Jumper-cable that did not work

[RF23]

I was trying to increase the signal strength of a 851 MHz control channel when using my Scanntenna ST-2 with 50 feet of RG-6 Coaxial cable in the attic of a single story house. I would usually get a 2 bars signal strength but often with the second bar flickering. This is not a very strong signal so on some days I could lose the control channel for a few hours.

To increase the signal strength I purchased a Wilson 700 – 960 MHz 8 element Yagi beam (Model 301111) and hooked up my 386XT using TRENDnet low loss Reverse SMA to N-Type 2 meter cable (N connector at one end and an SMA connector at the other so no adapters were needed). To my disappointment my 396XT showed NO signal bars. However, when I used 50 feet of Wilson LMR-400 coaxial cable with N-Type connectors I got a solid 5 bars (maximum possible) with no flickering.

The Yagi was only mounted 6 feet up from the ground and even indoors I still got 4 bars signal strength with no flicker.

The TRENDnet (TEW L202) jumper was designed to be used to extend the range of Wi-Fi (2.5 to 5 GHz) so I thought it would work well at 850 MHz but I guess I was wrong, unless I got a bad cable. The cable is very small in diameter about half the size of a pencil or less.

Anyone else every try to use this type of cable for the 700 to 900 MHz range?

 

[LtDoc]

How long was that jumper?
- 'Doc

 

[RF23]

The jumper cable was 2 meters long.

 

[rbm]

Isn't that TEW L202 cable reverse polarity (RP)? (No center pin sticking out)


Rich

Edit: It IS reverse polarity, so it won't work. The center conductors are not connected.
Many, if not most SMA connectors for WiFi are reverse polarity. (aka: RP)

"The low loss Reverse SMA to N-Type Cable extends your wireless"
TRENDnet | Products | TEW-L202 | Low Loss Reverse SMA to N-Type Cable.

Edit again" You can get adapters from one to the other on Ebay for a few bucks.

 

[GTR8000]

Edit: It IS reverse polarity, so it won't work. The center conductors are not connected.
Many, if not most SMA connectors for WiFi are reverse polarity. (aka: RP)

Ding ding ding...we have a winner!

If you look inside the RP-SMA connector, you'll notice that there is no center pin, which means there is nothing making physically contact between the coax and the scanner...just the ground.

You either need an adapter to get from the RP-SMA to a "normal" polarity SMA, or you'll need to replace that jumper with one that has the proper connectors for your application.

 

[RF23]

Thanks Guys for such prompt replies.

I did not see anywhere at the site that I purchased it from or on the box it came in that it was RP but now that I have checked it out, it certainly is. The adapter to fix this problem is on the way and was with tax and shipping only $6.00.

Now if the shielding is any good I may still be able to use it (it is made in China and will be fairly close to a computer). I only paid $15.00 for it so I cannot lose much but I now know more than I did (that is worth something) and as the old saying goes, being in a hurry and ignorant is a bad combination.

Thanks again for the very helpful information!

 

[LtDoc]

And as an aside...
If that cable is the same relative size as the SMA's end, it's probably something like RG-174 cable. That stuff is NOT for use on 800 Mhz, it contributes more resistance losses than anything. That can be good in that the apparent match will seem nice, but it's an absolute loss, terrible for passing signals at UHF.
I may have a totally wrong idea of what you are talking about so take that with lots of 'salt', you know?
RG-174 size cable get's worse as the frequency of use get's higher. It is only adequate for very short runs and lower frequency stuff.
- 'Doc

 

[RF23]

I agree and it is going to be interesting to see just how this thin coaxial cable does at 800 MHz even though it is designed for 2.5 to 5 GHz with a cutoff of 35 GHz. It may mean that in the GHz range the RF may travel differently along the coax and the cable may be as described a low loss cable, but I am thinking the same as you it may be terrible at 800 MHz. However, we will soon find out and I will let you guys know if it works and how well.

Thanks for taking the time to share this info with me and right now I am betting you are probably correct.

 

[rbm]

While I certainly wouldn't recommend long runs of small cable ........

I use a number of 18" (BNC to SMA) jumpers made with RG316 cable for use with my USB dongles and my BCD396's.

They prevent any strain or torque at the antenna connections and work just fine in very short lengths.

On 1090 MHz I can receive aircraft ADS-B signals more than 200 miles away.

RG316 has around 38 dB loss at 1000 MHz per 100' so ......................
My 18" jumpers, ignoring connector loss, will reduce the signals at 1000 MHz by a whopping 0.6 dB
That's something I can 'live' with.

Rich

I hesitated to mention this, but here it is .....................
I helped someone locally with the problem of SMA-RP to normal SMA connectors a while back.
If you're careful, you can cut a piece of thin wire exactly 11 mm long. Insert it into the center contact of one connector, and then into the other.
That should work temporarily to get you going. Just be very careful while doing it. It will create an impedance 'bump', but for a scanner, that's not such a big deal.

Edit: By the way, RG-174 loss at 1000 MHz is around 32 dB per 100'
http://www.google.com/url?sa=t&rct=...eyBc2ie2m_ES_X3TEoyEF8Q&bvm=bv.56643336,d.dmg

 

[RF23]

Well, this is certainly good news as this was my problem and the reason I ordered the jumper. Namely the LMR 400 is single stranded since it will be pointed in only one direction and is therefore stiff. My 396T, 396XT, and HP-1 are like a tail on a dog. However, I only use the SMA – BNC “broad-shouldered” adapter that Uniden sent with the radios so most of the cable stress is applied to the plastic case and not the SMA connector, which I think is attached directly to the circuit board. I have some SMA-BNC adapters that are “Stress City” to the connector in my opinion.

My 996T handles the stiff cable pretty well but I do not have room for it where I need to put the radio and I definitely do not like bending single stranded coaxial cable very much as I have seen them ruined by such maneuvers.

Unfortunately, I just got an e-mail from the company I order the adapter from and it seems they have the jumper adapter on “back order” and it will be the middle of December to early January before it will be available, but I think I can wait. However, if I can't wait I may give your "temporary" work-around a go.

Thanks for the help it is appreciated.

 

[RF23]

UPDATE:

Just received the adapter today (way earlier than expected) and it is only about 4 inches long.

Using the 8 element yagi at 7 feet up (indoors) and 50 ft. of LMR 400 I was getting two bars signal strength on the HP-1 (with the 2nd bar flickering a bit) and under "Trunked System Analyzer" and System Load / Reception Status screen I had ONLY a thin red line at the very bottom of the red vertical signal strength indicator.

When I removed the 50 ft. of LMR 400 and hooked the adapter to the 2 meter cable described in previous posts in this thread (directly to the beam) I then got three solid bars on the HP-1 and 3.5 to 4 on the red bar graph under System status. This was a much bigger increase than I expected.

Of course, the 50 ft. of LMR 400 would allow me to mount Yagi on the roof where no doubt the signal strength would be even greater.

So, I am please with the results but if you guys had not told me what was wrong I may have thrown the 2 meter jumper cable away, instead of finding out I needed to buy an adapter to fix the problem, so thanks again.