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Testing VHF FM long distance

Hello,

a group of EA amateurs are planning a special activation.
The plan is to activate on VHF FM and try to reach a long distance S2S.
We are identifying summits well spaced between them so that we will try to cover a big distance in the range of 300 ~ 400 km.

We are trying to schedule the activation on a Sunday morning next July. I’ll post the confirmed date further on.

When activating in EA2 region we frequently reach distances up to 200 km with ease and we want to try further apart using verticals and yagis.

If you are interested to join this event and activate from a high summit we can agree and try for a S2S; just drop me an email to add you in the list (my mail correct at QRZ.com).

It would be great to try with CT, F and G activators.

Any comments welcome.

73 de Ignacio

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Hi Ignacio

Would you be able to use 2 m cw?

73 de Pedro, CT1DBS/CU3HF

It doesn’t need much enhancement to work IN53/IN63 from our contest group site in IO74 on 2m. But I don’t think I’ll be hearing too many EA1/EA2 summit stations from up here. But this sounds like it could be great fun and I look forward to seeing what you can achieve.

How much power are you planning to use?

Free space path loss over 300 km @ 145 MHz = 125.2dB (assumes LOS path of course)
If we assume 2 handheld radios with antenna gain -3dBi and output power 5 Watts
RX power = -94.21dBm which equates to 4.35uV RMS across 50 Ohms.

…assuming my calculations are correct.

Which is around S7 to S8.
I had a ~280 km contact in FM (5 Watt) from a summit with stable S7 so this sounds realistic.

FYI you could use the elevation profile feature in the sotamaps.org/range to check for the elevation profile including the earth curvature but it is currently restricted to max. 200 km. Maybe Andrew can increase that limit to let’s say 350 km to plan S2S contact. Why the limitation Andrew? @VK3ARR

73 de Joe

Guessing that it’s quite computationally intense.

It is a lookup to the satellite high profiles and currently can only be done when logged in to Sotamaps. Response time is super fast so I see no restriction in the server performance at the moment. The way how one can scale it, is the number of intermediate points between both coordinate pairs. I was involved with Rob when he set it up. The server that hosts it is the Iotamaps server that has enough space for the elevation data.
But let’s see what Andrew has to say about it.

1 Like

No longer true, it runs on the SMP server as Rob was pulling out of managing both SMP and iotamaps if I remember correctly. A typical query uses about 30% of RAM to load the SRTM tiles, so there’s a desire to keep the memory usage down given other things use the server (including SMP and it’s underlying Database).

Okay thanks for clarifying. Can I donate for more RAM :star_struck:
What would be the yearly cost?

About $60-120 USD for the next tier per year, depending on other parameters

I should add that we can make the tiles smaller which ironically will take up more space on disk but have lower memory usage when a query runs. But upping the limit to 350km would still require loading roughly as many tiles anyway

1 Like

What if you serialize the request in let’s say 100 km chunks?
And sorry for hijacking this thread. Maybe a moderator should split it. Thanks

Hi Ignatio,

I worked a s2s with John EI/VK6NU, activating EI/IE-054 (339m ASL) on 2m FM, from Shining Tor G/SP-004 (559m ASL,) last week, a distance of 331km.

John was using a hand held, 5 watts and small 2 element beam, I was using an X-50 colinear and FT-857.

GL Mike 2E0YYY

It’s basically doing that already - I can’t remember what size we split a standard SRTM tile down into, but it’d be in that ballpark. Each tile is about 77M on disk. The standard format is 16 bit signed integer, which gets loaded up into 64-bit integers because that’s the default size these days. So a tile will be about 300M in memory before page alignment which will make the actual size a bit bigger, although the resident set size (actual pages in memory) probably isn’t that large. If a point straddles a boundary or the interpreter’s garbage collection hasn’t quite run, then there’d be an overlap point where there’d be two tiles loaded, which I think is where the 30% figure is ultimately coming in (we have a 2G VM). I’m not spending time hacking the elevation service to force a GC run because I want that to be set and forget.

I’m not actually against upping the memory or the 200km, but we’d need to pay some more attention to what’s actually going on and the potential impact before just throwing money at the problem.

As far as I can see only one person has requested this feature. It is available elsewhere e.g. https://www.solwise.co.uk/wireless-elevationtool.html and
https://www.scadacore.com/tools/rf-path/rf-line-of-sight/ and
http://www.heywhatsthat.com/profiler.html

…and probably many other places.

Hello Pedro,
I’m afraid we will use FM voice, as most of the other activators don’t have CW skills.

Hello,
some activators will carry mobile rigs in the range of 30 ~ 50 watt, and some others will carry handhelds at 5w.
It all depends on what you have on disposal, including batteries.
Most of the activating places will be very high summits and not drive on ones, and therefore we will carry all the weight ourselves…

Thanks Richard, of course once the scheduled summits are identified we would analyze the profile path to see obstacles in between.

              x x x

One more question to the group, if we activate on FM, do you still recommend Vertical polarization or horizontal?

I am still willing to hear if any of the frequent activators closer to us (F) want to get involved and participate as well.

73 de Ignacio

Interesting experiment. In the late 70s I worked a ham sitting in a restaurant in Shreveport, Louisiana from Wellington, Colorado on 146.52 fm simplex. Distance about 1600km. He was using an HT; I had an Icom IC-22S at maybe 15w and 2 element quad @ 7m. Knew there was a hot tropospheric ducting opening going on since I was receiving Shreveport TV on channel 3 at P4. So, if you in the right place at the right time amazing things can happen! GL & 72
…Gil

SSB TOO PLEASE, am on Sw coast Uk and is possible to reach EA’s from here on 2m via me 8el 2m Quagi HB beam.

karl

One more question to the group, if we activate on FM, do you still recommend Vertical polarization or horizontal?

Horizontal gives some additional dBs of ground gain. However, for random QSOs vertically is recommended.

I am still willing to hear if any of the frequent activators closer to us (F) want to get involved and participate as well.

Can you choose a day with Es on 144 MHz? I’d listen for you guys, then. :wink:

Ahoi
Pom