- Joined
- Dec 8, 2007
- Messages
- 87
Looking for an Isolation Tee to test for Desense. Anyone know where a person may find one?
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Looking for a Iso-Tee
- Thread starter emtunderwood
- Start date
prcguy
Member
What frequency range? Do you have a Bird 43 meter? If so this would work but its better to use a directional coupler for testing repeater desense. Ideally you find a high power version that can go in the antenna line then point the coupler back towards the duplexer and inject your weak rx signal. You can also get a generic directional coupler with 20-30dB coupling and place that in the duplexer to receiver line and inject the weak signal there.
- Joined
- Dec 8, 2007
- Messages
- 87
Yes I have a bird 43 meter.
prcguy
Member
Then the Bird sampler on fleabay will work in the antenna line or receiver line.
AS shown above thats a better solution but for quick tests the Unidapt works.
Unidapt RF Sampler Tee With N Male And Female Connector
Check out the deal on Unidapt RF Sampler Tee With N Male And Female Connector at Fieldcomponents.com
fieldcomponents.com
prcguy
Member
Here are various things I've used for desense testing and the Unidapt above is fine in the antenna or rx line. My preference is the Bird or Dielectric brand directional coupler slug in the upper left of the first pic or a high power directional coupler and the reason is it will send the weak receive signal only in the direction of the receiver and not to the receiver and antenna simultaneously like a simple sampler will. It will also couple less transmit power into your signal generator because the reverse coupling is usually a very high value like 50-60dB or more. A sampler set to high coupling can couple an amount of your transmitter power back to your signal generator and for example a 20dB coupler setting on a 100 watt repeater would couple 1 watt into your signal generator.
The two MiniCircuits couplers in the bottom of the first picture are directional with one being dual directional. With that one you can inject rx signals and sample what's coming from the antenna simultaneously. Or if you accidently hooked it up backwards just use the other coupled port. I like to terminate my coupled ports with an attenuator to increase the coupling value and give a nice resistive load to the signal generator.
The bottom picture is a Bird line sampler section you can attach to most any Bird product and leave it in line. Its not directional but will allow you to inject signals into the coax or sample a transmitter to feed to a freq counter or spectrum analyzer.
The two MiniCircuits couplers in the bottom of the first picture are directional with one being dual directional. With that one you can inject rx signals and sample what's coming from the antenna simultaneously. Or if you accidently hooked it up backwards just use the other coupled port. I like to terminate my coupled ports with an attenuator to increase the coupling value and give a nice resistive load to the signal generator.
The bottom picture is a Bird line sampler section you can attach to most any Bird product and leave it in line. Its not directional but will allow you to inject signals into the coax or sample a transmitter to feed to a freq counter or spectrum analyzer.
Ubbe
Member
One thing to look out for are RF leakage. But first it is important to not have too much of the TX power go to the signal generator as it could limit the RF signal level out from it and you then mistake it for the radio receiver to be desensing.
If the receiver can be set to analog mode then use a low modulated, maybe 1-2KHz FM, with a 1000Hz tone at a RF level where the smooth background noise starts to transition to have some occasional gunshots in its audio. That will usually be the 12dB SINAD level.
Then when at full TX power hold your hands around connectors and along the way of coaxes while listen to the audio if the noise level changes. Then you have some RF leakage that needs to be taken care of first before any tuning attempts are being done.
If the receiver are a digital mode only then you have to look at its bit error rate and that are more difficult as it always are a delay until the value are shown and you'll see if your actions made any difference.
If you need to use a high attenuated iso-tee in the 50-60dB range then do that hands on check without any TX power to see that the measurements are not compromised from RF leakage out from a poorly shielded RF instrument, it could have broken ground connections if it is a field instrument that gets tossed around a lot.
/Ubbe
If the receiver can be set to analog mode then use a low modulated, maybe 1-2KHz FM, with a 1000Hz tone at a RF level where the smooth background noise starts to transition to have some occasional gunshots in its audio. That will usually be the 12dB SINAD level.
Then when at full TX power hold your hands around connectors and along the way of coaxes while listen to the audio if the noise level changes. Then you have some RF leakage that needs to be taken care of first before any tuning attempts are being done.
If the receiver are a digital mode only then you have to look at its bit error rate and that are more difficult as it always are a delay until the value are shown and you'll see if your actions made any difference.
If you need to use a high attenuated iso-tee in the 50-60dB range then do that hands on check without any TX power to see that the measurements are not compromised from RF leakage out from a poorly shielded RF instrument, it could have broken ground connections if it is a field instrument that gets tossed around a lot.
/Ubbe
