attenuator for cable tv.

[KD8GFC]

I know this is not ham radio related but there are some smart people lurking on the Zed. Does anyone know were I can buy a Forward Pass attenuator for cable tv ?? I need one that will weaken the downstream but let the upstream pass untouched. I have found standard attenuators but not the forward pass type any help would be great. Thanks

[KA9JLM]

I know this is not ham radio related but there are some smart people lurking on the Zed. Does anyone know were I can buy a Forward Pass attenuator for cable tv ?? I need one that will weaken the downstream but let the upstream pass untouched. I have found standard attenuators but not the forward pass type any help would be great. Thanks

I like the Tru-spec for something that works good for a good price.

http://www.tselectronic.com/shop/pro...uator-Pads/268

These are Return loss 20dB typical.

When you say Forward Pass, are you meaning directional or DC Pass ?

You may be wanting a Directional coupler / Tap.

http://www.mjsales.net/items.asp?Fam...=265&Cat2ID=93

.

[KD8GFC]

What I need is to lower my downstream modem signal without making my upstream signal go higher. I would need a attenuator that only affects the incoming signal and not affect the outgoing or return signal. Thanks for your reply.

[KA9JLM]

What I need is to lower my downstream modem signal without making my upstream signal go higher. I would need a attenuator that only affects the incoming signal and not affect the outgoing or return signal. Thanks for your reply.

The pads for doing that are built into the line amps.

Sounds like the cable company does not have their amps equalized properly. Or maybe you are doing something special ?

If you know the Up / Down frequency of your system then you could build something.

[KD8GFC]

They dont have it balanced right and getting a tech dont seem to do me much good. My down freq is in the 500 mhz band and my up freq is 29.600 mhz and 27.900 mhz. Thats why I thought I could get a attenuator thats lowers signals above 50 mhz but let 50 mhz and below pass. As you can see my internet workes ok but my modem signal stats are borderline high on the down if they change much more i will have drop outs.

[KA9JLM]

They dont have it balanced right and getting a tech dont seem to do me much good. My down freq is in the 500 mhz band and my up freq is 29.600 mhz and 27.900 mhz. Thats why I thought I could get a attenuator thats lowers signals above 50 mhz but let 50 mhz and below pass. As you can see my internet workes ok but my modem signal stats are borderline high on the down if they change much more i will have drop outs.

You may be able to use a piece of cheap coax and let the frequency Roll off work for that purpose.

Or build a simple low pass filter, that will roll off the highs to meet your requirements.

Do you have a way to measure the signal levels ?
.

[KD8GFC]

Sure do right from the modem itself my down is 9.1 dbmv snr is 40, up is 46 dbmv snr 32 the up is perfect but the down should be from -5 to +8 max dbmv all the snr's are good.

[KD8GFC]

Here are the exact numbers from the Modem...

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 8 597000000 Hz 9.1 dBmV 40.3 dBmV 0 0
2 Locked QAM256 1 555000000 Hz 8.6 dBmV 39.8 dBmV 0 0
3 Locked QAM256 2 561000000 Hz 9.0 dBmV 40.3 dBmV 0 0
4 Locked QAM256 3 567000000 Hz 9.0 dBmV 40.3 dBmV 0 0
5 Locked QAM256 4 573000000 Hz 8.8 dBmV 40.8 dBmV 0 0
6 Locked QAM256 5 579000000 Hz 9.2 dBmV 40.8 dBmV 0 0
7 Locked QAM256 6 585000000 Hz 9.0 dBmV 40.8 dBmV 0 0
8 Locked QAM256 7 591000000 Hz 8.9 dBmV 40.9 dBmV 0 0

Total Correctables Total Uncorrectables
0 0


Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 8 5120 Ksym/sec 27900000 Hz 45.8 dBmV

[KO6WB]

The lowpass filters to eliminate TVI from amateur transmitters does exactly that. The values may need to be played with and of course you can make it much smaller. Look in some of the older Handbooks that have different impedance.
Good luck
73
Gary

[KA9JLM]

It sounds like you are within target according to this;

Downstream Received Power: the DOCSIS specification requires cable modems to function correctly with downstream power levels in the range -15 dBmV to +15 dBmV: power readings at or close to those extremes are likely to be unacceptable. However, when connected to a real-life CATV network, a cable modem might be functional over a narrower range than this. Accordingly, cable ISPs will specify an even narrower target range when commissioning their network: this target range will differ according to ISP.

http://homepage.ntlworld.com/robin.d...ps/signal.html