[OZAPRS] On possibilities with short HF whips

Fri Dec 8 10:19:50 AEDT 2017

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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