Thread: HF troubleshooting

Check antenna earthing.

Is the manual tap in the correct band for frequency you are using ?

Thanks - that may have been an issue. I thought the earth was solid, and it tested ok with a meter, but I ran earth strap straight to the battery - which is less than a metre away from it and at this afternoons AULRO callback, I was heard in Northern NSW, QLD and WA, although very sketchy. I struggled to hear anyone else. I may be on the right track. I'll listen in on a couple of skeds and see how I go.

The antenna has all the right taps for what I need - VKS channels and a few others.

Put a dummy load on the coax at the antenna end. If all goes well you will have eliminated the cable. If not ...


Then, if the cable is proven OK you need to look carefully at the antenna. Connect a multimeter on the ohms (resistance) range and connect one lead to the centre of the connector at the base of the antenna. Connect the other end to each of the tap points in turn starting from the bottom. If the reading is about zero and doesn't change when you subject the antenna to a bit of vibration, move to the next higher tap. This will show if there is an antenna problem.


If neither show any issues come back with the details so we can see what else might help.


Howard

Forgive my ignorance, but what dummy load do I attach to the coax? I understand the testing of the antenna, but not that bit.

A dummy load is usually a wire wound resistor of 50 ohms value and of suitable wattage to take the output power of the transmitter ie if your transmitter is 100watts output the resistor should be able to handle that power. Secondly the resistor is submersed in a container of transformer oil to dissipate the heat generated. If your coax is ok you should get an SWR of zero. If you get a reading well above that your coax is probably faulty, or possibly the actual radio, but generally the coax. You can build your own dummy load provided you get the appropriate components, but they are a good thing to have for eliminating problems. You connect it via a coax socket so239 on the top of the container. You could use a large milo can etc. Jim

As he said. It looks like a perfect antenna to the radio.


You can buy some that can handle a 100 Watt transmitter such as yours for a short transmission that are quite cheap and use an aluminium fin for cooling.


If you are in Melbourne try Strictly Ham at Bayswater. Also check eBay.


It will probably have a PL239 alias UHF plug so you will probably need an SO239 to SO239adapter to connect it to the aerial end of your coax.


You won't use a dummy load often but they are useful bits to have around.


Howard

Could still be antenna earthing, 0 ohms with a multimeter will tell you nothing about earthing at radio frequencies. RF is funny stuff, you need a short heavy cable (battery earth braid is ideal) from the antenna mount to the CHASSIS of the vehicle. Not the battery. And the connections need to be shiny clean and decent size bolts used (~10 mm).
The chassis or body is the ground plane for the antenna.

Cheers,
Terry

I have a dummy load you can use if you still need one. What Frequency range is the radio on. I'll see if I have a Bird meter that can work at lower freq. to check the VSWR. What antenna plug does it uses, I'll have to make an addapter.

Let me know what you need and can give you a hand.