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Old Mar 17, 2012, 07:16 AM
The Dreamer
Pisces's Avatar
Sydney, Australia
Joined Dec 2010
939 Posts
Hi Marcus,

Of course you are correct. The Vr is very small at VSWR less than 1.1. I have not used bias as the test is to compare with Jay build and tune and he did not use bias. Also it is a small % of the bandwidth for the 8 CH of the Vtx. Less than 5% of BW is tested.

I can re-do the test with bias on and also do a cal with 10dB att 20dB RL and VSWR 1.2. But I have previously reported these cal tests. Then there will be more correct readings for VSWR less than 1.2

I could also do the test using IBCrazy and a DMM but i know I will get the same result. Every time i do this check with a DMM I get the same result as with the AMM.

I did not post a DL cal but it is zero Vr and VSWR 1:1

I will post the VSWR I tested with the RP-SMA. This is the exact same test as above. See what I mean about RP-SMA. Jay tuned the pinwheel without RP-SMA.
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Old Mar 17, 2012, 07:35 AM
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Switzerland, LU, Buchrain
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Quote:
Originally Posted by Pisces View Post
Hi Marcus,

Of course you are correct. The Vr is very small at VSWR less than 1.1. I have not used bias as the test is to compare with Jay build and tune and he did not use bias. Also it is a small % of the bandwidth for the 8 CH of the Vtx. Less than 5% of BW is tested.

I can re-do the test with bias on and also do a cal with 10dB att 20dB RL and VSWR 1.2. But I have previously reported these cal tests. Then there will be more correct readings for VSWR less than 1.2

I could also do the test using IBCrazy and a DMM but i know I will get the same result. Every time i do this check with a DMM I get the same result as with the AMM.

I did not post a DL cal but it is zero Vr and VSWR 1:1

I will post the VSWR I tested with the RP-SMA. This is the exact same test as above. See what I mean about RP-SMA. Jay tuned the pinwheel without RP-SMA.
Pisces,

I have the highest respect for your great work. My comments centered on the antenna - not your meter. I'm building precission antennas as you surely know and I also know that most people lurking in these forums don't know enough to see the differences among antennas made and or offered. I just tried to point out that there is a general tradeoff between bandwidth of an antenna and return loss (SWR). We both know that no antenna can have an SWR of 1 across a wide frequency spectrum (several channels). But users seeing your antenna and mix this with terry's (understandeable euphory about the meter) will otherwise interprete the postings the wrong way. So guys, continue your great work on those meters, and I will continue building antennas

Cheers

Markus
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Old Mar 17, 2012, 08:12 AM
The Dreamer
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Sydney, Australia
Joined Dec 2010
939 Posts
Pinwheel Bias ON and OFF.

From my very early posts on the use of bias I have indicated that the benefit is at very low Vr where it overcomes the turn on step non-linearity of the detector schottky diode.

Also to note that VSWR 1.2 and less there are a number of uncertainties as to what is actually being read as VSWR.

Source Z
Reference Z
CAL Z
Coupler thru line
Connectors

Attach is a 10dB DC-18Ghz attenuator cal check

10dB Att with Bias OFF.close to VSWR1.0
10dB Att Bias ON VSWR 1.1

Pinwheel Bias off VSWR 1.0 (previous post but checked and not attached)
Pinwheel Bias ON VSWR 1.1

Bias improved the very low values of VSWR less than 1.2. I also believe that this the same result if bias was used with a DMM.

Also note the the mechanical zero is used with bias ON to re-zero the scale so that bias is not included in the VSWR measurement.

And Jay..how did you manage to get the pinwheel so perfect.. I cant get any near this good a result with my builds. I'm happy with VSWR 1.2 to 1.3

Lindsay
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Old Mar 17, 2012, 08:34 AM
The Dreamer
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Sydney, Australia
Joined Dec 2010
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Marcus,

No problem I understand. You have a VNA it is the best for doing this testing. I think the issue is the AMM (or DMM) and without bias. We are using a 6dB att so the 200mW (maybe less is CH dependent ) is only 50mW into the coupler.

At less than VSWR 1.2 the diode starts to become non-linear DCV out and maybe starting to cut off. I have noticed this with the att test with more than RL 20dB the Vr drops off and the att value RL is not read correctly..But is very low value and less than VSWR 1.2 there is some measurement uncertainty..

See above there is Vr with bias. Also the 10dB did not read exact value VSWR 1.2

Cant say any more about the pinwheel unless it is volunteered by Jay.

Marcus, I understand about not to mislead the group. Your points are valid and show up when I turn the bias on.

Lindsay
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Old Mar 17, 2012, 10:08 AM
la fabrique circulaire
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geneva
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...
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Old Mar 18, 2012, 08:21 PM
The Dreamer
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Sydney, Australia
Joined Dec 2010
939 Posts
Pinwheel VSWR test UT141 pin with Bias

Pinwheel Part 3 of the trio of VSWR test with AMM.

1 With RP-SMA adapter
2 With UT141 adapter PIN without BIAS
3. With UT141 adapter PIN with BIAS

This VSWR AMM test is with Bias and the UT141 PIN.

Also note how accurate the CAL att test is with BIAS.

Whoever build these Pinwheel needs a third opinion??!!.

AMM VSWR + Bird6000EX ( nice VSWR modern test set) + finally a wider bandwdth sweep on a S parameter test set or VNA .

Enjoy
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Old Mar 19, 2012, 02:00 PM
Always soldering
Joined Dec 2011
234 Posts
Nice tests Lindsay thanks for sharing!

I note that you improve your reference port termination with an att. I also get better results with BIAS on and the 12dB DC-12.4GHz attenuator and Dummy Load on the coupler.

This is allready posted on my tests also earlier on the thread...

I also build another SMA to SMA UT141 addapter with SMA no center pin connectors, shorter and builded more accurately, also this improve some my system.

EDIT : Note now that your VTx do have the Tantalum 47uF capacitor on it, mine doesnt have that one and others also report this here, I found a replacement on RS components and cost like 5 euros each one but only sell x 5 units.You are pretty lucky.

-Martin-
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Old Mar 19, 2012, 02:05 PM
la fabrique circulaire
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geneva
Joined Jan 2008
550 Posts
you didn't tell me it was a contest!!!

can I fly again?

I have a new challenge now that the PW 5.8 MK2 work well: I will have some try to stack 2 PW with O.M.M method (5/4-3/4 T on RG179 coax) ,for hoping a omni 5.5dB PW

nice to see that your Bias work really well when using good components (same here)
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Old Mar 19, 2012, 02:10 PM
Always soldering
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Nice Jay!

Looking forward to see your tests and foundings!

-Martin-
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Old Mar 19, 2012, 11:42 PM
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Upstate NY
Joined Jan 2008
200 Posts
Hey Guys, great stuff your working on here.

The data sheet says this diode is used without bias when Pin is above -20 dBm. With a 6dB attenuator dropping the input power to 50mW and 10 dB of coupling, it’s 5mW (500 mV) into the diode.

That is +27dBm over the -20dBm threshold listed for small signal detector applications. You do not need to bias the diode at +7 dBm.
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Old Mar 20, 2012, 04:03 AM
The Dreamer
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Sydney, Australia
Joined Dec 2010
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Quote:
Originally Posted by nysom View Post
Hey Guys, great stuff your working on here.

The data sheet says this diode is used without bias when Pin is above -20 dBm. With a 6dB attenuator dropping the input power to 50mW and 10 dB of coupling, it’s 5mW (500 mV) into the diode.

That is +27dBm over the -20dBm threshold listed for small signal detector applications. You do not need to bias the diode at +7 dBm.
Hi @nysom,

Did you consider in your calculations that we are measuring Vr (voltage reflected ) from the test load or antenna. We have a VSWR of 1.1 and less and this is the intention of using bias to improve the sensitivity of the schottky diode rectifier.

Maybe you can calculate for us the the Vr (voltage reflected) and calculate the dBm into the detector and read as DCV by the AMM when the VSWR of the test load is 1.1 or less.

Please advise what you calculate?. We are very interested to know why this test set up works so well.

Lindsay
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Old Mar 20, 2012, 05:42 AM
Registered User
Romania, Bucuresti, Bucharest
Joined Dec 2010
69 Posts
For small signal measurement Logarithmic amp. sensor work great for me. AD8318 has a very linear curve from -55db to 0 db. When I made measurement I put vtx(+23db), atenuator(-30db), directional coupler (-10db).
Total +23-30-10 db= -17db for full Vr power (no antenna)
With dummy load conected at output i have -45db
A 28db dynamic range is perfect for a DIY.
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Old Mar 20, 2012, 07:42 AM
Kiwi in Germany
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Germany
Joined Jun 2010
2,289 Posts
I need some advice. I have been looking into tuning my antennas. My problem is ... I think my meter is wrong as I get no reflected power i.e. 0.0v I tried 5885mhz and 5945mhz and get 0v in return while on 5705mhz I do get reflected voltage.

could I just have built my antennas well or is there most likely something wrong here?
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Old Mar 20, 2012, 08:22 AM
Always soldering
Joined Dec 2011
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@whakahere

I think that this is what we are talking about here.

Its about the sensitivity of the mw diode detector, just dont read anything when the Vr (good VSWR) is to low. This is why we are using BIAS in order to incresse the sensitivity at low VSWR.

I think that ones you get 0.0V on your Vr readings your antenna is OK but you cant know exactly how much OK it is! In simple words cause im just a simple newbie here.

So your antennas are better on the CHīs that you dont get any V reading. But off course this is not exactly 0.0V reflected. It is just that the diode cant read that very little Vr.Sure if you put an in-line 30 dB attenuator on your VTx surely you get 0.0V on all the CH.

Sounds pretty logic?? Or maybe not??

You build a lot of antennas and it is also normal to get some good ones with the skills you allready get doing all those builds. I THINK.

Anyway, sure you get a better answer from the experts here. Im just a instructions follower.

EDIT : Did you build your detector or is the Micīs one? Did you have a higher mW power VTx to try the same antennas?

Martin
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Old Mar 20, 2012, 08:33 AM
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Upstate NY
Joined Jan 2008
200 Posts
Hi Pisces, I am not going to do any further calculations as anything below 1.2:1 is less then 1% power loss and not worth the effort. Even at 1.3:1 the loss is 1.7% and that is 3mW.
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