[OZAPRS] On possibilities with short HF whips

Fri Dec 8 15:07:17 AEDT 2017

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> 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
> 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 wrote:
>>
>>> You are not telling me anything new
>>>
>>> -----Original Message-----
>>> From: OZAPRS [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
>>> 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 wrote:
>>>
>>>> Go for a walk
>>>>
>>>> -----Original Message-----
>>>> From: OZAPRS [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
>>>> 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 wrote:
>>>>
>>>>> Blind ?
>>>>>
>>>>> Tracker has CD
>>>>>
>>>>> -----Original Message-----
>>>>> From: OZAPRS [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
>>>>> 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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