Business segment information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 27, 2014	Jun. 28, 2013	Jun. 27, 2014	Jun. 28, 2013
Segment Reporting Information [Line Items]
Net sales	$ 93,567	$ 88,258	$ 175,219	$ 173,064
Operating profit (loss) excluding severance, impairment and other associated costs, and legal reserve costs	2,711	1,742	2,315	2,749
Severance, impairment and other associated costs	976	93	1,937	112
Legal reserve	11	37	22	75
Operating profit	1,724	1,612	356	2,562
Interest expense, net	(6,361)	(6,774)	(13,479)	(11,888)
Other income (expense), net	318	(408)	245	(2,940)
Loss before income taxes	(4,319)	(5,570)	(12,878)	(12,266)
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Severance, impairment and other associated costs	976	93	1,937	112
Legal reserve	11	37	22	75
Network [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	42,157	38,454	77,099	74,285
Operating profit (loss) excluding severance, impairment and other associated costs, and legal reserve costs	2,078	922	3,009	2,254
Power [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	28,086	29,554	54,573	57,139
Operating profit (loss) excluding severance, impairment and other associated costs, and legal reserve costs	2,195	1,910	3,512	3,079
Wireless [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	23,324	20,250	43,547	41,640
Operating profit (loss) excluding severance, impairment and other associated costs, and legal reserve costs	$ (1,562)	$ (1,090)	$ (4,206)	$ (2,584)