Date: Fri, 2 Nov 2007 09:00:53 +0000
From: John Pumford-Green GM4SLV <gm4slv@sighthound.demon.co.uk>
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Subject: Re: LF: RE: 500 kHz report /  Great expectations
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On Thu, 1 Nov 2007 21:01:50 -0000
"Graham" <g8fzk@g8fzk.fsnet.co.uk> wrote:

> Good point's john .

Thanks Graham, 

This is an interesting discussion, but I think we're seeing things from
different perspectives, since you are used to groundwave and skip-zones
and such, whereas I'm in the strictly "DX sky wave" camp due to my
location!


>>My point was that Dave has said more than once that he struggles
>>to be heard, despite receiving other more distant stations with
>>seeming
>>ease.

>   But that's   the point, this band demonstrates the concept of 'skip 
> distance' quite elegantly, second only to  6 mtrs,  The transmission
> losses at this frequency seen to be quite low, but if your out of the
> skip distance , then even more power will not resolve the situation
> for semi local stations
> 

I was initially directing my "more power" point to stations like Dave
G3YMC who complain that they hear the "DX" stations like myself yet
fail to heard by those same stations. 

This isn't a question of extending the ground-wave signal further into
the "skip-zone" it's a question of radiating a similar level of power
than the remote station that you're already hearing and who is
obviously therefore in "skip range". 

The question of how much TX power is necessary needs to be addressed by
each station individually due to differences in antenna efficiencies.

To say "5W" or "10W" or "25W" is "enough to generate 100mW" is plain
wrong. 

The power needed is just that - "the power needed" - whether it be 5W
or 200W.


On the non-reciprocal nature of noise levels, I know all about the
effect of differing local noise floors! 

As an example I regularly (ie without fail) hear G3UNT in
broad daylight even in Summer, yet, due to the higher noise floor Brian
has, I have never been received myself by him in daylight.


> 
> The transmission losses at this frequency seen to be quite low,

I wouldn't know anything about this, as I've never been in the position
of hearing/working a good "local" groundwave range station. I'll leave
all discussion of the effects of increasing range, from the groundwave
region into the skip-zone and out the other side, to those lucky
enough to be able to try these things ;-)


All my contacts must be from some form of sky-wave path. I can hear/work
Mal G3KEV at any time of day. Even at >600km he's my nearest neighbour
but I'd guess (Alan can confirm this) that groundwave plays no part,
even in daytime.


> 
> For example, the s-meter on my R5003 , is calibrated in sinpo units ,
> 0 > 5 , connected to  my atu the receiver when in 'usb' (2.4 khz)
> reads a constant '3' on the meter uniform background noise. 

Conversely, my AR7030,  even with a  wideband 4kHz IF filter to feed the
grabber, shows no S-meter deflection in the daytime.

With a narrow 300Hz CW filter I can even use 30dB of extra RF
pre-amplification to good effect to pull out the likes of G3UNT from
the noise.

Brian runs (I think) quite modest power yet is audible 24/7 here. 

Have a listen to what he sounds like with 10Hz filter in at 
http://www.sighthound.demon.co.uk/gm4slv/g3kev_g3unt_clip_22_09_07.mp3

This was recorded at 10:25UTC on 22 Sept.


>>We shouldn't be afraid of the engineering needed to generate
>>highish powers, nor feel that it's against the spirit of QRP to
>>do so.<<<

> 25 watts looks to  be a reasonable feed to  a small system to  reach 
> something in the region of 100mW , 


I agree. That's what I use to get 100mW ERP. 

However, I don't think Dave runs even 25W though, and his antenna, by
his own admission, is very inefficient due to his sandy soil so he's
doubly handicapped:- 

Low TX power and poor efficiency. 

It's a simple equation.....

If your antenna is more inefficient than this example "small system" ,
perhaps due to poor ground/environmental losses then more than 25W is
needed. If it takes 100W or 200W then so be it.

One good thing about the OFCOM power limit being in terms of ERP and
not TX power is it should allow a level playing field, with everyone
being prepared to engineer their systems appropriately to meet the
limit, unless specifically interested in much lower ERPs for some
other reason.

I'd much rather (and I have) bite the bullet, build a bigger TX and try
to at least comfortably reach the 100mW ERP limit, after all 100mW is
tiny enough, but to purposefully restrict yourself further seems
pointless if your aim is aural, manual CW QSOs.



We need to make QSOs while we have access to the band. A log book full
of "called CQ, no reply" or "called GM4SLV, no reply" is of little
scientific value, or emotional value, as is a log book full of "worked
GxXXX again. RST599 as always, but then he's only 10 miles away"


We need to push the boat out now and put out as good a signal as
possible to get some work done on the band while we've got it. If it
takes a 200W TX then do it!
 

> 
>  May be we should regard this as a 'Digital band' in the true sense
> of the word ..
> 

No, we have an analogue band where signal strengths rise at the remote
location in direct relationship the the current flow in the antenna
producing them. The limiting factor is S/N ratio. Overcome the noise
and you'll be heard, assuming there's some propagation path. In Dave's
case I'd say that if can hear a station then there obviously is a path.


The answer, I'm afraid, is

"More Power Igor!"


-- 
John GM4SLV
IP90gg
Clousta, Shetland