[OZAPRS] On possibilities with short HF whips
Matthew Cook
vk5zm at bistre.net
Fri Dec 8 18:16:05 AEDT 2017
Victoria is complicated, so complicated in fact they have a book you
download...
https://www.vicroads.vic.gov.au/~/media/files/documents/business-and-industry/heavyvehiclesheightclearanceonroadsnov2009.ashx?la=en
73
Matthew
VK5ZM
On 8 December 2017 at 16:56, Glen English VK1XX <
glenlist at pacificmedia.com.au> wrote:
> 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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