Hi,

I recently purchased a Blonder Tongue TV modulator from ebay. These devices are meant to be used in schools/hospitals/hotels where they need to transmit information on a certain TV channel. The transmitter can transmit on all VHF channels and almost all UHF with a maximum of about 40mW output power.

I have one of those mitsubishi modules 30W, that works across 50-90MHz, so it is perfect for VHF low transmission. I tested it with this as well as some lower power MMIC type amplifiers and it seems to work OK, but it creates a mirror of the audio carrier on the low side of the video carrier. There are only two carriers when hooked up without any amplifier, but through any amplifier, however, it creates this mirror.

Why is this happening? Could this be because it needs a linear amp, and these FM amps aren't linear?
Could it be because the output impedance of the transmitter is 75 ohms, while the coax/amps are all 50 ohms? Maybe I need an impedance transformer?

can you post some picture because i was in need to amply a ch36 uhf old vcr modulator
the shadow come because u need a notch filter that i am not expert in this so other members here can explain better then me good luck but please post some picture to get inspired .

I will post when I get the chance, but it is a very simple amplifier consisting of a mitsubishi module ra30h0608. That might not be the exact number. I don't remember. For your application on ch 36 though, the max frequency these modules come in is 520mhz. I looked at ch 36 and the freq is around 590-600mhz, so it might work, just not as much output, not sure. If the signal is from a vcr then you will need a preamp. MMIC PHA-1+ is a good one.

So anyway, i need a notch filter?
Does anyone know why?