[OZAPRS] On possibilities with short HF whips
Glen English VK1XX
glenlist at pacificmedia.com.au
Fri Dec 8 17:26:29 AEDT 2017
what are the recommendations and user practical limits for Melbourne ?
(trams)
Canberra here you'll get into trouble ~ 4m
I had the loop on my vehicle when I was driving in Melbourne a fair bit....
I once hit a tram line with my car roof antenna heatshrink insulated
helical at Racecourse Road, Kensington... it made a huge pop in the
receiver but otherwise no damage...
On 8/12/2017 3:07 PM, Matthew Cook wrote:
> This is also worth considering when looking at larger HF whips.
>
> http://www.rms.nsw.gov.au/business-industry/heavy-vehicles/road-access/restricted-access-vehicles/4-6m-high.html
>
> Each state has their own variations to the above, nationally
> un-restricted is 4.3m.
>
> 73
>
> Matthew
> VK5ZM
>
> On 8 December 2017 at 14:03, Graeme <graeme at abrona.com.au
> <mailto:graeme at abrona.com.au>> wrote:
>
> Thanks Glen.
>
> Obviously my decision against buying a 2.2m centre loaded 40m whip
> because it would bend in the wind to its disadvantage in favour of
> a base loaded 1.4m whip wasn't a good one for multiple reasons.
>
> Graeme 2HFG
>
> -----Original Message----- From: Glen English VK1XX
> Sent: Friday, December 8, 2017 10:19 AM
> To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
> Subject: Re: [OZAPRS] On possibilities with short HF whips
>
>
> Ran some NR predictions for 10 MHz for Brisbane Sydney, and 7 and 3.5
>
> and also some more details calcs on the Diamond 1.4m logn base
> loaded whip
>
> turns out to be ~ 3% efficiency.
>
> for the -15dBi TX terminal (1.4m base loaded whip with suboptimal
> loading Q)
>
> yep, in daytime, single hop 750-1200km , 100W into the antenna,
> expect
> around 15dB SNR for the 300 baud modem given a good receiver
> antenna and
> setup...with a modem like DireWolf that can cope with frequency
> variations. Be sure you know your radio frequency offset before
> you start.
>
> with same length whip on 7 MHz, expect about 300-700km in
> daylight, but
> not much use outside that time and distance.
>
> All of this means is for 300 baud FSK packet mode and 100W, the
> mode is
> unsuitable for low efficiency mobile antennas like base loaded short
> whips. (3% or less efficiency at 10 MHz, 2% at 7 MHz etc)
>
> All this points to: (in my opinion) needing a >=2.2m long whip
> instead
> of a 1.4m long whip.
> and an antenna with a non base loaded structure (for 300 baud packet)
>
> Get your antenna efficiency up to 10% at 7 MHz and then now you
> have an
> idea setup 24 hours, single freq .... 10 MHz almost good enough except
> for the wee hours 2am-sunrise when you will be asleep anyway.
>
> So the lesson here, 300 baud packet needs decent antenna efficiencies
> mobile.
> hence the need for a mode that does about 6dB better
>
> sure we can do alot better than 6dB, but 6dB better mode is what is
> required to work on the 1.4m base loaded whips.
>
> Otherwise for 300 baud FSk packet, it needs to be teamed up with
> antenna
> efficiency >= 8%, implying something with a feedpoint of around 2
> ohms
> Rr and not too lossy loading and matching... a whip of 2 meters
> tall at
> 10 MHz with continuous or 1/3 loaded structure. Base loaded structures
> are the worst !
>
> The longer 1.8m long CB helical whips are a bit hard to find these
> days.
>
>
>
>
>
>
>
>
> g
>
>
> On 7/12/2017 6:36 PM, Glen English VK1XX wrote:
>
> ok
>
>
> On 7/12/2017 6:24 PM, vk4tec at tech-software.net
> <mailto:vk4tec at tech-software.net> wrote:
>
> You are not telling me anything new
>
> -----Original Message-----
> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au
> <mailto:ozaprs-bounces at aprs.net.au>] On Behalf Of Glen
> English VK1XX
> Sent: Thursday, 7 December 2017 5:10 PM
> To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
> Subject: Re: [OZAPRS] Hf gates CD
>
> base station 700-1500km away will hear you, but you wont
> hear a station 50km away.
>
>
> On 7/12/2017 5:57 PM, vk4tec at tech-software.net
> <mailto:vk4tec at tech-software.net> wrote:
>
> Go for a walk
>
> -----Original Message-----
> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au
> <mailto:ozaprs-bounces at aprs.net.au>] On Behalf Of Glen
> English VK1XX
> Sent: Thursday, 7 December 2017 4:55 PM
> To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
> Subject: Re: [OZAPRS] Hf gates CD
>
> tracker might well have CD but:
>
> 1) Consider that in the mobile, you wont hear any
> stations less than the skip distance (unless they are
> 10km away) . The daytime skip distance might be
> 700km.... so anyone inside that distance you wont
> hear cause the ionosphere wont support it..it wont
> support any angles higher than perhaps 45 degrees.
>
> The base station though will hear lots of
> transmissions from lots of stations >700km to 1500km
> away, so there would be significant collision chance
> if the position update is too often. Maybe 10 minutes
> might be suitable. I dunno why people run..
>
> 2) With a 5% to 10% efficiency mobile you wont hear
> too much unless the propagation is optimal...
>
>
> glen
>
>
>
>
>
> On 7/12/2017 5:41 PM, vk4tec at tech-software.net
> <mailto:vk4tec at tech-software.net> wrote:
>
> Blind ?
>
> Tracker has CD
>
> -----Original Message-----
> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au
> <mailto:ozaprs-bounces at aprs.net.au>] On Behalf Of
> Glen English VK1XX
> Sent: Thursday, 7 December 2017 2:46 PM
> To: ozaprs at aprs.net.au <mailto:ozaprs at aprs.net.au>
> Subject: Re: [OZAPRS] Hf gates
>
> but how does this matter?
>
> You will be transmitting on a frequency blind
>
> there will be receivers you cannot control
>
> There will be any number of propagation modes you
> cannot control...
>
>
>
> On 7/12/2017 3:34 PM, Andrew Rich wrote:
>
> Hi
>
> Can I get a list of hf gates on 10.147
>
> In my planning for the Xmas run
>
> Cheers
>
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