Re: LF: about guns, water pistols and dripping tabs

[Andy Talbot <andy.g4jnt@googlemail.com>]

Re ERPs.   I think mine is mostly right-ish.   The antenna is a 7m high Tee with a large top-hat, so its effective height is pretty much the same.   At a wavelength of 600m, that gives a radiation resistance of around 0.2 ohms.   Load resistance of the whole antenna system is close to 50 ohms (very convenient that !!) and with 100 Watts pumped into it means ERP could be 0.4 Watts or 26dBm.   But there's a lot of wet trees and bushes around the antenna now, and Its quite reasonable to expect half the signal to be lost in them.

 

When the weather improves, I'll go off and have a go at measuring accurate field strengths, but have  gut-feeling I'm wihin 3dB of the estimate.

Andy
www.g4jnt.com

2010/1/21 Roger Lapthorn <rogerlapthorn@gmail.com>

Hi Rik,

This is most interesting. I notice that M0BMU was running with 50mW ERP last night, so it might be worth plugging in his reports as well for last night. My ERP was based on (a) field strength measurements done some time ago by M0BMU and (b) calculations based on my estimate of effective height and antenna current. I estimated it as being in the region of 500uW to 2mW but Jim seemed to believe the 1mW ERP was a fair estimate with quite large error margins. It would be interesting to know if M0BMU still believes the 1mW ERP is a correct figure. I have not made any further improvements since Jim's last estimates some 6-8 weeks ago.

What is the path length difference between us all over to you? That will also have some effect on the relative levels.

BTW, Dom Baines M1KTA quoted something interesting to me today: "Terman's Radio Engineering Handbook (1948)
stated the maximum working distance for 1 kW 500kHz over salt water was 1,500 miles!". So, I need to up my power then!

73s
Roger G3XBM

2010/1/21 Rik Strobbe <rik.strobbe@fys.kuleuven.be>

Eddie, Andy, Roger, all,

the nice thing about WSPR and the www.wspr.org web site is that a lot af data is available.
I copied the my spots (past 7 days) of G4JNT, G3XBM and G3ZJO from the web site and threw them in the mill to check how often I copied  at least 2 of the 3 calls in the same time slot:
I took only the night time spots as I assume that propagation then is 1 hop ionospheric and small differences in distance are less important.

* G3XBM - G3ZJO: 6 'hits', average difference = 8dB (in favor of Roger)
6 data sets is a bit low to to proper statistics, but the difference of 8dB between Roger and Eddie fits well into the claimed ERP's (1mW and 200uW = 7dB)

* G4JNT - G3XBM : 60 'hits', average difference = 15dB (in favor of Andy)
15dB difference would mean that if Roger's 1mW ERP is correct that Andy would run "only" 30mW ERP ?
But the standard dev. is 6dB, so it could be (a more realistic) 120mW as well ...

* G4JNT - G3ZJO: 6 'hits', average difference = 23dB (in favor of Andy)
Nice, this is the sum of the previous values (as iit should be ;-) )

All values are give or take some dB, but they seem to make sense.

73, Rik  ON7YD - OR7T

At 23:14 20/01/2010, you wrote:

Yeh ! Congratulations Roger.
 
Lubos you have the Water Pistol, can you now RX a tiny Dripping Tap, my QRPp 200uW ERP is on..
 
73
 
Eddie G3ZJO
 
-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [ mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Andy Talbot
Sent: 20 January 2010 22:01
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: G3XBM
 
Congratulations,  "water pistol"
1200km - a very comfortable margin too.
 

Andy
www.g4jnt.com

2010/1/20 Lubos OK2BVG <bvgbob@hotmail.com>
Hello Roger, LF!
This moment is just now:

2136  -7  0.2   0.503874  0 G4JNT IO90 23

2142 -29 -0.5   0.503910  1 G3XBM JO02 0

Congratulation!

Lubos, OK2BVG, JN88KS

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