Dummy load

[Hair Bear]

Hi,
I'm looking for help trying to fault find on a base installation.
The background is, a shop standard Grandstand base rig one end, and an Antron 99 on the other. Inbetween there are several sections of coax (I know, I know...). The reason for this is the original build dates back to 1987 and at that time the lead was one length of RG213. This was over time incorporated into the house, chased under floors and under plaster, through walls etc. been in place for years. At each end the antenna got moved and rearranged several times and as the main coax was pretty permanent lengths were added as necessary, and likewise indoors the rig got moved around with coax added and changed as required. None of this appeared to affect the operation of the system - good swr and always checked with the built in swr meter for consistency.
Now for some reason there's no rx or tx, the swr has hit the end stop and I cant work out why. I've been through all of it checking for opens and shorts but nothing obvious. A handset right beside the rig shows rx and tx both ways, but at 3' I'd hope so.
So, to my question...
If I had a dummy load and placed it on the antenna end of the coax, or any of the coax connections, would that give a zero or close to zero swr showing the cable to that point is ok?

[NightProwler]

A dummy load on the antenna end of the coax should show you an SWR of zero unless the coax is knackered somewhere.

[Hair Bear]

Thanks, that was what I was hoping for. Could you suggest a suitable spec for a dummy load to obtain for this purpose?

[NightProwler]

As long as it's a 50ohm load and will handle what power you put into it then it will be fine. A 15 watt load will be ok as long as you don't put more than 15 watts into it. Make your own it's easy to do.

[Hair Bear]

What sort of components would be needed?

[NightProwler]

I use one of these connected to an S0239 and bolted to a heat sink. Works perfectly up to 250 watts

https://www.ebay.co.uk/itm/178015434525 ... 7527740450

[NightProwler]

Or one of these will do if you cant be bothered to make one...

https://www.ebay.co.uk/itm/267579680874 ... R7yXo_uFaA

[ch25]

A dummy load on the antenna end of the coax should show you an SWR of zero unless the coax is knackered somewhere.

SWR 0 does not exist in our world.
Chris

[Hair Bear]

Thanks, first time in more than 30 years it's failed me. I can normally find faults in mobiles quite quickly but this has stumped me.
I'll let you know how I get on, and what stupid simple thing I overlooked.
Cheers.

[Buick Mackane]

A dummy load on the antenna end of the coax should show you an SWR of zero unless the coax is knackered somewhere.

SWR 0 does not exist in our world.
Chris

Aye and neither does the tooth fairy, But there are those who still worship him And i don't think I'd be ramming 250 watts into that tiny Chinese sweat shop resistor

[NightProwler]

I dont but it's been fine chucking 100 into it.

[NightProwler]

A dummy load on the antenna end of the coax should show you an SWR of zero unless the coax is knackered somewhere.

SWR 0 does not exist in our world.
Chris

Gordon Bennett, Ok then a low SWAAAAAR

[Antoni]

Those bolt-on power resistors do work. I bought three of the power attenuator versions rated at 100W (-10dB). They work as advertised with a good match/atten at 100W continuous and work at 450MHz (beyond that the terminations let them down a bit but bloody useful alll the same).

I'd get one of those 250W jobs but I have a professional AF 150W one. If you do any work on radios or feeders a dummy load of some sort is a must.

[ch25]

@OP put dummy load instead of antenna and measure. You'll know if coax is OK or not.
VNA would be better, because you can also measure coax loss.
Chris