AVS Forum - View Single Post - Philips DVDR3575H/37 160G HDD DVD Recorder w/ ATSC tuner

wajo · 10-07-07, 02:14 PM

The Philips 3575/3576 "Active" (Amplified) Coax Passthru

I always wondered how much insertion loss there might be in the DVDR/VCR coax passthru connections (RF in/out loop)...knew there was "some" but had no quantifier. (Generally speaking, a good, standard 2-way splitter has a -3.7dB loss on each output, and the loss increases the more outputs you add.)

Here's a test site post where someone actually measured the loss thru a passive VCR RF loop (same as our DVDRs) and found it to be "less than 1dB" (see post by Sofie).

In fact, the post suggests it could be a net gain if the passthru is "active" which just means it has to be plugged in, not on.

It would be good to know if our DVDRs have a passive or active passthru, which would determine whether we are getting less than 1dB loss or possibly getting a net gain in RF signal!

EDIT: Answered my own question...I unplugged the power cord on my Philips 3575, off at the time, and noticed an immediate degradation in picture quality. Plugged back in and perfect pic again, 3575 still off.

If it were a passive passthru, there would be no noticeable difference in PQ. (Did the same test with my Pioneer DVR-640 and it has a passive passthru.)

The 3575's DVDR RF LOOP IS ACTIVE, AND WE'RE GETTING A LOSSLESS PASSTHRU AND PROBABLY A NET GAIN!

The amplification circuit is a 4dB amp > Low-Pass Filter (LPF) > 2dB amp.

Note: My tests were done with the Philips 3575 and the Pio 640 connected directly to a TV...no other boxes or components in between to block or amplify the effect.
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10-07-07, 02:14 PM	#2065 \| Link
wajo AVS Special Member Join Date: Dec 2005 Posts: 8,619	The Philips 3575/3576 "Active" (Amplified) Coax Passthru I always wondered how much insertion loss there might be in the DVDR/VCR coax passthru connections (RF in/out loop)...knew there was "some" but had no quantifier. (Generally speaking, a good, standard 2-way splitter has a -3.7dB loss on each output, and the loss increases the more outputs you add.) Here's a test site post where someone actually measured the loss thru a passive VCR RF loop (same as our DVDRs) and found it to be "less than 1dB" (see post by Sofie). In fact, the post suggests it could be a net gain if the passthru is "active" which just means it has to be plugged in, not on. It would be good to know if our DVDRs have a passive or active passthru, which would determine whether we are getting less than 1dB loss or possibly getting a net gain in RF signal! EDIT: Answered my own question...I unplugged the power cord on my Philips 3575, off at the time, and noticed an immediate degradation in picture quality. Plugged back in and perfect pic again, 3575 still off. If it were a passive passthru, there would be no noticeable difference in PQ. (Did the same test with my Pioneer DVR-640 and it has a passive passthru.) The 3575's DVDR RF LOOP IS ACTIVE, AND WE'RE GETTING A LOSSLESS PASSTHRU AND PROBABLY A NET GAIN! The amplification circuit is a 4dB amp > Low-Pass Filter (LPF) > 2dB amp. Note: My tests were done with the Philips 3575 and the Pio 640 connected directly to a TV...no other boxes or components in between to block or amplify the effect. . Last edited by wajo; 09-12-09 at 04:51 PM..