balm,

If I'm reading this right, it means you can't use a 'dc block' type attentuator in between a preamp and the power supply ?

it means you can't use a 'dc block' type attentuator in between a preamp and the power supply ?
Exactly. "DC" refers to (nearly all) pre-amp power supplies here, and if the attenuator blocks the DC, then your pre-amp won't work.

-ml

whats the advantage for summit source to sell only DC block, I assume they are cheaper?

whats the advantage for summit source to sell only DC block, I assume they are cheaper?
No advantage nor disadvantage.

I imagine that DC-block is a simpler design than non-DC block..

To pass DC, there pretty much has to be a zero-ohm straight-thru wire in a device. That makes it somewhat difficult to attenuate RF at the same time. Not impossible, just more complex.

Cheers

so far online I only found the DC block, or not specified, can I just use these between the power supply and tv just as effectively as using a power-pass one anywhere else in the line...

thanks

Yup....

Question: If it's a case of a preamp overload.

If you are really close to a broadcast tower, would it make more sense to attenuate before the preamp at the antenna or after the preamp's power supply.

Keep in mind that the variable attenuators should be considers as "not passing DC power". All this really means is you can't put them in a line that is carrying pre-amp power (between the power inserter and the amplifier). This would be an undesirable position anyway so it shouldn't matter.

I have an RS attenuator that was in my "junk" box for many years. I don't even know when I got it, it's been so long. It still works great!

FWIW, the attenuator from A-D is a bit of an anomoly. It appears that, with the knob fully CCW, it exhibits about 25 dB of attuation. With the knob fully CW, the attenuation drops to about 6 dB but no lower. It seems to work "backwards" and isn't actually a 0-20 dB attenuator rather a 6-25 dB attenuator.

so basically, as I see it, "power pass" attenuators dont even exist for average consumer level..

Question: If it's a case of a preamp overload.

If you are really close to a broadcast tower, would it make more sense to attenuate before the preamp at the antenna or after the preamp's power supply.

I wouldn't put an attenuator before the pre-amp as it will push your weak signals down into the noise floor and make them un-receivable. If you have one or two channels that are causing the pre-amp to overload (and you are sure it is the pre-amp that is overloading) you could use notch filters to attenuate those strong signals while not significantly affecting the weak ones. If possible though, it would be better to use a pre-amp that doesn't overload and put the filters after it, as they will have a small effect on the weak signal and when it comes to weak signals, every bit counts.

Does anyone make channel specific notch filters that are not too expensive?

"power pass" attenuators dont even exist for average consumer levelThe attenuator I photographed for Post #14 of the OTA FAQ allows DC Power Pass and was bought at The Source for less than $10, so keep that in mind.

I've thought about making my own for quite some time but I'd also be concerned about the shielding. Has anyone ever opened the case on any of them to get the part numbers and values from off the pots?

Using roger1818's table in Post #866 it would similarly be possible to breadboard a switching network with 1dB granularity for attenuation testing.

Question: If it's a case of a preamp overload.

If you are really close to a broadcast tower, would it make more sense to attenuate before the preamp at the antenna or after the preamp's power supply.

I wouldn't put an attenuator before the pre-amp as it will push your weak signals down into the noise floor and make them un-receivable. If you have one or two channels that are causing the pre-amp to overload (and you are sure it is the pre-amp that is overloading) you could use notch filters to attenuate those strong signals while not significantly affecting the weak ones. If possible though, it would be better to use a pre-amp that doesn't overload and put the filters after it, as they will have a small effect on the weak signal and when it comes to weak signals, every bit counts.
The purpose of inserting attenuation is to reduce Third Order Intermod products in an amplifier.
Hence it would have to be inserted on the Preamp's INPUT, reducing IMD by 3 dB for every 1 dB
of extra attenuation. Hence a healthy 9 dB reduction in IMD occurs with only 3 dB attenuation.
Because it is on the Preamp's input, it doesn't matter whether it is DC PASS or not.

In high signal level areas, it is also possible to overload your Tuner (desensitize due to IMD products),
with or without an intervening Preamp/Distro Amp. Again, it wouldn't matter whether the
RF Attenuator was DC PASS or not if inserted directly on the TV's INPUT.

In most situations, the Preamp is the primary problem. You can calculate expected signal levels
at Preamp and DTV input with a simple spread sheet I posted here:
http://imageevent.com/holl_ands/files/ota

Does anyone make channel specific notch filters that are not too expensive?
I would have said the Winegard UT-2700 UHF Signal Trap, but its price has skyrocketed. Besides you then need to find a way to tune it, which can be difficult without proper test equipment. You may be better off getting a Tinlee Notch Trap as they will tune it for you.

Keep in mind that after the analog shutdown you may not need it anymore.

Carefully check to see how much attenuation there is on your DESIRED channels,
cuz the skirts on these "almost affordable" notch filters are quite wide....

The purpose of inserting attenuation is to reduce Third Order Intermod products in an amplifier.
Hence it would have to be inserted on the Preamp's INPUT, reducing IMD by 3 dB for every 1 dB
of extra attenuation. Hence a healthy 9 dB reduction in IMD occurs with only 3 dB attenuation.

I understand what you are saying and this is fine if all of your signals are quite strong to begin with. The problem comes when you also have distant signals you are trying to receive. In that case one or two dB of attenuation before the pre-amp could be lethal.

In the first case, you may not even need a pre-amp as the un-amplified signals may be strong enough to overcome the line and splitter losses (the whole purpose of using a pre-amp is to get the amplifier as close to the antenna as possible to minimize signal loss between the two).

Carefully check to see how much attenuation there is on your DESIRED channels,
cuz the skirts on these "almost affordable" notch filters are quite wide....
Agreed. All but the most expensive ones will knock out adjacent channels and some will also hurt alternate (and possibly 2nd and even 3rd alternate) channels.

stampeder,

thanks for that, unfortunately it seems the Source doesnt carry that anymore, unless its called something else by them :(

Maybe new owner Bell is moving The Source out of the electronics DIYer/hobbyist business once and for all. :eek: Have you checked the usual Montreal suppliers (Raybel, Montcalm, Addison, etc.)?