[Xastir] DF object questions

[BDonnell at ar-northwest.com]

> -----Original Message-----
> From: xastir-bounces at xastir.org [mailto:xastir-bounces at xastir.org]On
> Behalf Of Jason Winningham
> Sent: Wednesday, October 13, 2004 8:40 AM
> To: Xastir Mailing List
> Subject: [Xastir] DF object questions
> 
> 
> I've got some questions about DF objects.
> 
> If I'm creating an object and select "DF Object" and "Omni Antenna" I 
> can select a heading, but this just shifts the center of an omni 
> circle.  I can also select signal strength and antenna gain.
> 
> Why isn't there any sort of signal strength or range indication if a 
> create a DF object with a beam antenna?
> 
> Is there a way to denote "negative" gain, i.e., I'm receiving 
> a signal 
> with strength S with X dB of attenuation?

S-meters on VHF rigs are not a terribly useful indication of signal
strength.  Most radios go from no indication (since most radios now have
LCD bar graphs, I mean no segments showing) for a signal level of say
0.25 uV, about where the squelch opens, and a full-scale indication
frequently occurs at levels as low as 10 uV.

They're not even all that accurate of HF rigs, but at least there's a
standard - 50 uV of RF equates to an S-9 signal, and every S-unit is
supposed to be 6 dB.  So theoretically, there should be 48 dB of signal
level difference between S1 and S9.  With the top of the scale being at
60 dB over S-9, that potentially give the HF radio's S-meter a bit over
100 dB of dynamic signal level display range.  Plus/minus the accuracy
of the metering system, of course!

In the case of the usual VHF/UHF FM rig, this zero to full-scale
indication might be taking place over a range of as little as 20-30 dB.
That might mean about 5 dB per bar on the bar graph (or however it's
represented) display.  This makes it a really sensitive indicator, if
you can achieve a signal level low enough for the S-meter to not be at
full scale.

If you're using xastir for DF-ing solo, you can create your own scaling
mechanism - choose settings of your attenuator to correspond to signal
strengths in the DF setup.  For shared information among an ad-hoc
group, you just have to hope everyone is using reasonable sense in how
they determine signal strength, or you have to work to coordinate and
systematize your postings, in a way that makes sense.

> 
> And on a related (but off topic) note, does anyone know the 
> beam width 
> for the Arrow dual band handheld yagi?
> 
> I'm not sure if these are protocol questions or xastir questions, but 
> I'll start here since xastir is my software of choice.
> 
> -Jason
> kg4wsv
> 

73, Bob, KD7NM