Where do you want the LEDs, at the preamp, at the power supply, or somewhere in between?

Good Question. My setup is OTA only. Two outdoor antennas. I have a couple weatherproof gray boxes at the bottom of each antenna mast, and would like to have the LEDs at that point. That's about halfway between the preamp(s) and the power supply(s). Mostly I want these so when I'm not home and the TV goes out, I can do some PD over the phone with the wife, who will be in a panic without TV (it has happened before)! :rolleyes:

I originally wanted to put the LED(s) into the CM777 preamps, with LED facing down. But without a schematic, I would probably toast the unit while experimenting.

You might need a small RF choke between the center conductor and the resistor to keep the RF isolated from the LED circuit.

Good idea. Any guess as to what choke value I should be looking for?

Thanks,

Bobby

LED simply connects (in series with choke) between center wire and shield of down-lead coax.

Choke reactance should be more than say 10 x 75-ohms (about 1000-ohms) for lowest frequency of interest:
http://www.midnightscience.com/formulas-calculators.html#formulas2
This will ensure that the LED's internal RF impedance doesn't short out the desired RF signal.

LED simply connects (in series with choke) between center wire and shield of down-lead coax.Correct me if I'm wrong, but I think you also need a resistor of at least 1200 ohms in that series string to limit the LED current. The power supply has to supply current to the preamp AND the LED.

Center conductor > choke > resistor > LED > coax shield

Some preamp power injectors also connect a capacitor to ground on the DC side of the choke to keep the RF out of the power supply, but I don't think you need that for this application.

The electrical properties of chokes and capacitors make it possible for the RF signals and the DC power for the preamp to share the coax downlead. The RF and DC are separated at each end because chokes pass DC but block RF; capacitors pass RF but block DC.

I don't have a diagram of the CM power supply, but the attachment shows the diagram of an RS 15-1115 preamp and power supply. CH1 passes DC, but blocks RF. C4 passes RF but blocks DC. C5 shorts any RF that gets through the choke to ground to keep it out of the DC power supply.

An RS Catalog # 273-102, 100 µH RF Choke might be suitable.

I don't really see the benefit of an LED indicator on a power inserter. It's easy enough to determine if an active element of your system has failed.

Easy for Bobby, but not his wife.

Mostly I want these so when I'm not home and the TV goes out, I can do some PD over the phone with the wife, who will be in a panic without TV (it has happened before)! :rolleyes:I think you would be wise to setup an independent backup system so that your wife would at least be able to watch a few strong signals until you were able to repair the primary system.

In my case, I needed to setup an OTA antenna and a battery operated TV to be able to get a few channels during a power failure or cable outage to make my wife happy. Since she would benefit from the backup system, she was very gracious about the extra expense and time that I spent on the project.

I think you would be wise to setup an independent backup system so that your wife would at least be able to watch a few strong signals until you were able to repair the primary system.

That is on my to-do list. I have an extra mast (aside from the main antennas) that I use for experimenting. I'll probably set that up as a backup that she can switch to when the main systems fails.

Thanks for all the replies! This is a great forum!

Bobby

I was trying to avoid the subject of how to connect an LED, knowing full well that LEDs can come as "bare diodes",
meaning they usually need either a series resistor, or better, an "LED Driver" IC to provide constant current or they
can come with one or the other of the above built into the LED and are specified to operate over a particular range
of voltages.....

Good point; you are correct.

I also saw that I needed to expand my explanation for Bobby.

Wow I went back to the last page to figure out why do we want an LED? We should worry about Jack & Jill and intermodulation. My advice; keep a dictionary handy while at this site. Forget the LED the LCD will tell U anyway.

We should worry about Jack & Jill and intermodulation. My advice; keep a dictionary handy while at this site.
Lol, awesome. I agree, just educate the wife. Or use a Winegard preamp which already has the LED.

Speaking of Jack & Jill...
Found this cgi script.
Looks useful for lookin at cascaded systems in terms of both Noise Figure, and iip3 of components...
For a complete story.

http://rfcascade.sourceforge.net/cgi-bin/cascade.cgi

Threw together the below input to represent typical components of an OTA Antenna system.
Very simple to re-arrange / modify components of an installation.
For example, to watch Jack & Jill climb the hill, keep raising the input signal level (source c) in say 10 dB steps and check the
3rd Order IM level, in dBc at the tuner after each run to see the potential impact from
stronger signals.
More details if ya follow the main link and read the manual.

defaults rin=75 rout=75 rho=0
source c=-80 cn=20 bw=6e6
balun+jmpr g=-2 nf=2 iip3=0 rin=300 rout=75
pre-amp g=19 nf=2.7 iip3=-22.3
downlead_coax g=-2.7 nf=2.7 iip3=0
4way_splitter g=-7 nf=7 iip3=0
drop_coax g=-1.3 nf=1.3 iip3=0
tuner g=10 nf=7.2 iip3=-10

More better?? so ya can follow the IP3 thru the stages, set the passive components to a ridiculously high iip3, since it's mainly the active
components contributing anyway.

defaults rin=75 rout=75 rho=0
source c=-80 cn=20 bw=6e6
balun+jmpr g=-2 nf=2 iip3=100 rin=300 rout=75
pre-amp g=19 nf=2.7 iip3=-22.3
downlead_coax g=-2.7 nf=2.7 iip3=100
4way_splitter g=-7 nf=7 iip3=100
drop_coax g=-1.3 nf=1.3 iip3=100
tuner g=10 nf=7.2 iip3=-10

Hello all,

I've just moved, and setup my CM4228HD and 7777 preamp up on the balcony, expecting that I'd get way better results than when I was on the ground. (I've moved about 300 feet down the street)

My reception stinks (practically non existant), and have been puttering around trying to figure out why.. Well, I discovered that when I unplug the TV out cable from the CM supply leading to the tuner (at the power supply end) and barely touch the conductor to the outlet on the PS my signal jumps to where reception is where it should be. Plugging it into the box properly or even partially, it drops out again. I basically have to rest it against the threads of the connector.

Short circuit inside the connector on the PS box? Or something else entirely that may be escaping me?

Do you have another cable you could try? There might be a short in the one you're using.

Yup, that was the first thing I tried, same result. Maybe I'll find a 3rd; with my luck I've got two garbage ones on my hands :)

They're both good RG6 ones though; that I was using before.

I basically have to rest it against the threads of the connector.Do you mean rest the core conductor wire against the threads, or the outer threaded connector against it?

I have to rest the core against the outer threads. Touching it barely inside the hole sort of works; but not really, and I was probably coming into contact with the outer threads doing that anyhow.

Edit: Problem solved. I guess being 6 floors up improved the signals so much I was overloading everything (though the only stations that came in were the strongest ones, when the cable was properly connected...the weaker ones were all dead). I bought a variable attenuator when I bought the amp just in case I did overload, and never needed it. Apparently, now I do. Just putting that inline between the preamp power supply and the tuner, solved the problem.

That's great - please post your TVFool and your own results in your local thread so that others can beware of that overload situation where you are. :)

I'm looking for a low noise mast mounted PREAMP with a high Third Order Intercept that produces about 13 to 18 dB of gain on UHF. The intent is to make up for transmission loss and a 4-way splitter to feed three TV's.

I live just north of Toronto in Nobleton. The CN TWR is only a few degree's east of the Buffalo azimuth. Using an old fashioned VHF/UHF head, my best performance is when aiming the antenna approximately at St. Catherines. This seems to be the best compromise for the "near/far" overload effect.

With no preamp and only 1 TV connected, I receive 18 stations (not counting the additional programs). The Sony display's SNR indicating 26 (religious) is on the edge at 17 db, so it is the first to go when I use a 2-way splitter. ION comes sporadically but is not reliable. No WNGS and it is understood that a preamp cannot help if there is no signal to raise from the dead. Other than during thermal inversions, most stations, including the big Buffalo networks, have consistent/stable signals.

I've now experimented with three different preamps, all of which have failed.

A Radio Shack preamp seemed to work OK in the summer. Wasn't perfect since the 3.5dB NF would negate any signal advantage. Mysteriously I'd loose weak stations when very cold outside in winter. Seems the FM trap is only effective in upper half of the FM band. So the lower half of FM and CH5 analog (-15dBm) would overload my TV's (4-way splitter applied). I tested this thing using a spec a with tracking generator while the preamp was frozen in a freezer and didn't see any temperature instability.

I purchased the Kitz KT-200 that boasts a 36 dBm TOI, but again...way too much gain. Since this preamp has no front end filtering, it isn't surprising that with my VHF/FM/UHF head, its output clobered my TV's no matter what attenuation I put between the preamp and the TV. Perhaps this amplifier will work with with a UHF only antenna that would naturally limit VHF signal strength?

Since it was inexpensive, I purchased an Antra PAU18. It is UHF only. On the tracking generator, the gain drops off rapidly below 450 MHz. By 300MHz, the gain is down >50dB. It claims 2 dB NF and 28dB gain... way too much gain for me. The results were IMD up and down the entire spectrum from DC to daylight! All HDTV stations consistently reported 10dB worse SNR than with no preamp. The TV's AGC was pegged on most of the stations.

Any suggestions for a desirable preamp for this application? I'm ready to do some surgery and perhaps take the Antra apart and transplant the filter into the KT-200? Or I wait until analog is shut down later this year. The spectrum may be a bit easier to deal with.

For discussion.... ;)