Problems with TX and RX mismatch

[safito]

Hi everyone I need some enlightenment cause I'm kind if lost. I own a couple of a 5 watts walkies dual band. I had installed a ST4 discone antenna.

When I transmit over, my friend at 4 miles away is able to receive really neat, but when He replies back I don't get any signals , I placed another walkie with a rubber duck antenna (14 inch) and the device is able to open the squelch however not really clear but at least it senses the the signal.

If I reply him through the rubber duck He hears the signal with a lot of noise.

So how come I'm able to transmit through the discone really neat but not able to pick up the signal?

My discone antenna has a 50 feet rg8x feed line


The 3 devices are clones so software setup is not an issue.

If signal loss is an issue how come it affects the RX but not the TX? Or it should be both?

 

[mikewazowski]

Thread moved to Amateur Radio Antenna forum since I assume you are using amateur radios?

 

[safito]

Yes sir, on both uhf/vhf.

Today I Ran another test where I hit the repeater to hear the queue, If I hit it with the discone the repeater reply is quite noisy, but the handheld with the rubber duck hears the repeater without the noise, however the handheld with the rubber duck is not able to hit the repeater...

 

[n5ims]

My discone antenna has a 50 feet rg8x feed line

That's your problem right there. RG-8X is VERY lossy at VHF and UHF frequencies. It was designed for HF. Get some RG-8 (note the missing 'X') which will be about half an inch in diameter and you'll have much better results. Even better, get some LMR-400 or better.

If signal loss is an issue how come it affects the RX but not the TX? Or it should be both?

It affects both RX and TX equally, but the starting power levels are much different so your apparent results are different. TX you start out with 5 watts (based on your post) so at the end of your coax, you have half a watt or so. On RX, you start out with millivolts and from the loss you end up with microvolts (too low for your radio to detect).

 

[safito]

Thanks mate, I'm going to get the lmr400.. I just wanted a confirmation on this.

 

[eaf1956]

Coax

You might want to try a better antenna than a discone. Try a dual band J pole if nothing else.

 

[prcguy]

RG-8X has about 2dB loss for 50ft at VHF and about 4dB loss at UHF, that's noticeable but not to the extent the OP describes. Especially if the Discone antenna is up in the clear.

I think something else is wrong like improperly installed or shorted/open connectors, etc. I would take it in steps and test or substitute the coax, try the rubber duck at the end of the coax, especially if it can be tested up high where the Discone is mounted and finally try the handheld with rubber antenna up where the Discone lives.
prcguy

That's your problem right there. RG-8X is VERY lossy at VHF and UHF frequencies. It was designed for HF. Get some RG-8 (note the missing 'X') which will be about half an inch in diameter and you'll have much better results. Even better, get some LMR-400 or better.



It affects both RX and TX equally, but the starting power levels are much different so your apparent results are different. TX you start out with 5 watts (based on your post) so at the end of your coax, you have half a watt or so. On RX, you start out with millivolts and from the loss you end up with microvolts (too low for your radio to detect).

 

[safito]

From the pl-259 to the walkie I'm using a reductor from pl-259 to a female sma connector, :

http://www.amazon.com/gp/product/B00COKNKS8/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

I was also wondering if the corrogated metal roof plus the metal mast maybe shorting electrically the antenna? I'm planning this saturday to add some insulator like a 3m electrical tape to the pl-259 antenna conector. However if there is a shortage how come the TX is not affected?

 

[N1BHH]

From the pl-259 to the walkie I'm using a reductor from pl-259 to a female sma connector, :

Amazon.com: DHT Handheld Antenna Cable for Wouxun Baofeng Quasheng Linton - Adapter for UHF Base and Mobile Antennas - SMA Female to UHF SO-239 Female Connectors 6'': Computers & Accessories

I was also wondering if the corrogated metal roof plus the metal mast maybe shorting electrically the antenna? I'm planning this saturday to add some insulator like a 3m electrical tape to the pl-259 antenna conector. However if there is a shortage how come the TX is not affected?

I wouldn't worry about insertion loss with adapters, there is next to zero difference. Always check to see if there might be a short, just put an ohm meter across the tip and shield of your coax. And I've been doing this a very long time, what do you think the tape will do? Nothing, don't insulate, that won't help at all. The roofing would actually be a plus, too, very good ground plane.

 

[safito]

Thank you Sir for the tip, I just tested for conductivity with a tester, and there isn't nor the conector, so everything is fine.

From the logical stand point I think n5ims has nailed.

It affects both RX and TX equally, but the starting power levels are much different so your apparent results are different. TX you start out with 5 watts (based on your post) so at the end of your coax, you have half a watt or so. On RX, you start out with millivolts and from the loss you end up with microvolts (too low for your radio to detect).

I'll double check on saturday if I missed something, perhaps the connector didn't went all through the antenna, or something else.

I'll try to get in hold of a 3 feet cable and check from the roof.

If someone else has another troubleshooting steps I should take bring them on they're always welcome.

I don't have a SWR tester, I only have a DVB-T ubs stick I wonder if there any application that can run in the computer with that to check for SWR measurements.

Also I was reading somewhere else that removing the whip from the discone it may improve the reception.

 

[KA9QPN]

A discone is a lot like a Swiss Army knife. It does a lot of things, but none of them very well. There is no gain to be had with it. Add lossy feedline, and you have a roof mounted dummy load. I use a discone fed with LMR-400 for my scanner and nothing else. There are a lot of nice and inexpensive dual band Amateur antennas to be had. Put different feedline on the discone and hold it aside for your scanner.