[OZAPRS] On possibilities with short HF whips
Mathew McKernan
mathew at mmckernan.id.au
Fri Dec 8 17:39:45 AEDT 2017
I did similar with a Codan autotune on my Landcruiser, mounted above the spare wheel carrier connected to my Codan 9323.
Hit the line at the same spot... was waiting for smoke to fill the cabin. I was pleased it didn't, but disappointed as it would have been pretty impressive!
________________________________
From: OZAPRS <ozaprs-bounces at aprs.net.au> on behalf of Glen English VK1XX <glenlist at pacificmedia.com.au>
Sent: Friday, 8 December 2017 5:26:29 PM
To: ozaprs at aprs.net.au
Subject: Re: [OZAPRS] On possibilities with short HF whips
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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