I have an ICOM 2730a 2m/440 mobile rig in a 2015 Ram 1500. Tx and Rx with truck not running is excellent. With engine running I hear static popping, but only on 2 meters. If I Tx I can hear the popping as the squelch tail fades. Listeners will state "you are scratchy into the repeater". 440 is fine. Antenna= dual band Comet attached to truck bed ladder racks. I have good grounding from the antenna. Power direct to the battery. Negative lead grounded to chassis near battery. Ideas? PappyD WR1Y
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1$\begingroup$ Welcome to the site! $\endgroup$– webmarcAug 1, 2021 at 0:49
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3 Answers
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Since the transmitted signal is affected this must be a caused by interference on the supply voltage. The generator is most probable source for this interference. Simple filter in power supply line: inductor plus capacitor will probably help.
Edit/addition: The pulses or RF noise are present on the supply voltage. Two options: the RF noise is present at the frequency where you are tuned or listening, OR the low frequency "spikes"of the generator are converted IN THE RADIO into unwanted RF or modulation.
Filter in the power supply line options: For the low frequency component I should start with inductance above 1 mH and capacitor 100 uF to ground. For RF-direct one microHenry in series and 100 pF capacitor to ground, as close as the connector to the set (!). One of these filters, or both cascaded, will reduce or remove the interference, descibed as static for the sound, but actually not static.
Just to be sure: may be you have to check the screening of your microphone cable as well.
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$\begingroup$ Thank you....can you suggest a brand or source of such a filter? And, why is the noise heard only on the 2 meter frequencies? WR1Y $\endgroup$– PappyDAug 1, 2021 at 13:31
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$\begingroup$ @F.Sessink I highly respect you for your accurate answers to questions here. But please, move those informative comments to your answer. :-) ham.stackexchange.com/help/privileges/comment -"... Answering a question or providing an alternate solution to an existing answer; instead, post an actual answer (or edit to expand an existing one)" $\endgroup$ Aug 1, 2021 at 22:34
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$\begingroup$ "A comment on an answer should be discussing how to improve the answer. Comments are ephemeral and for the purpose of improving the post they are commenting on, not for containing the information that post should have. The idea is to edit all additional facts into the question so that anyone coming to the page later does not need to read any of the comments — the “conversation in the comments” should be for working to create the question and answer in their best form, not for containing them." (Quoted from Kevin Reid) $\endgroup$ Aug 1, 2021 at 22:43
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1$\begingroup$ @Mike Waters: Tnx for instruction and explanation. My comments are moved to the answer. $\endgroup$– user16925Aug 2, 2021 at 16:04
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Check this presentation. There are some recommendations regarding mobile antennas. One of them is to interconnect all the car body's parts (e.g., page 55), preferably using cables or braid directly screwed on the parts (screwing would be more important when operating on HF and lower bands, though; on 2m/70cm, "looser" connections might be effective enough, as the capacitance between the connector and the body part will probably perform a low reactance on such frequencies). Take a look and if you'd think it's feasible for you, give it a try. Besides, I may be mistaken, but I believe that the negative lead shouldn't be connected to the chassis (I'm assuming you are talking about the battery's/transmitter power supply's negative). I'd suggest you to experiment transmitting without such connection in place.
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General.
To solve a transient power supply rejection ratio, (PSSR) one needs to know the load regulation error, and attenuation of spectrum in supply for conducted noise and amount of crosstalk and where the ingress points are for radiated noise. (RF Current loops and voltage coupling capacitance.)
Testing for radiated ingress into a Tx requires testing, such as a relay coil back EMF current loop as a radiator antenna loop with a suitable circuit such as a contacts driving another relay coil open. Dry contact arcs are broadband. Using a small current loop near all power paths aids in locating the high impedance (inductive) points of access.
The Testing for conducted noise interference with current spikes can be done with a large low ESR cap load to coax and charge discharge to battery voltage. I=V/CapESR. While attenuation in TX supply is measured AC coupled to coax into a 50 Ohm load at DSO using a BNC T to insert 50 ohm R.
BW differences in the TX channel also make a difference in how much energy of the broadband pulse spike is attenuated.
Once you know how noise ingress is injected (conducted and/or radiated) and where it is most sensitive, the solution becomes easier to solve.
The change from copper to carbon (50kohm) ignition wires to reduce sparkplug current was the biggest source of improvement in the last century for automotive noise. But I recall battery rejuvenators with low power high energy pulses across batteries to restore ESR of truck batteries also interfered with truck drivers ability to pickup weak AM or CB signals on the road when they used sparkless diesel engines.
