SDS100/SDS200: "Stubby" SMA antenna 700/800

[N0GTG]

I'll second this recommendation; I picked up a couple of these at a hamfest a few years back and they work fine on strong systems. The only caveat is that the connector on the antenna was not deep enough to sit flush with the scanner I wanted to use it on (BCD396T), leaving a small gap between antenna base and the top of the scanner. Didn't affect functionality, but looked unpleasant. A trip to the hardware store got me a black rubber gasket that fits perfectly and eliminates the unsightly gap.

The 806SM is my standard antenna on my BCD396 and SDS-100. For the SDS, I took a sharp knife and cut off about 1/4" of the rubber on the bottom, and it fits just fine.

 

[billybob]

I have been searching all over for this adapter. Can someone point me where to buy?

Comet CH-32 and a custom sma-to-bnc adapter sold in the classifieds section of RadioReference.

View attachment 68692

 

[jjbond]

I have been searching all over for this adapter. Can someone point me where to buy?

They're no longer listed in the classifieds section... however... Here, let me Google that for you....

SMA/BNC ANTENNA ADAPTER x2 Uniden BCD396T BCD396XT SDS100 BCD436HP HOME PATROL | eBay

BNC to SMA Adapter – SDS100 – SILVER (Nickel) – Airspy.US

 

[N6ML]

Hmm. The AirSpy one is out of stock. The eBay one, I'm not sure about. It looks like it's flat on the bottom, which may or may not work well (screw in all the way, so the pin makes good contact) with the SDS100's connector, and the washer makes me even more skeptical. The one that was being sold on RR was machined to specifically fit the SDS100. I made my own, rather crudely, by putting one of the flat-bottom adapters in a drill press and using a file to "machine" the bottom to fit.

Here's my hacked one:

 

[billybob]

Thanks for your help. I thought the adapter sold on the classifieds were machined down to fit into the bevel at the antenna connector. I have an adapter enroute from a member who had a few on hand. Thanks

 

[RRR]

The SMA type antennas (that directly connect to the SDS100 via the SMA) are very easy to break. If the BNC adaptor is used, then you have some strength, but I have had 2 of the more well known, "custom SDS 100" antennas break at the SMA base already.

 

[cmdrwill]

Maybe that's the problem...there is no standard? It seems the majority of SMA antennas do not fit the Uniden SDS-100 properly.

And at even VHF frequencies, an 'adapter' will cause a mismatch as it affects the RF lenth of the antenna. And then there IS a difference in counterpoise or 'ground plane' with different scanners or hand held radios that will mess up antenna performance.

And most of these antennas are NOT very durable. But they are NOT handles.... either.

 

[W5JCK]

Scanner and HT rubber-duckies are frequently little more than dummy loads. That is especially true of the very short ones. You can tune pretty much anything for an antenna, including a barbed wire fence with the right equipment, but being tuned with a low SWR doesn't mean it will hear or propagate radio signals well. I have mentioned in other threads that rubber-duckies tend to be less than 1/2 wavelength, and as such they need a ground system. When you hold the scanner or HT your body becomes the ground half of the antenna. When you sit it on a desk then it likely won't have enough of a ground plane due to the small size of the radio chassis. A 1/4 wavelength antenna works fine as long as it has the ground half, but without that it won't be very good. You can hear strong signals even without an antenna installed, and honestly a lot of the rubber-duckies are not much better than having no antenna. Best practice is to get an antenna specifically designed for the band(s) you monitor and find one that is 1/2 wavelength or longer. With VHF that means a rather tall antenna of about 17"+, but with 800MHz it can be closer to 3.5". Those little shorties will probably work okay for 800MHz trunking as long as you are in near proximity of strong signals, but so will no antenna installed. However, on VHF they probably won't work well unless you are very close to a strong signal or at least in direct, unobstructed sight of the TX antenna.

 

[iMONITOR]

Scanner and HT rubber-duckies are frequently little more than dummy loads. That is especially true of the very short ones. You can tune pretty much anything for an antenna, including a barbed wire fence with the right equipment, but being tuned with a low SWR doesn't mean it will hear or propagate radio signals well. I have mentioned in other threads that rubber-duckies tend to be less than 1/2 wavelength, and as such they need a ground system. When you hold the scanner or HT your body becomes the ground half of the antenna. When you sit it on a desk then it likely won't have enough of a ground plane due to the small size of the radio chassis. A 1/4 wavelength antenna works fine as long as it has the ground half, but without that it won't be very good. You can hear strong signals even without an antenna installed, and honestly a lot of the rubber-duckies are not much better than having no antenna. Best practice is to get an antenna specifically designed for the band(s) you monitor and find one that is 1/2 wavelength or longer. With VHF that means a rather tall antenna of about 17"+, but with 800MHz it can be closer to 3.5". Those little shorties will probably work okay for 800MHz trunking as long as you are in near proximity of strong signals, but so will no antenna installed. However, on VHF they probably won't work well unless you are very close to a strong signal or at least in direct, unobstructed sight of the TX antenna.

I totally disagree. A dummy load is used to provide a load on a transmitter for testing purposes. A dummy load is not suppose to radiate a signal. Without exception all rubber-ducky antennas, even the shortest ones ever made radiate a signal and should never be used as a dummy load!

Rubber-ducky antennas are used more than anything else for antennas on hand-held transceivers, FRS, GMRS, MURS, Marine, Ham HT's all over the world, transmitting and receiving signals reliably. Just look at all the public service hand held radios used for life & death situations! Regarding VHF, look how many VHF/Hi and even VHF/Lo hand held radios use rubber-ducky antennas! Ever see the antenna on hand-held radios used by Fish & Game, Forest Rangers, Military, etc?

Using the Diamond CH-32 Miracle Baby antenna I can pick up 800MHz P25 systems reliably from over 12 miles away!

 

[jeffdafoe]

And at even VHF frequencies, an 'adapter' will cause a mismatch as it affects the RF lenth of the antenna. And then there IS a difference in counterpoise or 'ground plane' with different scanners or hand held radios that will mess up antenna performance.

Asking to understand, not an antenna expert by any means.. why does the adapter count as part of the antenna when it still carries the shielding.. wouldn't it be considered more as part of the "antenna cabling"?

 

[jeffdafoe]

Hmm. The AirSpy one is out of stock. The eBay one, I'm not sure about. It looks like it's flat on the bottom, which may or may not work well (screw in all the way, so the pin makes good contact) with the SDS100's connector, and the washer makes me even more skeptical. The one that was being sold on RR was machined to specifically fit the SDS100. I made my own, rather crudely, by putting one of the flat-bottom adapters in a drill press and using a file to "machine" the bottom to fit.

Here's my hacked one:

View attachment 71406

For my SDS100, I have one that I got off ebay months ago that is beveled like the one above. I checked and that seller doesn't have any in stock anymore. After reading this thread, I also ordered the flat bottom one for comparison. I just measured and the beveled one engages the SDS antenna connector's center pin more than the flat bottomed one. Both have six threads to the base of the SMA, but the bevel allows that particular adapter to seat the center pin in what is probably a more proper depth.

-Jeff