Re: LF: Topband Test

["Chris" <c.ashby435@btinternet.com>]

Thanks again Andy and Markus,

Yes, my feeling is that the reflective wave shift is due to doppler as the layer changes height. We need to try it again over a longer period. It is true there are a lot of aircraft between us, but would the result have been so smooth?

Has this effect been seen on 137kHz? The info I have seen on near vertical incidence/reflection suggest it should.

Any thoughts on this appreciated, thanks for taking the time to comment.

Chris, G4AYT.

----- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Thursday, March 03, 2011 8:40 PM

Subject: Re: LF: Topband Test

No, it definitely is due to ionospheric shift.   30m/s is no big deal over the period of the day/night transition.  30 minutes at that speed would be a mean change in height of 54km.   Not  unrealistic for an E layer (??) height of 120km

 

Try to find a copy of G3PLX's article

 

'JNT

 

On 3 March 2011 20:19, Markus Vester <markusvester@aol.com> wrote:

Hi Chris, thanks for sharing this unusual observation.

 

From your screenshot, the split was up to about 0.35 Hz, or 0.2 ppm of 1.8 MHz. Interpreted as Doppler, a reflector would have to move at least 30m/s radially from your baseline. This seems a bit fast for an ionospheric day-to-night shift.

 

Another possible explanation could be airplane scatter. Large airliners are known to have a large radar cross section at HF. Seeing that on 160 m may seem extreme, but considering the wingspan of an A-380 (80 m), half-wave resonant scattering is a very real possibility. The downward slope of the Doppler shifted frequency would also be indicative of an object passing by at constant linear velocity.

 

Best 73,

Markus (DF6NM)

From: Chris

Sent: Thursday, March 03, 2011 7:55 PM

To: RSGB LF Group

Subject: LF: Topband Test

Hi All,

Yesterday evening Pete, M0FMT, transmitted QRSS on topband for a test. An unexpected effect was noticed with the trace splitting in two. Nothing new or 'earth shattering' I expect, but new to us and worthy of further experimentation.

See the result and conclusion on my website http://qsl.net/g4ayt on the bottom of page 1.

I have never seen this effect on 137, even with quite strong audible signals, maybe others have.

Vy 73,

Chris, G4AYT, Whitstable, UK.