[resolved ]Re: High Z Antenna Amplifier - intermods


Chris Moulding
 

Hi Nick,

Interesting to hear about your additional common mode filter.

The common mode filter built into the amplifier has around 50 uH inductance from memory.

Your additional choke will certainly stop any noise on LW and MW.

Regards,

Chris


Chris Moulding
 

Hi Nick,

Interesting to hear about your additional common mode filter.

The common mode filter built into the amplifier has around 50 uH inductance from memory.

Your additional choke will certainly stop any noise on LW and MW.

Regards,

Chris


Nick G4IRX
 

Hi Chris,

I've spent some time testing today with a 6m vertical and a ground rod.

Intitially, poor on MW and LW (lots of common-mode pickup due to around 10m of RG174 feeder) but better above 1.5MHz. I found that by adding a substantial common-mode choke at the amplifier I could get rid of this and I can now hear the weaker LW and MW stations, Poland on 225kHz and Spirit Radio in Ireland on 547kHz. Even MSF on 60kHz is a reasonable signal.

The choke I've used is 10 turns of twisted pair on a T37 material Epcos toroid (RS part 125-3316). Inductance of the winding measures approx 750uH.

Regards,
Nick


Chris Moulding
 

Hi Nick,

Good to hear that you found the problem.

Sorry to hear that it's a solder joint.

We use probably the best soldering irons (Metcal), try to follow the NASA specs for soldering and test everything at least twice before it's shipped out and still the odd dry joint slips out!

I think that you will be happy with it when you put your vertical up.

A vertical antenna with a High Z Antenna Amplifier is always my favourite HF antenna in a low noise location.

Regards,

Chris


Nick G4IRX
 

On Sun, Sep 4, 2022 at 08:36 PM, Simon wrote:
Its a good preamp.. ( especially for the £)
Definately. MW and LW now full of big, but clean signals. I've got it hooked up with 6ft of wire conected to my Icom IC-R72 in the shed at present. It's not as quiet in this environment as my LAA+ loop, but then I expected it to pick up all the local electro-smog. Current consumption sems to be around 40mA (but the bias tee draws 10mA with no amp connected). Should run happily for a few hours on a small 12v battery.

Time to go find my stepped attenuator...

73
Nick


Simon
 

Its a good preamp.. ( especially for the £)

Have fun

Simon g0zen


Nick G4IRX
 

Hi Chris,

I cut the jumper but it made no difference.

i then looked inside and found pressing on the amplifier IC resolved the problem. A closer check on the pins showed there was a problem with the joint on the outout pin. I re-flowed th solder on this one then it sprang back to life :) R4 on 198kHz re appeared rather than the intermod from the 999kHz. So I suspect a rusty-bolt type effect causing the problem due to the output pin no making a proper connection with the pad.

I'll give it a through test next week when I put up a vertical.

Regards,
Nick