Sierra 24 pilot reported a near midair collision and aircraft equipment problems.

Attributes
ACN	1516248
Time
Date	201801
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Sierra 24
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	VFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	Transponder
Person 1
Function	Single Pilot
Qualification	Flight Crew Instrument Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 71 Flight Crew Total 1800 Flight Crew Type 13
Events
Anomaly	ATC Issue All Types Aircraft Equipment Problem Less Severe Conflict NMAC
Miss Distance	Horizontal 0 Vertical 300

Narrative:

I was ferrying the airplane. The airplane didn't have a very strong transmitter and multiple attempts along the trip to receive flight following proved unsuccessful. I was tuned into unicom for airports I was flying by along my trip. I had just passed ZZZ. As I had just passed it I checked my foreflight to check how I was along my path; and noticed according to the stratus and adsb there was traffic slightly above me; descending directly towards me. I began looking for the airplane. The visibility out of my aircraft is extremely limited. Finally I spotted the traffic about two miles directly ahead; and initiated a rapid climb to avoid the traffic. I then was able to get a hold of ATC center and alert them to a near collision I had with the traffic. They then gave me a squawk code; and noticed my transponder (in certification) was displaying 14;500; even though I was at 7500. Recycled my transponder and it indicated the proper altitude. Shortly after I lost radio contact with ATC and continued to my destination with no further incident.

Original NASA ASRS Text

Title: Sierra 24 pilot reported a NMAC and aircraft equipment problems.

Narrative: I was ferrying the airplane. The airplane didn't have a very strong transmitter and multiple attempts along the trip to receive flight following proved unsuccessful. I was tuned into UNICOM for airports I was flying by along my trip. I had just passed ZZZ. As I had just passed it I checked my ForeFlight to check how I was along my path; and noticed according to the stratus and ADSB there was traffic slightly above me; descending directly towards me. I began looking for the airplane. The visibility out of my aircraft is extremely limited. Finally I spotted the traffic about two miles directly ahead; and initiated a rapid climb to avoid the traffic. I then was able to get a hold of ATC center and alert them to a near collision I had with the traffic. They then gave me a squawk code; and noticed my Transponder (in certification) was displaying 14;500; even though I was at 7500. Recycled my transponder and it indicated the proper altitude. Shortly after I lost radio contact with ATC and continued to my destination with no further incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.