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Amplifier upgrade - disappointing results


Paul Gulliver
 

Hi Chris,
Received the upgrade kit this morning and carried out the mods.
Unfortunately I'm still not getting good results, attached is the waterfall from the WSJT-X program whilst monitoring FT-8 on 20m.
The bottom section shows the bright colours of strong signals being received with my MLA-30 loop amplifier, the middle blank bit is where I turned off the bias tee and swapped amplifiers and the top section shows the weak signals being received by the CCW amplifier - I even tried to increase the receiver gain within SDR Console to get a stronger signal but this also increase background noise and gave no improvement (I'm using a SDRPlay RSP1A receiver.)

Obviously I may have made some error in the modification but it wasn't that difficult, however I will check in the morning and do some further tests.

I will be interested in seeing the results from other customers - perhaps there is just something about my loop that doesn't suit the CCW amp. (as a reminder it's a 1.1m dia loop from 8mm cu tube)


Paul Newland
 

Dear Paul
Sorry to read that you're still struggling with your CCW loop performance. 
I am pretty much a  novice  with regard to the world of SWL, with exceedingly limited technical skills, from which you obviously do not suffer.
My experience for what it's worth involved a pre-ordered CCW VLF/HF amplifier with a usb powered base unit.
I tried a variety of loops, coax !M aperture (RG58), 90cm hula-loop (using supplied wire), the alloy bike rim and finally a square 1M (15mm copper pipe) version, which was and is the most successful.
Whilst I was pretty satisfied with the VLF performance and LW generally disappointing, shortwave performance being variable using the latter antenna.
As I am totally inept with regard to soldering and don't even understand your "language" of parts, I haven't taken up the Chris's kind offer of upgrade kits, but have, instead bought one of his very good value HF/VHF Bias-T powered amps.
As the Wellbrook handles VLF, LW and Short Wave very well and what I actually wanted the CCW loop for, was to have another loop operating in the HF band, this version certainly does the biz within it's spec, usually equalling or exceeding the performance of the Wellbrook over the same frequency bands, although under some reception conditions this may be reversed.
It also seems to be more directionally sensitive and better at rejecting some spurious signals.
I have both loops mounted quite close together (circumstance), at below 2M above ground level (choice).
I appreciate that this approach may well not appeal to you, but it really is a performer!
Oh yes: Receivers in use are a RSPduo and a RSP2 operated with SDRuno V1.33 Wellbrook on the duo's HiZ port and the CCW on the tuner 2 50 ohm.
Anyway, I look forward to reading of your eventual success with the modificatio/upgrade.

Best Wishes
Paul



On Fri, 17 Jan 2020 at 15:24, Paul Gulliver <paulg1953@...> wrote:
Hi Chris,
Received the upgrade kit this morning and carried out the mods.
Unfortunately I'm still not getting good results, attached is the waterfall from the WSJT-X program whilst monitoring FT-8 on 20m.
The bottom section shows the bright colours of strong signals being received with my MLA-30 loop amplifier, the middle blank bit is where I turned off the bias tee and swapped amplifiers and the top section shows the weak signals being received by the CCW amplifier - I even tried to increase the receiver gain within SDR Console to get a stronger signal but this also increase background noise and gave no improvement (I'm using a SDRPlay RSP1A receiver.)

Obviously I may have made some error in the modification but it wasn't that difficult, however I will check in the morning and do some further tests.

I will be interested in seeing the results from other customers - perhaps there is just something about my loop that doesn't suit the CCW amp. (as a reminder it's a 1.1m dia loop from 8mm cu tube)


Chris Moulding
 

Hi Paul G,

Can you check the coax cable you have running between the head unit and the base unit?

You should be seeing far higher signal levels and I suspect that if one of the centre conductors or shields is open circuit then what you are seeing is picked up by the coax rather than the loop and head unit amplifier.

If you have a voltmeter to hand try measuring the voltage drop across the large 15 ohm resistor (marked 150 or 15R0) on the base unit. It should read some voltage across it if current is flowing through it. If it reads nearly 5V then the coax has a short circuit. If there is no voltage dropped across the resistor then the coax cable is open circuit.

Let me know what you find.

Regards,

Chris


Paul Gulliver
 

Hi Chris,

First the voltage, it's showing 0.53v across the 15 ohm resistor.

I use the same co-ax feed for both amplifiers during the test so if there is a problem for one amp it should be the same for both - the only minor difference is for your amp I use an F socket to BNC adaptor as I have standardised in using F connectors where possible which suits my L band and C band setup.

Regarding pickup in the co-ax, I tried this on Shannon Volmet (5505KHz) and I was receiving a strong signal with the amp connected but it virtually disappeared with the head unit disconnected.

Just done a very quick test on 14074KHz (FT8) - with your amp connected very weak signals coming in but changing over to the MLA-30 amp increased the signal strength significantly - I didn't actually do any decoding, time is a bit short this morning.

Out for the rest of the day so any further tests will have to wait until tomorrow or Monday

Cheers.

Paul


On 17/01/2020 at 20:45, Chris Moulding <chrism@...> wrote:
Hi Paul G,

Can you check the coax cable you have running between the head unit and the base unit?

You should be seeing far higher signal levels and I suspect that if one of the centre conductors or shields is open circuit then what you are seeing is picked up by the coax rather than the loop and head unit amplifier.

If you have a voltmeter to hand try measuring the voltage drop across the large 15 ohm resistor (marked 150 or 15R0) on the base unit. It should read some voltage across it if current is flowing through it. If it reads nearly 5V then the coax has a short circuit. If there is no voltage dropped across the resistor then the coax cable is open circuit.

Let me know what you find.

Regards,

Chris