission properties that aren't matched by the now present 22 AWG stranded wire. Is that the case?

The signal is in the 950-1450 range. I can provide pics if needed.
 
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  • #2
mishima said:
Recently I de-soldered an f-connector (coax) from a pre-made circuit board. This consisted of 3 soldering connections, 1 for the center wire and 2 for the braid which was electrically connected through a mounting plate. Then I attached the V+ from a 18V battery to the where the center wire was, and ground to just one of the braid connections. My circuit seems to have experienced some signal loss as a result, and I am at a loss to explain why connecting the 2nd ground would affect anything. As far as I can tell, there is nothing on the circuit board even connected to the ground I left open. Any ideas?

Before this, the battery was connected to a normal coax cable I had stripped, V+ to the center wire and ground to the braid. I'm thinking perhaps coax has some transmission properties that aren't matched by the now present 22 AWG stranded wire. Is that the case?

The signal is in the 950-1450 range. I can provide pics if needed.

Yes, pictures would help. Are you saying that you switched from coax to twisted pair? If so, what are the Zo values of the two different transmission line cables?
 
  • #3
I went from this (not my pic, but similar):

fcon.jpg


to this (my pic):

newcon.jpg


On the other side of the RF choke is about 4 inches of 22 AWG going straight to the positive of my battery (the other going to ground, not twisted). I don't know the Z0 values. This is for a radio telescope. My signal for this new setup isn't noisy, it just seems less sensitive when I wave my hand around the dish. I guess it could be anything really, I was just never sure about leaving that second ground open.
 
  • #4
Without a proper RF connector and grounding for your DC power inserter it's no wonder your signal power is down. The F connector provided a ground path across the void of the PC board. I have seen 'cheap' designs that use the connector shell as a DC and/or RF signal path. If you look at your picture the two solder pads on either side of the center pad were once connected by the RF connector. Try soldering a short braid or thin sheet of tinned copper between them (spaced away from the center pad) to see if the signal level increases.
 
  • #5
I just tried connecting the 2 grounds with some alligator clips and you are right, things are back to normal. I really have no idea why it matters though, the ground I left open isn't connected to anything on the circuit board, its just a pad with a ball of old solder on it.

I am measuring the signal with an arduino. With only 1 ground connected I would get a change in signal of about 20, with 2 grounds I get a change in signal of about 50. Can you help me understand why the second ground is necessary?
 
  • #6
mishima said:
I just tried connecting the 2 grounds with some alligator clips and you are right, things are back to normal. I really have no idea why it matters though, the ground I left open isn't connected to anything on the circuit board, its just a pad with a ball of old solder on it.

I am measuring the signal with an arduino. With only 1 ground connected I would get a change in signal of about 20, with 2 grounds I get a change in signal of about 50. Can you help me understand why the second ground is necessary?

Without knowing the complete design of the circuit I can only guess but it's likely some sort of RF ground plane or impendace matching stub.

http://www.maximintegrated.com/app-notes/index.mvp/id/5100
 

Related to Desoldering F-connector for Battery Pack

1. How do I desolder the F-connector from a battery pack?

To desolder the F-connector from a battery pack, you will need a soldering iron, desoldering wick, and flux. First, heat up the soldering iron and apply a small amount of flux to the F-connector. Then, place the desoldering wick on top of the soldered area and press down with the soldering iron. This will melt the solder and allow the wick to absorb it. Repeat this process until all of the solder has been removed and the F-connector is free to be removed.

2. Can I use a desoldering pump instead of desoldering wick?

Yes, you can use a desoldering pump instead of desoldering wick to remove the solder from the F-connector. However, it may be more difficult to control the amount of suction and clean up any excess solder.

3. What is the purpose of desoldering a F-connector from a battery pack?

Desoldering a F-connector from a battery pack allows you to replace the connector with a new one if it is damaged or not functioning properly. It also allows you to remove the battery pack from a device without damaging the connector or surrounding components.

4. Can I reuse the F-connector after desoldering it?

It is possible to reuse the F-connector after desoldering it, but it is not recommended. The heat from desoldering can weaken the metal of the connector, making it more prone to breaking or failing. It is best to replace the F-connector with a new one for optimal performance.

5. Are there any safety precautions I should take when desoldering a F-connector from a battery pack?

Yes, it is important to take safety precautions when desoldering a F-connector from a battery pack. Make sure to wear protective eyewear and work in a well-ventilated area. The soldering iron and desoldering wick can get very hot, so use caution and avoid touching them directly. Also, make sure to unplug the battery pack and any other power sources before beginning the desoldering process.

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