83kms off the back of the beam.....

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G4WIM
Posts: 101
Joined: Thu Jan 29, 2015 8:36 pm
Location: Freckleton, Lancs

83kms off the back of the beam.....

Postby G4WIM » Thu Aug 31, 2017 9:59 am

Last night I was doing some 146.5MHz access tests into GB3FT and was beaming 315 degrees.

Surprisingly Tony G4CBW was getting my signal 83 kms to the South east off the back of the yagi.

Only running 5 watts to a 7 ele yagi !

https://www.dropbox.com/s/u554c9gmsee02 ... 7.jpg?dl=0

G4WIM
Posts: 101
Joined: Thu Jan 29, 2015 8:36 pm
Location: Freckleton, Lancs

Re: 83kms off the back of the beam.....

Postby G4WIM » Thu Aug 31, 2017 7:24 pm

Further tests with our beams pointing at each only 300mW required to establish communication

g0mjw
Posts: 280
Joined: Sat Sep 20, 2014 9:15 am

Re: 83kms off the back of the beam.....

Postby g0mjw » Thu Aug 31, 2017 8:54 pm

G4WIM wrote:Last night I was doing some 146.5MHz access tests into GB3FT and was beaming 315 degrees.

Surprisingly Tony G4CBW was getting my signal 83 kms to the South east off the back of the yagi.

Only running 5 watts to a 7 ele yagi !

https://www.dropbox.com/s/u554c9gmsee02 ... 7.jpg?dl=0


I am not sure that says a lot for the F/B of the yagi - but take care. A decent 7 element yagi will have about 13 dBi of gain, which is a factor of 20 so if you are feeding it with "only" 5W your EIRP is 100W.

The current EIRP limit for 146-147MHz is 50W. Even allowing for cable losses you are probably right up at if not over the maximum EIRP limit with just 5W power.

There are also some restrictions which are outlined in your NOV. For example there is a height limit of 20m AGL and it has an expiration date of 31 October 2017.

Mike

G4WIM
Posts: 101
Joined: Thu Jan 29, 2015 8:36 pm
Location: Freckleton, Lancs

Re: 83kms off the back of the beam.....

Postby G4WIM » Fri Sep 01, 2017 7:37 am

Hi Mike,
re restrictions on erp etc - yep all too well aware which is why I measured my cable & connector losses at 144, 432 and 1296MHz ( ECOflex 10 ) and found them to be slightly lower than claimed

The yagi has a claimed gain of 10.66dBd which when combined with feeder loss and patch lead to in line watt meter means a gain of 10dB so 5 watts is bang on the nose for 50 watts ERP.

measured loss cable loss antenna gain dbd antenna gain less feeder loss
144 12.5mtrs 0.49 10.66 10.17
432 13mtrs 0.9434 14.66 13.72
1296 15mtrs 2.0295 18.1 15.68

Also I thought ERP was based on antenna gain in dBd and not dBi which is why I converted the claimed gain from dBi to dBd, plus the NOW calls out ERP not EIRP.

As for yagi FB ratio - it's a wide band Powabeam with about 18dB F/B ratio so the numbers just about stack up to work Tony off the back

https://www.thedxshop.com/powabeam-ante ... cqm7f.html

As for antenna height, it's attached to my chimney so well under the required height plus I'm only about 4 mtrs ASL !

All said very pleased with making this contact over this non line of sight path.

edit - just checked my NOV and section 8f states,

(f) “effective radiated power” means the product of the power supplied to the antenna
and its gain relative to a half-wave dipole in a given direction

so dBd and ERP (not EIRP) it is, which means if you've been working on dBi and EIRP to calculate your ERP you could increase your tx power by 2dB or thereabouts ! :-)


73 Tim

g0mjw
Posts: 280
Joined: Sat Sep 20, 2014 9:15 am

Re: 83kms off the back of the beam.....

Postby g0mjw » Fri Sep 01, 2017 12:47 pm

Hi Tim,

ERP on its own is meaningless without a reference to what it is relative to. Its good to see it is defined but also strange to see its against the old fashioned dBd rather than dBi. Maybe it's easier to measure though these days it's normally calculated in software. The equations are for free space, but the antenna is not in free space, its over ground so it could get quite complicated. Maybe we can ask Murray to change it to 100W EIRP (or more!)

My antenna is also about 10 dBd gain with cable losses. I am not limited by the ERP but by my ability to generate power with acceptable shoulders to meet the strict don't radiate out of band requirement noted in the RSGB article. The out of band limits are not explicit in the NOV but good guidance is the ITU catagory A requirement which is relative to the power. The guidance is for spurious emissions to be at least 43 + 10 log P, or 70 dBc, whichever is less stringent. For 5W this is 50 dBc down, hence the aim to get -50dB shoulders and this is quite hard to achieve. I can just about get 3W from a 70W device with careful tweaking, but its marginal.

Its interesting where 2m will go, my best DX so far was 294km to G8LES from Winter Hill in a lift. Quite far from line of sight. You are a bit further north so there may be scope to extend that.

Mike

G4WIM
Posts: 101
Joined: Thu Jan 29, 2015 8:36 pm
Location: Freckleton, Lancs

Re: 83kms off the back of the beam.....

Postby G4WIM » Fri Sep 01, 2017 1:43 pm

Hi Mike,
yes quite a challenge to generate power which is clean - so I use 80 watt brick in class A followed by a 'brick wall' DCI-144 four resonator filter to attenuate the shoulders.

Side benefit is I can run talk back on 144.750MHz with no noticeable de-sense so must be pretty clean.

Having trouble measuring out of band spurious as it's so low and looks like broad band noise on the spectrum analyzers.

Plan is to go portable at some stage on 146, 437 and 1249 so trying to make everything as compact as possible, will have to post some pictures on progress.

73 Tim


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