I'd like to pass along a good tip for HF listeners with cable tv in their home. This tip may or may not apply to you, so I will tell you what my circumstances are.
After having Comcast Cable install their "package" of services:
1. Internet
2. TV channels
3. Cable telephone service
with the "Touchstone" Telephony Modem, I had horrendous noise generated all over the MW-SW bands at my location.
I suspected that this buzz/hash was coming from the new system installed but had to make sure. I also didn't want to modify or remove the equipment and lose the service.
Shutting off everything in the household, and powering it all up one circuit at a time, I found that the modem itself was the culprit. This modem is Touchstone model TM402P. This model has a 120VAC cord that plugs in the back of the unit to power the modem, so the unit has its own built in power supply. It also has an internal Li-Ion battery for backup when the power fails. It will "hold up" the telephone function in case of an outage for a number of hours.
I suspected that the internal power supply was generating the "hash" on HF when the modem was plugged into AC power. My first attempt to kill the interference was to wind the AC cord on a large ferrite toroid, trying to choke off the hash. I thought that the hash was traveling back out the cord and getting into the rest of the household wiring, where it was being radiated all over the home.
BTW, I cannot modify the modem as it is being "rented" from the company... it is theirs, not mine.
This choke failed to give any relief... the noise was still all over the spectrum covered by the HF receiver. I finally came to the realization that I could simply unplug the AC cord for the modem and see what happened. RELIEF!! YES!! The HF interference was nearly all gone, and I could finally copy weaker signals again!
What must be happening is that the internal power supply has little to no filtering, and all the switching transients are polluting the HF spectum household-wide. With no AC input, there is no hash generated. When I listen to my HF radio now, I simply unplug the AC from the modem and let the battery backup take over to keep the telephone working. When I am finished with HF listening, I just plug the cord back in to restore battery charging and normal modem operation.
I still notice some weaker digital noise on some freqs on the receiver. I assume that they will always be there due to the nature of the cable service and some "leakage". I can/must live with it as it isn't too severe... (hey, the wife needs her TV! ;-)
I hope this tip helps other poor souls who have just about given up the hobby in frustration.
After having Comcast Cable install their "package" of services:
1. Internet
2. TV channels
3. Cable telephone service
with the "Touchstone" Telephony Modem, I had horrendous noise generated all over the MW-SW bands at my location.
I suspected that this buzz/hash was coming from the new system installed but had to make sure. I also didn't want to modify or remove the equipment and lose the service.
Shutting off everything in the household, and powering it all up one circuit at a time, I found that the modem itself was the culprit. This modem is Touchstone model TM402P. This model has a 120VAC cord that plugs in the back of the unit to power the modem, so the unit has its own built in power supply. It also has an internal Li-Ion battery for backup when the power fails. It will "hold up" the telephone function in case of an outage for a number of hours.
I suspected that the internal power supply was generating the "hash" on HF when the modem was plugged into AC power. My first attempt to kill the interference was to wind the AC cord on a large ferrite toroid, trying to choke off the hash. I thought that the hash was traveling back out the cord and getting into the rest of the household wiring, where it was being radiated all over the home.
BTW, I cannot modify the modem as it is being "rented" from the company... it is theirs, not mine.
This choke failed to give any relief... the noise was still all over the spectrum covered by the HF receiver. I finally came to the realization that I could simply unplug the AC cord for the modem and see what happened. RELIEF!! YES!! The HF interference was nearly all gone, and I could finally copy weaker signals again!
What must be happening is that the internal power supply has little to no filtering, and all the switching transients are polluting the HF spectum household-wide. With no AC input, there is no hash generated. When I listen to my HF radio now, I simply unplug the AC from the modem and let the battery backup take over to keep the telephone working. When I am finished with HF listening, I just plug the cord back in to restore battery charging and normal modem operation.
I still notice some weaker digital noise on some freqs on the receiver. I assume that they will always be there due to the nature of the cable service and some "leakage". I can/must live with it as it isn't too severe... (hey, the wife needs her TV! ;-)
I hope this tip helps other poor souls who have just about given up the hobby in frustration.
