[600MRG] 630m ground-wave testing - we need more than anecdotal comments

[John Langridge]

I found a data entry error while working with my spreadsheet.  Instead of no more than 1 mW ERP in the original test, its actually no more than 10 mW ERP.

After making the adjustment today, I am revising the 6-9db increase to 50 mW ERP from this antenna.  That feels more realistic and I think you will agree after you hear what the antenna is.

Sorry for the confusion.. I knew something didn't look right and checking the numbers confirmed that..

73!

John XIQ




________________________________
 From: "Ralph Wallio, W0RPK" <W0RPK at netins.net>
To: 600mrg at w7ekb.com 
Sent: Sunday, January 12, 2014 8:11 AM
Subject: Re: [600MRG] 630m ground-wave testing - we need more than anecdotal comments
 

Thanks Steve ---

We appreciate your suggestion of the possibility of using FCC AM broadcasting ground-wave field-strength graphs as a tool toward developing reasonable expectations for performance of regional 630m ground-wave digital networking.  Our understanding of the importance of ground-conductivity to ground-wave propagation at 630m is important.

Radio-TimeTraveller Bill Scott, WE7W, explains and expands on these graphs during a very helpful series of discussions of medium-wave AM broadcasting ground-conductivity issues:

http://radio-timetraveller.blogspot.com/2011/06/field-strength-calculations-ground.html
http://radio-timetraveller.blogspot.com/2011/06/field-strength-calculations.html
http://radio-timetraveller.blogspot.com/2011/06/field-strength-measurements-calculating.html

Paul Lawson, VK5SL, also helps us with his discussion and spreadsheet available via http://500kc.com/VK5SL/index.htm.

What follows is my attempt to understand how this spreadsheet could be applied to use of our Ham Radio digital modes on 630m over ground-wave propagation distances.  Perhaps we can use past and future ground-wave test results to further understand what calculations in this spreadsheet mean to us.

This table includes transmit and receive testing stations, their path lengths and ground-conductance as given by an FCC map (see the top link above for this map).  In the ground-wave path loss calculator we can use 0.475MHz, 100W transmitter output, losses set to 0dB and antenna gain of -20dBi for WD2XSH/29 and WD2XSH/34 (for 1Weirp) and antenna gain of -7dBi for WD2XSH/7 (for 20Weirp).

We can then use path distances and ground-conductances in the spreadsheet to calculate mV/m signal strengths and add them to the table.  Remarks are added so we understand every test in the table produced, or might have produced, acceptable performance.  (Table entries are ordered by calculated signal strength.)

WD2XSH/7  (W5JGV LA) ->  K5BTP (LA)            250km   8mS/m 0.0144mV/m  Numerous tests proved low error-rate MSK31
WD2XSH/29 (KN8AZN OH) -> WB8ILI (MI)           200km   8mS/m    0.0058mV/m Numerous tests proved very low error-rate BPSK10/31
WD2XSH/7  (W5JGV LA) ->  AA5AM (TX)            350km   8mS/m 0.0050mV/m  Numerous tests proved very low error-rate MSK31
WD2XSH/34 (W0RPK IA) ->  KC0TKS (MO)           300km  15mS/m  0.0044mV/m  Numerous tests proved very low error-rate BPSK10/31
WD2XSH/34 (W0RPK IA) ->  WD2XSH/16 (WE0H MN)   440km  15mS/m  0.0014mV/m  One test hinted at a low-error-rate BPSK31
WD2XSH/34 (W0RPK IA) ->  WD2XSH/19 (K9EUI IL)  440km 11.5mS/m 0.0009mV/m A few tests hinted at a low-error-rate BPSK31

This table estimates receive signal strength but it does not describe receive station configurations, local noise, etc.  We understand that receive antenna, receiver performance and local RFI can seriously impact digital reception error-rate.

It is important to gather much more 630m ground-wave propagation WSPR SNR and digital error-rate data to more completely understand path distance and ground-conductivity issues.  Toward his end, we will soon apply WSPR to another path:

WD2XSH/31 (WA1ZMS VA) -> W0RPK (NC)            265km   2mS/m 0.0003mV/m

This predicted field strength is only a third of the bottom entry in the above table.  If WSPR results are worse than -11dBsnr, BPSK31 would not yield acceptable error-rate results.  If it is worse the -17dBsnr, ditto for BPSK10.

TNX es 73 de Ralph Wallio, W0RPK
http://showcase.netins.net/web/wallio/







On 1/6/2014 12:57 PM, sbjohnston at aol.com wrote:
>   I would think that the basic groundwave propagation of LF and MF would have been well-documented in the past.  That's why I mentioned GWEN and maritime experience.  Add to that the data for the low-end of the broadcast band, and one should know what to expect.
> 
> http://www.fcc.gov/encyclopedia/am-broadcast-groundwave-field-strength-graphs-sections-73183-and-73184
> 
> The issue for amateurs is the limited antennas and low transmitter power, especially for emergency portable setups.  Perhaps the reports gathered for the present experimental stations can provide some data.
> 
> Steve WD8DAS
> 
> sbjohnston at aol.com
> http://www.wd8das.net/
> --------------------------------------------------------------------
> Radio is your best entertainment value.
> --------------------------------------------------------------------
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