A smear of Vaseline?

Clive

I was fascinated to read about your maritime radio experiences. I was impressed by being able to work the UK from South Africa on a whip aerial at 10W, was that on the key or SSB?

It was particularly interesting as at waterproofing aerial systems as I am preparing to erect a new amateur radio HF aerial myself. I am going for an end fed 1/2 wave aerial. I have wound a 49.1 UnUN and put it in a plastic box. I am concerned about water getting in the box so thinking about putting it in my loft just inside the gutter board and then feeding the aerial out. I am also going to wind a choke to go at the end of the aerial to extend the coverage to the 3.5-3.8 MHz., I need to go to Screfix to get some 25mm plastic conduit for the core. The UnUn has a SO 239 socket which I will feed with a metre of RG 213 Co-Ax in to a common mode choke and then RG213 to a auto ATU (or should that be an AMU). I just need to put up a scaffold pole at the end of the garden to act as a mast. 

Conventional roof top T.V. aerials have a drain hole fitted at the lowest point in the plastic connector box in most cases. Can this be used on amateur radio equipment as well?

A drain hole prevents condensation build up and assists rain ingress removal.

Z.

That was a good read, and the linked schematics the AATU are interesting - monitoring antenna amps as well as forward and reverse power is a nice way to detect the condition where it finds a  match where all the power goes into setting fire to the  tuner itself (ah yes.. it really can happen) Glad you were able to jury rig a new inductor and keep it going.

Mike.

The same tricks are used but as ham radio has thin slices of the bands allocated at all sorts of frequencies, so antennas range from hundreds of metres long for VLF to sub millimeter for the microwavers and everything in between,

https://rsgb.org/main/operating/band-plans/

unlike the TV bands that are just UHF, the techniques have to vary with the scale.

Mike

(G7VZY)

watch the voltage peak at the end of the half wave - at that point the impedance is high, and you will need to  keep things away  if you are pushing reasonable power - RF burn and even ignition is possible.

Mike

Thanks the high voltage that may appear on the ends of the aerial is a concern of mine which is my dilemma of outside or inside. My Tx. output is max. 100W so high voltages could be an issue.

Thanks

JP

Hi John

Although licensed since the mid 70s as GW4EYO my only time on the air was from Riversdale College in Liverpool where early in my RO course I got examined for 12 wpm. Previously as GW8AOC I had been occasionally active on 2 metres and 70 cm.  Whether I will get the urge during retirement, I don't know. Problem is a suitable aerial and earth/ground plane arrangement.

Anyway, you mentioned an auto ATU. So do you need an UnUn to connect your end fed ½ wave to your auto ATU? The more so if there is a distance between the UnUn and the auto ATU.  I think it better to match the aerial to the feeder - 50 ohm coax - at the ATU, rather than using the auto ATU to match the transmitter into 50 ohm coax, use the PA Tune and Load for that at the transmitter. (The Skanti used three 250 watt wideband PAs https://www.qsl.net/p/pe2jeb//foto/Skanti_HF_TRP-8000/TRP-8750/626-631%20power%20amplifier%20board.pdf into a combiner which does not appear to be listed here https://www.qsl.net/p/pe2jeb//foto/Skanti_HF_TRP-8000/TRP-8750/ 

I noticed you mentioned a SO 239 socket. In my experience the SO-239 and PL-259 combination is not that weather proof, even the posh PL-259s with a built in gland. Type-N not much better. 

Although it makes disassembly difficult, I am a big believer in using adhesive lined heat-shrink sleeving.  A cheap electric hot air paint stripper is ideal (you can now get battery powered versions, in Lidl today! Battery extra, but it fits the range.)

My Cape Horn (Chile not South Africa) to UK was on Radiotelex. This used FSK by feeding the Skanti transceiver 1615Hz / 1785Hz and offsetting the suppressed carrier downwards by 1700Hz. 100 Baud using ARQ (sends 3 characters, waits for an acknowledgement or resend RQ and send either the next 3 or the same 3 characters. Overall 50 Baud which was the standard for Shoreside Telex. Audibly a sort of Zip, Zip, Zip sound with a FSK wobble.  It was a two frequency simplex system ie Ship and Portishead Radio on two separate frequencies.

It could be set up for Portishead Radio to call the ship when messages came in to them. This gave me some puzzlement/amusement since usually I would leave the system on Portishead's pre-notified channel with the speaker on low, whilst I was getting on with something else with my back to the control unit and screen. I then used to find myself turning round on my chair a couple of seconds before the transceiver would burst into life with an incoming message. Why was I doing this, or why was I able to anticipate the message? Was my brain capable of recognising the FSK for the ship's 5-digit Selcall number?? (This is a different system to aviation Selcal) Surely not.  Eventually it dawned on me. Very few, if any, other ships were availing themselves of an automatic incoming service. What I was reacting to was the slightly different cadence of the to-ship calling sequence. As simple as that. Fear of approaching madness over!

Clive

When I used to work for a living we used contact grease on terminals. I've just googled and there are still some products on the market.

We had some in a factory where I used to work, but it was lead based.

Z.

Morning Clive

I think I may have a solution to your problem of aan aerial in a restricted space.

I visited an amateur radio rally on Sunday in Bletchley. On the way in I saw a whip aerial sticking above everything else in the field. I saw this close up and spoke to the stallholder who was using it to demonstrate a transceiver he was selling and it was not for sale. He uses it for QRP working in the same field used by his club. It was a 17m telescopic whip that collapses to about 800mm mounted on a caravan TV dish collapsible tripod usually with a few 1/4 radials. He tunes it by sliding the aerial joints in and out. Co-ax from the stand to the rig and he says he can be up and running in about 10 mins from parking his car to being on the air. From the field he says he once worked Australia but had to increase the power form 5 to 10W. 

I have ordered up the 17m stainless steel whip and a tripod via eBay which should be with me this week. I will let you know how I get on.

If you want a chat about the details call me using the details from info(the symbol for at) astutetechnicalsrvices.co.uk.