Diamond SG-M803 - faulty?

[VK3ANZ]

Having recently moved to a new QTH, I was wanting to put up an antenna quickly to get me back into operation. I had a Diamond SG-M803 (tri-band 2/70/23) antenna that I've not really used before (I was using it on 23cm and put down my lack of success to my location).

When I tried to use it, I found that I received nothing, and the "noise floor" (as seen via an SDR display) seemed to be unaltered whether the aerial was attached or not.

Using a DMM, I measure continuity between the ground part of the plug all along the antenna itself. Also I measure an open circuit from the centre connector of the plug to any other part of the antenna.

Thinking that there may be an internal series capacitor, I measured the capacitance between the pin and the body of the plug but it was really indistinguishable from the "open lead" capacitance measured by the DMM.

I am not familiar with the internal construction of these antennae (and I can't find anything via Google) but it seems to me that I should NOT be seeing the measurements I describe above.

Can some kind soul let me now if what I'm seeing is to be expected with these antenna or if I've got a "dud" one?

73

Susan VK3ANZ

[VK2AAH]

Hi Susan,

Do you know of anyone with an antenna analyser? If you can get them to check the SWR or return loss versus distance you can then work out where the fault is. Hopefully it is at the connector.

Cheers


Richard
VK2AAH

[vk1da]

Some useful indications would be found with any swr meter. If the antenna is open circuited at the connector as it seems, this would be revealed as a very high VSWR. This might be a quick and easy starting point. Comparing it with a quarter wave dipole built from plain wire soldered to the centre pin and body of a coax socket would also be worth doing.


Andrew Davis VK1DA & VK2UH
Sent using Tapatalk

[VK2EM]

Hello Susan

From the Diamond specifications, the following characteristics apply...

Diamond SG-M803 N

144/430/1200MHz(2m/70m/23cm)
Gain:2.15dBi (430MHz), 5.5dBi(1200MHz) / Max: power rating 60W (Total) / Impedance:50ohms
VSWR Less than:1.5:1, Length:0.37m / Weight:135g / Connector:M(SG-M803M), N(SG-M803N)
Type:1/4wave(144MHz), 1/2wave radialless(430MHz )/ 2x5 /8wave radialless(1200MHz )


Normally with this type of vertical antenna, the centre pin of the connector goes to a matching coil which is connected to ground, and the vertical is tapped onto the matching coil.

Whether the arrangement has a coupling capacitor somewhere, is problematical; but, according to the specifications, the VSWR should be "Less than 1.5:1".

So, if the SWR is greater than 1.5:1 on any (or all) band/s, you may probably regard it as faulty.

Hope this helps...

73
Bruce VK2EM

[VK3ANZ]

Thanks for the suggestions guys.

As I mentioned, I've just moved to a new QTH and most of my gear is still in storage. The only SWR meter I have is built in to my IC-9100 and I'll have to wait a little before I can dig that out. However it sounds like that is what I'll needs to do.

Cheers

Susan