[OZAPRS] Grounding of HF Antenna for APRS

[Glen English VK1XX]

BTW everyone, if this is too off topic I can carry this privately. I 
have experience with MF/LF antennas.....

HF30FX ahh yeah , right previous generation base loaded compared to the 
centre loaded ones

yes, very much ground dependent. anything under 2:1 is probably OK, with 
various ground arrangements see if there is a pronounced dip anywhere

the sharper the dip, the more likely the efficiency is good .

My approach would be to ginore the VSWR once below 2:1 and try and get 
the sharpest looking VSWR versus frequency curve

think of it this way :

If it was a dummy load, it would be good at all frequencies

if it was a high Q tuned circuit, then it would be good VSWR at only one 
freq and infinite everywhere else

Your antenna will be somewhere in between a dummy load and a pure tuned 
circuit...probably about 2:1 SWR BW of 50kHz (assume centre matched to 
1:1)  indicates reasonable efficiency.




On 4/12/2017 12:13 PM, vk4tec at tech-software.net wrote:
> Diamond HF30FX
>
>
>
> -----Original Message-----
> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen English VK1XX
> Sent: Monday, 4 December 2017 11:09 AM
> To: ozaprs at aprs.net.au
> Subject: Re: [OZAPRS] Grounding of HF Antenna for APRS
>
> well, there are alot of assumptions for pre cut antennas on vehicles for HF.
>
> So I wouldnt pay too much attention to SWR once it is below 2:1. What sort is it ? WHat model / URL ?
>
>
> On 4/12/2017 11:58 AM, vk4tec at tech-software.net wrote:
>> I went to see an engineer mate
>>
>> He gave me some brass plate
>>
>> I am cutting out a plate that will have a braid strap coming off it
>>
>> That should do the trick - he said the VSWR should come down even further
>>
>> Nudge bars are $1000
>>
>> Andrew
>>
>> -----Original Message-----
>> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen English VK1XX
>> Sent: Monday, 4 December 2017 7:35 AM
>> To: ozaprs at aprs.net.au
>> Subject: Re: [OZAPRS] Need a hand
>>
>> yeah that will work. it would be out of the weather, and get covered with oil/grease and probably weather seal it.
>>
>> being close to the feedpoint actually isnt that necessary, maybe no more than 1/20 of a wavelength, though , that is probably a good number. so max strap length 1.5m for that freq.
>>
>>
>> On 4/12/2017 8:27 AM, vk4tec at tech-software.net wrote:
>>> Glen
>>>
>>> I am thinking that maybe just a strap that fits in the gap between the bonnet and the side wall.
>>>
>>> I can sink a screw into the bonnet just inside
>>>
>>> That way it would be as close to the feed point as possible
>>>
>>> I would drill into the top side of the bonnet but that equals a
>>> divorce LOL
>>>
>>> -----Original Message-----
>>> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen
>>> English VK1XX
>>> Sent: Monday, 4 December 2017 7:23 AM
>>> To: ozaprs at aprs.net.au
>>> Subject: Re: [OZAPRS] Need a hand
>>>
>>> In looking for a place to attach a ground strap, consider that ideally, you want the largest continous area of metal. That is probably the engine bay firewall (which would attach to the upper body, roof etc) , fender mounts,  or in the rear, hinge mounts of the rear hatch, etc.
>>>
>>> Anyone else have any input here  on where to connect on a modern vehicle to maximise surface area ?
>>>
>>> comeon. ???
>>>
>>> I am a bit out of tough on modern vehicles. (I have a 2005 XC90 which
>>> if you pass a RG58 through a door seal will squash it flat and cause a
>>> short... hence requiring coax entry through a bung in the spare tyre
>>> well under the vehicle)
>>>
>>>
>>>
>>>
>>>
>>>
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