Specific amp question..

[dave3825]

I have a question and figured I would try here. I have been using this amp on my scanner with amazing results. My question is, what exactly does 5-42 MHz Rtn (-1db) mean? As seen on the amp..

 

[prcguy]

In a cable system where a receiver or modem needs to communicate back to the head end, the return allows the device in your house to send signals backward through the amp with little loss.

Basically the amplifier side from input connector to output connector has a high pass filter and the return path has a low pass filter that lets signals below 42MHz go around the amp from the output connector to the input connector.
prcguy

 

[n5ims]

Most often this is for the cable modem's link from your house to the cable company. Since the signal from the modem is relatively low power (compared to the signal from the cable company to your house) the amount of loss in this range is quite important (especially when any loss near the modem is compounded greatly by the loss from the coax in the cable system).

HowStuffWorks "How Cable Modems Work"

 

[dave3825]

Ok that makes sense. So in the scanner world, does it mean it will only have a 15 db gain in the 52 - 1000MHz range and a -1db gain in the 5 - 42MHz range or is the 5 - 42Mhz only used for upstream?

 

[prcguy]

That's what it means but the -1dB is usually expressed as loss, not gain.

Signals within a cable system are very specific with known levels and your amp is designed to live in that environment. A preamp connected to an outside antenna is a different story and the amount of carriers and levels can be great enough to overload the preamp and create IMD, or a host of new interfering frequencies and seriously raise the noise floor covering up things you want to hear.

There are other specs to consider but for a cable TV type preamp connected to an antenna I think 15dB gain is about the most you want to introduce in the system and more will only get you closer to trouble.
prcguy

Ok that makes sense. So in the scanner world, does it mean it will only have a 15 db gain in the 52 - 1000MHz range and a -1db gain in the 5 - 42MHz range or is the 5 - 42Mhz only used for upstream?

 

[WayneH]

Ok that makes sense. So in the scanner world, does it mean it will only have a 15 db gain in the 52 - 1000MHz range and a -1db gain in the 5 - 42MHz range or is the 5 - 42Mhz only used for upstream?

Normally with a CATV amp that supports return you'll have very poor coverage below 50MHz. CATV passive devices (non-amplified) are a non-issue.

I use both a Stridsberg and an 8 port drop-amp and the Stridsberg is worth the extra cost. I've even noticed better accuracy in control channel decoding with a Stridsberg over the drop-amp.