Re: HF LOOP


Paul Newland
 

Hi Martin
I am grateful for your interest and truly respect what you have had to say. I would like to address the comments that you have kindly offered and so will offer a little clarification, that I believe is best made by addressing your individual observations, that I hope you will not object to me quoting below, in parenthesis.

(Looking at your screen grab and based on the waterfalls, I'd say that the middle is providing the best Signal to Noise ratio of about 20dB, the top is the next best with a S/N of about 10dB and the bottom has a S/N of about 8dB).

The top one is my Wellbrook ALA1530LN on the HiZ Port of a SDRPlay RSPduo (Master), the middle one is the Slave receiver fed by the CCW loop-amplifier and the bottom one is a 20M longwire (with tuner). 

The loops are only about 2M apart (not from choice), currently in a N/S orientation and are both centered about 1.5M above ground level.

(However you are not really comparing like with like, as all the receivers have different gain settings and two of them have also got decimation enabled).

The settings for all three rx's  were configured each for their individual optimum performance in the prevailing conditions and confirms my opinion that the CCW was the best performer at the time. I would however, like to emphasise that generally the performances of this and the Wellbrook are pretty close and under other conditions the results may well have been different with the Wellbrook often providing the better SNR, albeit with less gain (but not always) and over their common frequency ranges I prefer to use the CCW (but it's good to have a choice).
In this mode decimation wasn't available (?) for the RSP2 , which is the third/lower one.

Unsurprisingly perhaps the tuned longwire  provides more gain within it's range, but is always noisier.

(Comparing antennas is quite difficult, as variations in propagation, angle of arrival and antenna pattern all complicate the issue).

I do not have the knowledge, by a very long shot, the experience, or equipment to conduct a proper test and would really appreciate it if someone were to do one.

This was the best that I was able to achieve at that time and in the prevailing conditions, within the limits of my ability and setup - the ultimate caveat.

 I have a lot to learn with regard to SWL (I have been forced to learn morse code) and at 81, probably not that long to do so, when time is shared with diving and domestic trifles; although come to think of it, having been naughty enough to survive this long I may well have plenty of time on my hands whilst effectively being confined to property for an indefinite time....

Anyway, thank you again for taking the time to comment.

Best Wishes
Paul





On Tue, 17 Mar 2020 at 10:05, Martin - G8JNJ via Groups.Io <martin_ehrenfried=yahoo.com@groups.io> wrote:
On Tue, Mar 17, 2020 at 08:30 AM, Paul Newland wrote:
I should have clarified that: top to bottom are Wellbrook (SDRplay RSPduo -M), CCW, (Rspduo - s) and longwire (RSP2)
Hi Paul,

Are you sure about this ?

When receiving signal you are always trying to maximise the wanted signal, and minimise unwanted ones (including noise). Lots of folks concentrate on the overall signal strength, but it's the Signal to Noise ratio that matters.

Looking at your screen grab and based on the waterfalls, I'd say that the middle is providing the best Signal to Noise ratio of about 20dB, the top is the next best with a S/N of about 10dB and the bottom has a S/N of about 8dB.

However you are not really comparing like with like, as all the receivers have different gain settings and two of them have also got decimation enabled.

Comparing antennas is quite difficult, as variations in propagation, angle of arrival and antenna pattern all complicate the issue.

As Chris has already mentioned the MLA-30, has a few failings, one of which is limited common mode suppression, which means that the coax cable is often picking up more signal than the actual loop part. It also has a fairly poor frequency response and IMD performance, and can easily be overloaded, especially if the gain is increased too much, producing lots of spurious signals that my not be present when using other antennas.

Some notes on the MLA-30 and other active antennas can be found on this webpage.

https://www.g8jnj.net/activeantennas.htm

Regards,

Martin












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