[OZAPRS] On possibilities with short HF whips

Fri Dec 8 10:56:37 AEDT 2017

Will be using 4G where possible

Sent from my iPhone

> On 8 Dec 2017, at 9:19 am, Glen English VK1XX <glenlist at pacificmedia.com.au> wrote:
> 
> 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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