Parks Medical Electronics, Inc.



Troubleshooting Strange Noises From The Doppler
AFFECTED MODELS: All Parks dopplers

On occasion there are noises you might not expect from the Doppler when in fact the Doppler is working fine.  The following are some common concerns and their causes.

Popping scratchy noise sounds when the probe is first placed on the skin. Air bubbles in the gel are moving and/or popping.  Hair movement can also cause these noises. Use a new dab of gel that looks clear, push the probe down enough so hair is immobilized, and wait a few seconds for everything to settle.  If the noise is not there when the probe is clean (no gel) and suspended in the air, the Doppler and/or probe are probably working fine.
Static when the dry probe is moved through the air. Loose connectors where the probe connects to the instrument, broken shield wire in the cable either at the connector or as it comes out of the probe. There is normally some static generated when the cable is flexed, but it isn't severe.  Replace probe or get connectors fixed.
High pitched tone and flow indicators (if so equipped) go to the extreme. Radio interference from a mobile service, police station nearby, even another Doppler working close by. Usually occurs near large open windows, rarely in the center of a building. Move the Doppler to another location away from windows and toward the center of the building.
Buzzing noise that almost obliterates the Doppler signal. Electrocautery or other sparking device, bad fluorescent light fixture or neon signs nearby. Move the Doppler to another location away from the interference.
Howling noise when probe is held or laid on a table with gel on it. Probe is acting as a microphone and you are getting acoustic feedback. Wipe gel from probe.  If the noise does not occur without gel on the probe, it is probably working fine.



  1. Use the other frequency and see if you have the same or similar problems.
  2. Try using earphones if you have a howling noise.  If there is no howl using earphones but there is with a speaker, it is acoustic feedback.
  3. Try a different probe; even if it is the wrong frequency it will let you know if the problem is noisy connectors in the instrument or frayed shielding near the probe body.


The problem may simply be a probe or it may be peculiar to the environment in which it is used.  If you have tried the tests and remedies mentioned here and you are still having trouble, please give us a call.

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