Troubleshooting of FB cable

(Be careful with FB cables!)

On weekend nights, I usually communicate with one or two stations via satellite before having an on-air meeting with JQ1YLK, so I often leave the antenna I used for the satellite as it is.
Recently, I haven’t been able to get through to them when I call via satellite… I can hear the beacon quite well, but maybe it’s the uplink?
I thought I’d fix it later, so I went out to OAM, and got messages from local stations saying, “FNN, the signal is really weak today, huh?” “Huh?” I quickly changed to a different GP, but it seemed like something was wrong with the antenna system.
The next day. The antenna itself was a new GP, so I thought that this was probably the only problem, so I removed the coaxial cable connecting the waterproof box containing the outdoor duplexer to the antenna.
I thought for sure that the connector had been submerged in water from the recent rain, but that wasn’t the case.
The connector is an N-type. The cable is a 5D-FB cable. I’ve had plenty of trouble in the past because of poor soldering of the braided wire on the outer shield of M-type cable, so I often use N-type cable at high frequencies, which has no soldered outer wire.
Thinking that it might be the case, I took a look at the core wire and…….ah!




The contact (needle contact point) came out cleanly… What’s more, there was no solder on the core wire of the coaxial cable…

The side hole of the contact where the solder flows in was (seemed to be) completely filled, so it was the perfect example of a weak solder joint.

So what caused this?

I always use a 20W soldering iron to prevent the insulation from melting on the core wire. (On the other hand, I always solder the braided wire of the M-type connector all at once with 60W.)

I think I probably underestimated the fact that the insulation of the FB cable is polystyrene, which is weaker against heat than the 5D2V, and that the N-type contact is small, so I thought it would be easy to solder with a 20W iron. However, the core diameter of the FB cable is 1.8mm, while that of a normal 5D2V is 1.4mm, so the cross-sectional area is 1.7 times larger. That’s how difficult it is to heat up, but… I overlooked that.

I will have to check the other N-type connectors as well, but for now I applied flux to the core wire just to be safe, applied some extra solder, and then re-welded it.



It is an FB cable that has little loss and can be easily replaced with a normal cable, but there are unexpected pitfalls if you do not treat it with the proper care.

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