[OZAPRS] Higher beacon rate HF versus VHF?

David and Justine Olsen davejust at bigpond.net.au
Tue Mar 31 11:31:07 EST 2009


Geoff

I am happy to provide 40m Gate 24/7 from my location. I recognise I  
have a bit to learn but happy to take advice.

David

On 31 Mar 2009, at 08:47, Geoff wrote:

> 10 minutes for normal stations, however the PRIMARY NET STATION should
> beacon more often, to give everyone else a reference to tune to.
> I think we had defined the primary and secondary net stations to  
> beacon
> every 5 minutes.
>
> On 30m we already have these established (Richard/Ray please  
> correct me if
> I'm wrong)
> Primary = VK3MY-4
> Secondary = VK4DMI-4
>
> On 40m and now 20m we need to work out who will be running a 24x7  
> HF Gate on
> these bands and allocate NET roles accordingly....
>
> Regards,
> Geoff
>
>> -----Original Message-----
>> From: ozaprs-bounces at aprs.net.au [mailto:ozaprs- 
>> bounces at aprs.net.au] On
>> Behalf Of Richard Hoskin
>> Sent: Monday, 30 March 2009 8:01 PM
>> To: 'Australian APRS Users'
>> Subject: RE: [OZAPRS] Higher beacon rate HF versus VHF?
>>
>>
>>
>> Hi All,
>>
>> Remember on HF you are sharing this band with all other APRS users  
>> world
>> wide and even though you can not hear them they may hear you. (You  
>> just
>> have
>> to look at some of the posts on this list from HF APRS operators  
>> in other
>> countries for evidence of this). Also 300 baud is 1/4 the speed of  
>> VHF
>> APRS
>> which means you can only fit 25% of the stations on the channel if  
>> you use
>> the same beacon rate.
>>
>> Lets see, HF APRS increases the coverage area from roughly 200,000  
>> Sq Km
>> using 3 hops to potentially 75 Million SQ KM. An increase in  
>> coverage area
>> of 375 times. At 300 baud you get a reduction in band capacity of  
>> 4 times.
>>
>> Leaving your beacon rate the same as for VHF or increasing it some  
>> what
>> really doesn't make a hole lot of sense.
>>
>>
>> That's why the world wide recommended minimum APRS beacon rate for  
>> HF is
>> 10
>> minutes or more.
>>
>> Or another way to look at it; an average length APRS Posit packet  
>> takes 3
>> to
>> 4 seconds to transmit on HF. Assuming a channel efficiency of 30%  
>> for ax25
>> this results in a maximum of 7 stations being able to transmit per  
>> minute.
>> At a transmission rate of one posit per 10 minutes the maximum  
>> number of
>> stations that can be in a single APRS Gate's coverage area is 70  
>> stations.
>> This will be less as the Net stations transmit frequently and  
>> messages
>> and/or tuning may be under way on the channel. HF Propagation is  
>> also an
>> important factor.
>>
>> Cheers
>> Richard
>> VK3JFK
>>
>>> -----Original Message-----
>>> From: ozaprs-bounces at aprs.net.au [mailto:ozaprs- 
>>> bounces at aprs.net.au] On
>>> Behalf Of Jack Chomley
>>> Sent: Monday, 30 March 2009 6:45 AM
>>> To: Australian APRS Users
>>> Subject: Re: [OZAPRS] Higher beacon rate HF versus VHF?
>>>
>>> At 11:00 PM 3/29/2009, you wrote:
>>>> Jacks success at being received by my HF iGate with 600mW,  
>>>> complaints
>>>> about QRM etc got me thinking about beacon rates for HF vs VHF.
>>>>
>>>> Given the low number of HF stations, the vastness of Australia, the
>>>> vagaries of HF and the fact that HF stations do not digipeat to HF,
>>>> and perhaps if I go on, shouldn't digipeat to VHF, I believe beacon
>>>> rates on HF should be higher than on VHF. What do others think?
>>>>
>>>> David
>>>> VK4MDX
>>>
>>> David,
>>> I have been using a beacon rate of 2 minutes on my motorcycle system
>>> running 6 watts on 30m with an Icom 703, SCS DSP TNC, Garmin
>>> 16-HVS  GPS.  The performance has been good over the last 12 months,
>>> many of the beacons were missed, but I put that down to the low  
>>> power
>>> and antenna waving around while mobile.
>>> Back in January, I changed the transmit format of the APRS data
>>> frames to the compressed format and my "hit" rate immediately went
>>> up. Probably because of the shorter packets, meant less chance of
>>> them being corrupted.
>>> See my Jan 15th '09 track log....
>>> http://aprs.fi/? 
>>> call=VK4JRC-15&dt=1231977600&mt=m&z=11&timerange=3600
>>> Since the hit rate has gone up, I can now lower the beacon rate and
>>> still get a good track record.
>>> Bike here:
>>> http://www.radiotelemetry.net/html/hf_mobile_aprs.html
>>> Personally, I think that IF there are enough IGATES, there is
>>> probably no reason to have a high beacon rate, nor need to run
>>> anymore than about 20 watts, but the secret of success is to use
>>> compressed format APRS data.
>>> Yesterdays test also proved that when there was QRM on the  
>>> frequency,
>>> I managed to get some hits in between the contest stations, that  
>>> were
>>> just off the 40m frequency. Shorter frames, less chance of  
>>> corruption ;-
>> )
>>> My antenna for yesterday's test was a Buddipole vertical, setup  
>>> on an
>>> 8ft tripod, in the back yard, the counterpoise was 1 electric fence
>>> wire above ground radial, deployed towards the South. The vertical
>>> element a Versa-T,  1 arm section, coil, with 5 section shock-corded
>>> military whip, on top of the coil.
>>> See Buddipole:
>>> http://www.buddipole.com/
>>>
>>> 73  Jack VK4JRC
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Ozaprs mailing list
>>> Ozaprs at aprs.net.au
>>> http://aprs.net.au/mailman/listinfo/ozaprs
>>
>> _______________________________________________
>> Ozaprs mailing list
>> Ozaprs at aprs.net.au
>> http://aprs.net.au/mailman/listinfo/ozaprs
>
> _______________________________________________
> Ozaprs mailing list
> Ozaprs at aprs.net.au
> http://aprs.net.au/mailman/listinfo/ozaprs

_______________________________________________
Ozaprs mailing list
Ozaprs at aprs.net.au
http://aprs.net.au/mailman/listinfo/ozaprs



More information about the Ozaprs mailing list