Hi Bob, Gentlemen,
Basically i am a lazy guy, i.e. i have never relished tuning RF PA input & output circuits to operate on one frequency. In the 1980s i discovered there were wonderful products: Class A linear wideband amplifiers which would amplify from DC to 500 Mhz, 1 GHz or more with no tuning, so i adopted a "black box" gain block approach. Been doing this ever since.
Now Bob, to come back to your question, since your modulators are in the VHF band, an amp with an upper limit of 250 to 300 MHz is all you need. The good news is that these models are also cheaper than the multi-GHz models.
Typical modulators put out a fairly powerful signal to feed a TV antenna input but not enough to efficiently drive an RF Power Amplifier (PA) so you are going to need several gain blocks.
If amplifying from a typical TV modulator (Broadcast quality) i will typically use a first amp with 15-20 dB gain, then another, then a final PA with +27dBm output (1/2 Watts RF) or +30 dBm (1 watt) into 50 Ohms normalized RF Load.
You can browse the E-Bay RF amp section to get an idea of the products available:
http://business.listings.ebay.com/Pa...istingItemList
And if you give me your E-Mail address by PM, i can send you my photo/pdf data sheet library of suitable elements i've built up over time.
i've used a lot of Mini-Circuits products:
http://www.minicircuits.com/
And also Avantek devices, now defunct but readily available in the Used Market, great products with often MIL specs characteristics.
To Phil (Hi Phil! & Best Wishes for 2009)
Ramsey products SUCK!
I built their Ch-6 TV transmitter kit and the performance is abysmally low - avoid at all cost, a total loss of money.
If you want to buy a ready-made GOOD product, try this Greek, yes Greek company. I discovered them 6 years ago, and their transmitters are indisguishable on-screen from regular TV transmissions, and yes the transmitter works in NTSC/3.58/525/60 VHF & UHF - 100 mW RF out
http://www.aspisys.com/tvpll.htm
* i have no ties to the Co.
I should know: I run 40+ 1 inch to 5 inch small-screen TVs (Sony-Panasonic-Sharp) on their whip antennas and the TVs look like they are receiving WABC from across the Atlantic.
Quote:
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Originally Posted by ohohyodafarted
NOTE: Unlicensed broadcast is not legal in the TV band in the US. Low power AM and FM radio-band transmitters are legal and work for some short-range purposes, because the band width is smaller and a radio receiver can get by on lower signals. FM adapters for auxiliary devices in cars (cassette, satellite radio) work this way. Also, the 'Mister Microphone" toy, if you remember that
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OK, i will be blunt: just do it! 35 years of tinkering with AM, FM, TV & Wi-Fi transmissions have taught me that:
- If you don't pollute neighbors reception nor a legit transmitter, "they"
couldn't care less !
Anyway, the FCC is now a shadow of the power they had in the 60s-70s so fight back, feed your vintage TVs with a decent analog signal & Amen.
Best Regards
jhalphen
Paris/France