[OZAPRS] On possibilities with short HF whips
vk4tec at tech-software.net
vk4tec at tech-software.net
Fri Dec 8 20:33:08 AEDT 2017
What a bright spark
-----Original Message-----
From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen English VK1XX
Sent: Friday, 8 December 2017 6:18 PM
To: ozaprs at aprs.net.au
Subject: Re: [OZAPRS] On possibilities with short HF whips
Ian was it 1500V overhead, or the now days 25kVAC ?
On 8/12/2017 6:32 PM, Ian Bennett wrote:
> I remember back in the 80's when I was in uniform and in Brisbane, a
> radio vehicle drove over the railway line near Enoggera with the HF
> whip still up. Made a BIG flash (apparently), blew a tyre, shutdown
> the train network for an hour or so and welded the 106 to it's mount.
> I have two HF whips mounted on the bullbar of my 100 Series; my home
> made APRS antenna is just shy of 2m long (that was the length of the
> donor antenna that I dismantled) and is 3150(ish) mm floor to tip. I
> haven't had any dramas like the one mentioned above however I tie them
> back when negotiating "tight" spaces.
> Will be a different story when we get our truck based motorhome but I
> have a cunning plan for that ;-)
>
> Ian
>
> On 08/12/17 17:39, Mathew McKernan wrote:
>> 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-acce
>>> ss/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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>>
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