Planning a simple RF Distribution System

[Terry]

Unfortunately, Trevor, there is no specification so there is no way of knowing what its signal handling properties are.

What is the maximum output? I assume it is intended as low noise pre-amp of some kind. The possibility of getting a usable output at the kind of level you would be looking for could well result in 99% distortion products and 1% signal!

You need to look a bit deeper into this - if you can find a detailed specification, we could look into it further.

[Murphyv310]

Thanks Terry.
I'll try and do some digging over the next couple of days.

[Murphyv310]

Hi.
I got about 45 minutes today to play around with the little LNA amplifiers. Firstly I took the output from my three Auroras and fed them to a little centre loaded aerial and placed this on the bench I then switched on one of my TV9-90 TV's, it lost its road aerial years ago and has a flying coax with a plug on it, with no aerial there was weak sound on CH1 & 2 and a barely locked picture on CH9. Adding in the LNA and to the same aerial CH1 & 2 gives a reasonable picture and CH9 totally noise free. There was no crossmod or any other issues, one or two harmonics though.
I then tried the Hedghog on CH9, again really good also on CH1 with good results, mind there is no filtering after it so the LNA is taking full signal, on my 10Mhz Hitachi Scope there was 2v p-p on the RF output on CH1. I'd suspect they could be used for a decent sized aerial distribution system. No doubt filtering would be beneficial and some more tests on a technical basis.

               

[ppppenguin]

Just to make this clear, the LNA is amplifying the Aurora or Hedghog output. Not as a preamp for the TV.

It would be interesting to see what happens if you combine 2 or more signals into the LNA. Especially if you can view the result on a spectrum analyser. That would really test the linearity with large signals. If you wanted to make a larger distrubition system with these LNAs then they're cheap enough to consider using one per channel with combining at high level. That would certainly keep crossmod under control. Though a LPF between the modulator and LNA would always be a good idea. The harmonics from an Aurora or Hedghog are truly horrible, espcially in Band I.

[Murphyv310]

Hi Jeffrey.
As you correctly say it is amplifying the output from the Aurora or Hedghog, lust like a little linear amp.
There is enough signal to run the sets with either no aerial connected or a wet string in the aerial socket. I'll post up the spec in a few minutes.


Size: 25 * 52 mm
Diameter of end: 5 mm
Operating frequency: 0.1 - 2000 MHz
Amplifier gain:
F = 0.1 MHz, gain = 32dB
F = 500 MHz, gain = 31dB
F = 1000 MHz, gain = 29dB
F = 1500Mhz, gain = 25dB
F = 2000 MHz, gain = 20dB
Maximum power output: + 10dBm (10mW) @ 1dB Compression point
Power supply voltage: 6-12 VDC
System impedance: 50 Ω



1. When working frequency is less than 500 MHZ, it get well gain flatness, can make it less than 1dB after careful adjustment.
The lower frequency the higher gain consistency.
2.amplifier working frequency of the lower limit is subject to input and output capacitor, the default value is 0.1 uF, working to 0.1 MHz.
Increase the input and output capacitance appropriately, can extend the cut-off frequency, such as 10uF capacitance can work to 5 kHz.
3. When the power supply voltage changes in 5-8 v, it can be used as a variable gain amplifier,
gain increases with the increase of the power supply voltage, which receive suitable for radio frequency front-end circuit,
using from control power supply voltage, to control the gain of the amplifier, automatic gain control
4. When the power supply voltage in the 8-10 v, the low frequency end gain up to 30 db,
at this time the amplifier has a low noise coefficient and good stability.
5. when the voltage is 12 v, reach maximum gain, the low frequency end gain of 32.5 DB.

The above is the blurb on E-bay, Bang good & Ali-express

[Murphyv310]

It would be interesting to see what happens if you combine 2 or more signals into the LNA. Especially if you can view the result on a spectrum analyser. That would really test the linearity with large signals. If you wanted to make a larger distrubition system with these LNAs then they're cheap enough to consider using one per channel with combining at high level. That would certainly keep crossmod under control. Though a LPF between the modulator and LNA would always be a good idea. The harmonics from an Aurora or Hedghog are truly horrible, espcially in Band I.

Hi Jeffrey.
Indeed I did have three channels fed into the LNA with excellent results on screen, there were certainly plenty of harmonics well up into UHF, of course these are seen directly off my three auroras but at a much lower level. If I can suitably attenuate the output of the LNA I can view the harmonics on a spectrum analyser program I have for the SdrPlay RSP1A, all dependent on time though.

[Murphyv310]

Confession time!!!!
I was able to snatch about 40 minutes this afternoon. I connected the LNA to the Hedghog and fed its output on channel 9 to a 10 Element Wideband, Band 3 aerial vertically polarised at about 5 feet high from the ground outside of the shed.
I took the best Sony 9-90 into the kitchen which is about 10 meters from the aerial, the result was very strong indeed with no noise, moving the rod resulted in overloading. I then asked my neighbour across the road if I could test it in her home, 30 meters from the aerial and in the correct direction, still superb pictures and sound.
I then had to pop out for Anne who is still in bed unwell. I took the set and at the Tesco Car park there was still noise free reception, its about 800 meters from home as the crow or RF flies!! I then drove up to a car park right at the the top of the town which is 1.2 miles away so a direct mile I'd say, the picture was still good with just a hint of noise, this was using the Sony rod aerial and inside the car!
I drove home and pulled the plug. Just shows what 10 Milli Watts and a directional aerial can do, it just make me wonder how far it may have gone??
Thank you father for hearing my confession. I promise I wont do it again.... honest.
   

[ppppenguin]

We'll visit you in Barlinnie

[Murphyv310]

Thanks Jeffrey. At least they've got proper bogs now!
I suppose I should hand in my £3:50 LNA?

[ppppenguin]

I don't think the power is quite 10mW. The Aurora or Hedghog delivers about 18mV into 75R. About 4uW. So 30dB gain gives about 4mW. This also ignores the 75R to 50R mismatch.

For Ch1 a simple 3 pole Butterworth filter would do a lot of good with the harmonics. At 75R the components for 3dB down at 60MHz are approximately a pair of 33p caps and a 0.4uH inductor. The attenuation at 135MHz (3rd harmonic) would just over 20dB. Higher harmonics would be a long way down. The deisgn could be tweaked slightly to do the 75R to 50R match.