Simple VHF Amplifier??

[ronv]

My friend is trying to build a small television transmitter for his private island (wink wink). The objective would be to power up a satellite receiver output and re-transmit on Chan 3 or 4 at 5 watts or so. Broadband preamps to get from a few milliwatts to 200 milliwatts seem easy enough (no special coils or tuning). We have been looking at circuits using 2SC1971 but all will be difficult for him to tune because he has no special equipment (SWR meter etc.) Any Ideas?

 

[Mikebits]

I made a Amp to retransmit the output of my cable box. It worked well on chan 3. I used a Mini circuit monolithic amp. The amp can output +18 dBm and has a gain around 20dB. Input level to amp should be around -3 to 0dBm. You could always cascade two amp if you need more gain, but I have not tried that. Link to data sheet.

PS. You might want to use a LPF on the output to minimize spurious emissions.
http://www.calculatoredge.com/electronics/ch pi low pass.htm

 

[RadioRon]

If he has no equipment, maybe something like this is in order:
High gain 12W 55-88MHz Band I TV pallet
or this one: TVMAX2000+ 5W VHF TV transmitter with optional stereo sound

 

[ronv]

The ERA5 looks like as simple as you can get. Do you have a source? My friend is in Pakistan and I am in the US.

Ron, Love the ready made solutions but the price is a stopper.

 

[ronv]

Found 5 of them for $15 at my most trusted distributor -- ebay. :+)

 

[Mikebits]

Hold on, just reread your original post. I missed the part where you want 5 watts out. Erm, the amp I suggested is only +18 dBm and 5W is around +37 dBm. Do you really need that much power? Sorry I should have read more carefully.

 

[Mikebits]

This amp will get you 1W output.

 

[ronv]

Thanks,

I think he is looking for a range of about 2KM. It doesn't seem like it would take to much if it is line of site?

 

[small t]

Once my friend used a transmitter module called VMR6512. You can search it from google. Hope it can help you.

 

[Kryten]

Thanks,

I think he is looking for a range of about 2KM. It doesn't seem like it would take to much if it is line of site?

I think 1 W is sufficient for 2 km if the sight line is clear.

Being a HAM i know that you can achieve a great distance with little power. I have done 230 km + with 1.5 watt hand held

 

[RadioRon]

Its all about the antennas, really.
73

 

[ronv]

TV Amp

I'm sure this would be a lot easier if I knew what I was doing. :+)
Here is a circuit I found on the net. I think I have resized the L's and C's to around 66Mhz. and added a low pass filter at 140Mhz. Lots of questions:
1- Did I get the LC's right?
2- Is 140Mhz a good place for the LPF?
3- How is the 2SC1971 biased? Is it class C?
4- I'm not sure of the gain.

Think it will work?

Thanks!

 

[Willen]

This amp will get you 1W output.

This circuit has no detailed description like coil winding details and RFC details. So this is a perfect solution but only fro expert!!! Not to all!! Can anybody provide the details??

 

[Willen]

I think 1 W is sufficient for 2 km if the sight line is clear.

Being a HAM i know that you can achieve a great distance with little power. I have done 230 km + with 1.5 watt hand held

Can you transmitt 230KM using 1.5 watt tx?? What are saying???

 

[Kryten]

Can you transmitt 230KM using 1.5 watt tx?? What are saying???

Yes I opend a repeater that was 230 kM away from me. From what I know there are no hills or anything in the way. I was about 300M above sea level and the repeater is placed rooughtly the same

 

[Willen]

Yes I opend a repeater that was 230 kM away from me. From what I know there are no hills or anything in the way. I was about 300M above sea level and the repeater is placed rooughtly the same

Amazimg!!! Can my 1.5 watt FM Tx at 100MHz transmit 230 KM in your that place/situation?? What is the friquency of your Tx? I think repeater has more sensitivity, and friquency is low, isn't it?

 

[Kryten]

Well I an a Radio Amateur. So tx from is @ 145,650 MHz and ex to me is @ 145,150 MHz

I know that the repeater has good rx sensitivity and have great antennas, I used an antenna with some extra gain (dont know exactly how much)

 

[Willen]

Well I an a Radio Amateur. So tx from is @ 145,650 MHz and ex to me is @ 145,150 MHz

I know that the repeater has good rx sensitivity and have great antennas, I used an antenna with some extra gain (dont know exactly how much)

do you mean 145,650 MHz (145.6GHz? Or MHz?) your Tx has? It's so high friquency! But I think high friquency has short wavelength and generally cannot travel so far, isn't it?
How can you transmit so far using very little powered tx? Can u tell me basic in theroritically? How is it possible to transmit such large distance by 1.5 watt tx? It is so so interesting to me!

 

[Kryten]

It should be 145 point 650 MHz

Im not really sure about the theoretically part of this but it has a lot to do with atmospherically conditions. The different wavelengths travel different in sun and high pressure. (this was done during summer time).
Also I know that higher frequency will travel in a straight line from the transmitting antenna and not bounce in the atmosphere like 1-30 MHz will. And since both me and the repeater was a some height and the signal had optimal conditions it was possible.

In amateur radio we have something called QRP witch is low power operations. These guys actually talk around the world with 1W. It all depends on conditions and antennas.

 

[audioguru]

Guess what?
The world is round, not flat. At a distance of more than about 120km (or less) then the curvature of the world gets in between a transmitter and receiver at these high frequencies.