Running VHF and SSB antennae cables together.

[AndrewB]

It would be convenient to run my VHF and SSB antennae cables side by side for most of their length. Both cables are coaxial. Is this likely to cause reception problems? Would it matter even if the SSB and VHF are not switched on at the same time?

 

[bruce]

if your cables/coax are in good condition there should be no problem, but don't put antennas close together as they may effect signal radiation/direction.

 

[steverow]

No, no problem at all.

There may be some desensitisation of VHF when actually tranmitting on HF/MF but not enough I would have thought to cause an issue.

Steve.

 

[BlueSkyNick]

The only chance of any noticeable interference from one cable to the other, would be if you using both sets at the same time. For example, if you were to listening on VHF, and transmitting on SSB, which is only a hypothetical situation, IMO.

Therefore, nothing to worry about.

 

[AndrewB]

Many thanks for the reassurance, guys - that makes things a little simpler. I have a masthead VHF ariel and am using an insulated backstay for the SSB radio, both cables will be run up a mast conduit.

I'm going to have a lot of good quality 50ohm impedance cable left over, if anyone is interested.

 

[Bergman]

Re: Errr

Not sure why SSB cable is running up mast

I would have thought it goes to ATU near bottom of backstay.

From ATU to backstay should'nt be coax but heavily insulated single conductor which connects to stay.

Or am I missing something - apart from my aerial which is in a tangle of mast and wire on the ground.

 

[jerryat]

Re: Errr

Agreed. The connection to the insulated backstay should be from the ATU, ideally sited under the deck at the transom, and as short as practicable. Using co-ax for this connection is perfectly ok PROVIDED that you use use only the inner core OR the outer braid twisted to a 'single' wire, NOT both!

The latter is what I have used for years (more copper sectional area) was on the recommendation of several HF installers and has worked perfectly.

Cheers Jerry

 

[steverow]

Re: Errr

Yep agree with the above two posts.
Why are you running your HF/MF feeder up the mast when all that is required is the shortest possible connection from the Antenna tuner to the insulated backstay.
The only possible reason for doing this is if you are using either an inverted Vee or an "L" antenna, which is quite rare on a boat unless you are a radio amateur.
The tuner should be located as close as possible to the antenna.
So I would feed the backstay from the bottom not the top.

Steve.

 

[Guest]

Post deleted by danfoley

 

[Strathglass]

/forums/images/graemlins/confused.gif Like the others I don't understand.
From the photo of your yacht you appear to have two insulators on your backstay.

Any wire from your backstay to your ATU is part of the radiating element and cannot be passed down your mast.
The only place you should run a coaxial cable on your SSB setup should be between your ATU and the set itself.

You may have an SSB set with a built in ATU in that case all the wire from the backstay to the set is a radiator and cannot be a coaxial cable.

It would be nice if a sub minature tuner could be mounted at the masthead with a coax feed up the mast but technology has not reached there yet.

BTW. I will be using the centre conductor of very heavy coax for the feed from the lower end of the backstay to the ATU.
This has a 2mm silver plated wire with about 12mm of PTFE insulation round it.

Can you let us know what your setup is please?

Iain

 

[Bergman]

Re: Errr

Yes

That is possible but it would be a better arrangement to feed the bottom of a backstay on the mizzen and connect the top of the backstay to insulated triatic to form an inverted L antenna. This will give a portion of high angle propogation which can be useful for short to medium distance working which is often very difficult on MF and quite impossible on HF.

Perhaps you are thinking of trying to form a sort of dipole by feeding the triatic against the backstay. This is possible but it would need careful measurement to ensure both stays were the same length and even then would not be very efficient at low frequencies and would require a balun at the top of the mizzen to ensure a balanced feed point. It would also make the bottom of the backstay a high voltage point whatever frequency you were transmitting on.

 

[snowleopard]

as various others have said, it makes no sense to run an ssb cable up the mast. if it's a single cable to the antenna it is a radiating element and you would effectively be doubling back your antenna.

remember that MF/HF transmission is not line of sight so there's no benefit to placing the antenna high up, the reason for using backstays is to get enough length.

the coax from the set to the ATU radiates a fair amount, enough in my case to fry a nearby CO detector. the single conductor from ATU to antenna is a fully radiating element and is belting out 150 watts of RF energy which will transfer a lot of power to parallel cables. it's common to see every LED on a boat light up when transmitting and one boat i sailed on had to be hand steered as the autopilot went bananas.

so the safest rule for the ATU-antenna cable is to keep it short and keep it clear of anything else.

 

[AndrewB]

Thanks. Up to now I've used an SSB Rx only unit (Lowe HF150). This has worked very satisfactorily without an ATU, but as I'm now considering installing a Tx facility, this advice is much appreciated. The coax cable to the ariel has previously been attached at the bottom end of the backstay but this is a nuisance for several reasons. First, I've run out of below-decks wire conduit space and spare deck glands at the aft of the yacht. But there is a spare conduit leading to and up the mast with a gland through which the ariel cable could be rerouted. (Owners of steel boats will appreciate my reluctance for creating extra through-deck holes). Second, detaching the backstay for any reason (e.g craning out) has been complicated by having a wire attached 3m up the backstay, that has to be detached each time. Third, it looks rather untidy.

I had assumed that the shielding of the coax would prevent it acting as an extension to the ariel, since the core is the part actually connected, and therefore it would be possible to fit an ATU at the inboard end, immediately ahead of the SSB. An alternative, if such things exist, would be a small weatherproof ATU mounted at the masthead. There are fittings available there, from which it would be earthed.

 

[john_morris_uk]

The shielding of the coax will not "prevent the inner acting as an antenna" as you say. I am afreaid that you will have to put up with the 'untidy look of the spare bit of wire joining onto the backstay' to effect an effective installation.

A length of coax attached to the outlet of the ATU terminating in the 'antenna' part of the system will have odd effects on the impedence that the ATU is matching. Don't do it is my advice!

 

[Strathglass]

Andrew

Been doing some looking up.

Yes, there is an auto ATU which could possibly be mounted at the masthead but it costs £300 and weighs 0.9kG.
I certainly wouldn't want that weight at the top of my mast.
It also requires a 12 volt supply.

So it is possible to feed your backstay from the top with a coaxial feed down the mast. I imagine that perhaps the mast itself could be used at the counterpose thus minimizing the requirement fot a good earth.

Just some thoughts

Cheers

Iain