[rabbit73]

Originally Posted by sl1982

I just got my c5 and got it installed. I was having issues with picking up fox vhf channel 7). I found a local antenna shop and they suggested getting a preamp. Got it installed and all working. The problem is the signal quality on that channel is only around 50% and it cuts in and out. Any ideas? The preamp has a fm trap built in and it doesnt seem to make any difference having it on or off.

Well, at least your getting Fox even if it's not a high quality signal.

Ok, removing the db8e from the equation gives me identical results.

That eliminates the strong UHF signals coming in from the DB8E. The C5 is still picking up UHF signals, but they will be attenuated by the low pass filter in the combiner by 25 to 40 dB before reaching the preamp.

Just ran a test by hooking up the antenna output to my stereo. I am still able to bring in local fm channels crystal clear even with the fm trap on in the preamp. Could this be causing the problem?

That test is inconclusive. You are probably getting some attenuation from the FM filter in the preamp, but it's not going to completely eliminate FM signals. A good FM tuner doesn't need much signal to function.

edit: also interestingly enough while trying to tune in to a detroit fm station I am getting spillover from one of the locals even though they are about 5 MHz apart (turning the trap back on stops this)

That proves the filter is doing some attenuation. Your strongest FM signal is 65 dB stronger than Fox. I suspect that the preamp doesn't like that, and it is creating distortion products that reduce the SNR of Fox which gives you a low Signal Quality reading. You would need test equipment to see exactly what the numbers are, but you can still try a preamp that is more resistant to overload and some different filters.

All FM filters aren't alike; they have different attenuation curves and a HLSJ can also be used as an FM filter. It attenuates all signals below CH7, including the FM band. See attachments 2-4.

I'm wondering if you could go back to your original setup where you were using the preamp for both antennas but insert several filters before the preamp input. That might also be inconclusive if the strong signals were getting into the plastic case of the preamp which would bypass the filters.

Then you could try a preamp with a metal case that is resistant to overload in place of the preamp with the plastic case. You missed the boat on the Juice, but another one might do.

You could also try a preamp in a metal case that is resistant to overload with an FM filter in front of it to amplify just VHF, but you would need a UVSJ that passes DC to the preamp.

Is your coax grounded with a grounding block? That reduces interference and makes filters much more effective.

edit: ok it seems to be worse. Signal quality is around 45 now........It seems as the temperature outside gets warmer throughout the day the signal gets worse.

OTA signals constantly vary in strength, especially non-LOS signals, and are affected by temperature inversions.

Sorry to keep adding stuff on here but I am unsure if this is pertinent information or not.

Keep the ideas coming, one of them might click. It's too soon to give up.

Was this TL;DR?