DG8 Pre-Amp - More gain, really?

Well,

I ordered a DG8 pre-amp for 2M from here last week and it duly arrived. I only ordered the "short" kit as I thought I would probably have a lot of the more common bits needed anyhow.

Here's the completed project:

Here's a close up of some of the surface mount gubbins on the other side of the PCB:

And here's my bench after I had built it - a complete disaster area:

I aligned the pre-amp in accordance with the instructions using a SSB RX but thought the results were quite noisy; I then used the tracking generator and the Spectrum Analyser to align, here's the unit in bypass:

The markers are at 144, 145 and 146 Mhz, here's the aligned version:

I backed the gain off as per the instructions and used my ears to adjust L1, still seems noisy to me.

May have to fiddle some more.the IC-9100 used for my new satellite station can power the pre-amp straight down the coax.

I'm planning to run the amp under the radio bench initially; there's not a very long run of coax to the antenna so I am not sure there is that much to be gained by mast mounting it. Let's see.

Here's Miss Luna Cat, I'm rather hoping she doesn't decide to play "shelf swat" with my Nixie Clock!

Local conditions.

Doppler, Frequency Inversion, What's all that then?

Well,

As I fiddle, I learn. That's the basic idea anyhow.

So, I've been making a few QSOs through these amateur satellite thingamagigs.

There are a series of Japanese birds called the XW-2 series. Their frequency allocation is as follows:

Now, the number on the far left top of that image is wrong and should read 435.000.

I just had a QSO through XW-2C, the linear transponder (the bit that receives speech on the uplink and re-transmits it on the downlink) are actualy at the following frequency ranges:

Uplink:       435,150 -> 435,170
Downlink:  145,815 -> 145,795

Now, the observant amongst you will note that the Downlink frequency I have listed goes from high to low and the Uplink from low to high. Thats because it's a linear transponder with Spectrum Inversion. So as I tune in the 20KHz passband of the satellite I have to tune +ve in the Uplink and -ve in the downlink (or the other way round).

So when the Uplink is at 435,150, the Downlink is at 145, 815 and when Up is at 435,170 Down is at 145,795. Thats all before you add in the complexity that the Uplink is in LSB and the Downlink in USB. And then theres the further complexity of Doppler.

Now, I like to think of things very simply. If you can imagine a Sine Wave shape, with the right hand end fixed and the left hand end moving left, it is quite easy to see that the frequency is being stretched and is therefore decreasing. Similarly, if the left hand end of our imaginary sine wave was being moved to the right, the wave is being squashed and the frequency is increasing.

Therefore as the fixed point (my antenna) and the satellite (moving) get closer together the frequency that I need to tune to receive the Downlink and transmit to find the Uplink are both increasing, similarly when the bird is travelling away from me, the frequency is decreasing. The effect of this change is dependent on the actual frequency itself, so the higher the frequency the more pronounced the shift needed.

Luckily the Sat32PC software calculates the Doppler for me, but I hope the rather simplified explanation above helps explain whats actually going on.

Fun egh?

QED on the Birds!

Well,

Following my last post here, I've managed to complete my first Satellite QSO.

I'm using SatPC32 to control the antennas and also the Radio:

My first QSO was with RN6MA in LN06uo - Thanks Victor!

We were using the XW-2A satellite; uplink on 435 MHz and downlink on 145 MHz.

So much to learn!

Here's a video of the antennas in action:

And here a quick video of the IC-9100 receiving the telemetary beacon from XW-2A showing the auto doppler tuning.

Here's Florrie the Ham cat enjoying some sunshine:

Local conditions.