Shorting BNC Caps - What are they used for?

Discussion in 'QRP Corner' started by KD2KUB, Apr 28, 2019.

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  1. KD2KUB

    KD2KUB XML Subscriber QRZ Page

    I attended the Drumlins Hamfest today, and I picked up a variety of BNC Caps for my QRP Kits. Some of them are shorting and others are .5w 50 Ohm load rated.

    Any idea how and what purpose shorting caps are used for?

  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    One use is/was in computer networks that required continuity on every line, even when a device/computer was removed. The shorting cap provided continuity. One example some may recall was the IBM Token Ring, 10 base T, network, made especially popular by Novell Networking. This was popular before Ethernet networking was common.

    The cap with a 50 Ohm or 75 Ohm load is used to maintain characteristic impedance on a coax connection. One use might be when using a BNC "T Connector" to splice into coax connections while using test equipment like Oscopes, Signal generators, spectrum analyzers, etc. When the third port is not in use, an appropriate loading cap is connect to the port to maintain 50/75 Ohm impedance and avoid distorting the signal.
  3. KD2KUB

    KD2KUB XML Subscriber QRZ Page

    Thanks for the explanation on shorting caps. Any real practical use of those shorting caps on Amateur radio transceivers other than for storage?
  4. AA5CT

    AA5CT Ham Member QRZ Page

    I try to keep little rubber red 'caps' on all my test equipment I/O connectors (when not in use) on account of dust accumulation ... also physically protects them in transport!
  5. K8ERV

    K8ERV QRZ Member QRZ Page

    You can put them on your head when it rains---

    TOM K8ERV Montrose Colo
  6. KE5MC

    KE5MC Premium Subscriber QRZ Page

    In line with WB5WPA's post I will add there is a third type of open style. Typically they have a short ball chain which is attached to the face of the equipment. Keeping them from getting lost, well that the theory anyway. Its is easy to knock the outside cylinder of the female panel mount connector out of round. Very difficult to get it back to usable geometry. For my Elecraft KX3 I attached one to keep the BNC safe when in the wild.
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    You could use them to make Coax Stub filters. :)
    WG8Z and AD5HR like this.
  8. W4XXV

    W4XXV XML Subscriber QRZ Page

    I JUST saw this last night... great timing.
    W2AEW has a great youtube channel, and covers an application for them in
    #299: How to build an Open - Short - Load (OSL) Calibration kit for HF Antenna Analyzer


    Cam - W4XXV
  9. N8TGQ

    N8TGQ Ham Member QRZ Page

    I wonder if the 50 ohm caps could be used as dummy loads.
  10. VA3VF

    VA3VF Ham Member QRZ Page

    Yes, but only up to about 250mW or so.
    KA0HCP likes this.

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