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VHF range problem


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Hi All

My boat still has the original VHF fitted (now 16 years old) and seems to be having some problems with range. Over the weekend, calling Mutford and Lowestoft from short distances seemed to be okay, as did the river bridges. However, and further than about 0.5 miles and I seem to be getting no transmission. The set is on full power at these times, and was highlighted yesterday when Col tried to call me. I guess he was around St Olaves, and we were just past Cantley, so not a huge distance. I could hear him clear as a bell, but he was getting nothing from me at all.

My aerial is dead vertical and around 7' long so should be in the right position. There is a joint in the cable just under the radar arch that I had to remake, but I would have thought if this was playing up it would affect the Rx as well as the Tx. I would point out that I am going to fit a DSC set in the near future, but was intending to keep the old one for backup. It seems as though this might not be reliable though.

Any thoughts?

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Couple of things to check, is the power cable cleanly jointed and of the right cross section, an issue there would allow reception where little current is needed but on 25w transmit could reduce the power. You can check that fairly simply by putting your multi meter across the terminals at the set and seeing what drop you get on transmit. All antenna connections and cable should be of good quality, the joints well made and clean.

It could be worth getting somebody with an SWAR meter to check the setup as at that age, water can have penetrated coax joints and caused corrosion and high resistances.

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Morning Mark,

If you are not in too much of a rush to get it sorted, I have a good quality Power/SWR meter we can hook up to it. That way, we can check the condition of your antenna and also verify that you are getting 25 watts out of the tranceiver.

I will be at Swardeston later this week and could pop over to Brundall in the afternoon.

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Morning Mark,

If you are not in too much of a rush to get it sorted, I have a good quality Power/SWR meter we can hook up to it. That way, we can check the condition of your antenna and also verify that you are getting 25 watts out of the tranceiver.

I will be at Swardeston later this week and could pop over to Brundall in the afternoon.

What a wonderful forum this is, or rather, what a wonderful bunch of people populate it. :grin:

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Morning Mark,

If you are not in too much of a rush to get it sorted, I have a good quality Power/SWR meter we can hook up to it. That way, we can check the condition of your antenna and also verify that you are getting 25 watts out of the tranceiver.

I will be at Swardeston later this week and could pop over to Brundall in the afternoon.

That'd would be really helpful Jim thanks. I'll pm you my mobile number.

I'll also check the power drop on the battery cables as David has suggested, but as the radio is a Sealine original fit, I don't think cable size would be an issue, but could more likely be corrosion in connections.

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David is correct, as the VSWR meters for CB are designed to work in the HF band, and primarily around 27MHz.

A point to note, is that even a VSWR (Voltage Standing Wave Ratio) Meter, designed for use and VHF/UHF will only be "accurate", if it sees a 50 Ohm resistive (not reactive) load on the output side of the meter.

Your VHF radio is designed to work into a 50 Ohm impedance, and a correcly designed and installed antenna will present something close to this to the radio, which will then, assuming the radio is working properly, deliver its full rated output (.e.g. 25 Watts) to the antenna.

A pertfect match between radio and antenna would show a VSWR of 1:1. If the match is poor (bad or corroded joints, water ingress into the coax or antenna connection, or faulty antenna) the VSWR will rise accordingly (a high VSWR), which means that much of the output power is reflected back to the transmitter, which can damage the output transistor(s). A VSWR of to 2:1 should sensibly be considered the maximum acceptable, but of course, the lower the better.

David is also correct about using the correct wire gauge to power the radio, as if this is too small, the voltage drop when transmitting on full power would be significant.

I have a good quality VHF/UHF VSWR and Power Meter, plus a 50 Ohm dummy load, capable of comfortably handling the full 25W output of the transmitter.

Jim may well be able top assess and sort the problem for you, but if needed, I'm very happy to assist, albeit I'm down at the WRC, and don't know whether you are down south, or up north?.

Dave

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Thanks Dave and as far as I know, I should be able to check out the problem this Friday and hopefully not give Mark any bad news :wave

Are you into radio as an amateur Dave or where you involved in the business in the past? cheersbar

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Are you into radio as an amateur Dave or where you involved in the business in the past? cheersbar

Hi Jim

Have been a Class A radio amateur for over 40 years, taught radio at night school, and am a retired RF/EMC consultant engineer. So yes, I have played around with a bit of radio in my time ;)

Dave

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Hi Dave,

I thought you had a good deal of know how :wave PMR or PBR as it now seems to be known, is still a largish part of the business I run. I got involved with the radio industry back in the 70's and learnt the hard way way before cellular arrived. SWMBO was also involved in the old fashioned "message handling" industry business cheersbar

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That's very interesting Jim, and I'm sure we could enjoy a chat over a beer at some time cheers

When we moved up to Suffolk, 25 years ago, my wife worked 'part-time' for a PMR 'hire/supply' company in Ipswich. :)

BTW, is the 'Crazy Pub' still around where you live?. We used to drive out there in our courting days, back in the early 60's :lol:

Dave

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was that the pub with the " Largest water Otter in the world 50 years ago ?

Roy,

I remember that as being a pub called The Owl at Lippits Hill, on the way up from Sewardstone Road to High Beach. :)

Jim,

Its a shame that the old Crazy Pub is no longer, it was a 'one off', and holds fond memorys of some good evenings spent there.

I reckon we were last up there about 48 years ago :o

Dave

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Thank you for the offer of help Dave, it is greatly appreciated. We'll see what transpires when Jim tries to check it for me, but as I am based down south, a trip to WRC is always a distinct possibilty every now and then :grin:

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The Crazy Pub is what everyone remembers this area by, even though it is two villages south of us. When we moved here 30 years ago it was in decline because the landlady had become ill I believe and shortly after that, it closed for good. Does your good lady remember the "fig leaf" on the figure of the male mannequin in the ladies I wonder? :mrgreen:

If you Google the Crazy Pub, there are a few interesting articles on it including some pics from years ago. I never knew the pub got relocated from its original spot when they built Hunsdon Airfield during WW2 and story goes it was popular with pilots and aircrew during the war years. If I remember right, Hunsdon was a Mosquito base then and all that is left of the airfield is now used for microlights.

LOL what has this got to do with VHF I ask...Good old Fred Drift is having a field day cheers

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Thanks Dave the pub I knew was in the Hadhams and you pulled the chain in the well and up came a massive kettle! :dance now I stopped you all wondering about the "OTTER " .The pub we did use most in the area was the Hoops ,the publican Arthur provided most of us with memorable pre wedding Stag Nights :party2: .Ah those were the days ,now its Dublin or Prague or somewhere equally exotic. cheersbar

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you pulled the chain in the well and up came a massive kettle!

Must have been a common theme is those parts Roy, as it was exactly the same at the Owl :lol:

Jim, Mrs S says she doesn't remember the 'fig leaf', but it was a long time ago :lol:

Dave

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Many many thanks to Jim for coming to Brundall today with his metre. It seems my VHF is putting out absolutley nothing in the way of transmit power, which is why my range is down to about 100 yds!

By coincidence, when we put the unit back where it should be (in a locker) it now fails to turn on at all, so there was obviously something rather amiss inside the box!

Time for a DSC set then :clap

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