ADF4351 signal generator

Richard Lee

The output port of the directional coupler must be connected to a measurement device. I'm using a diode detector on mine. The diode feeds a DC voltmeter, to give me a relative measurement of the reflected power (SWR). It's really very crude, but works fine..

If you wanted to, you could connect the measurement port to a spectrum analyzer. Like this YouTube guy did..
If you are measuring 1090 Mhz antennas... Just use one of your RTL SDR sticks and get your return-loss measurements in dB off your computer display..You can make your generator sweep-step, and your PC will act like a spectrum analyzer.
It will show you where the antenna is resonating best..

One other thing you will need is a good 50 ohm load.. If you are using 75 ohm coax and testing 75 ohm antennas, get a 75 ohm load..
Before connecting your antenna to a test cable, install the dummy load on the end of the cable..
Just about 100% of the RF into the load will be absorbed (turned into heat).
So, the test port should be showing zero power out (or close to it) with the load installed..
Then remove the load and note the Return loss reading (it will be very high), before you install a test antenna..
The power reflected back(SWR-Return Loss) from that antenna will be flowing out the monitor port of the Directional Coupler. A really good antenna will look like the test load.

To make accurate measurements of Return Loss, you can reverse the RF in-out ports on your Coupler, and take a relative measurement in both directions. Then, do the math..
I never do it that way.. I just try to tune the antenna (or filter) to the lowest possible return loss and then test it for function. Comparing it to another (known good) antenna.. :)

Richard Lee

They should be okay. It will be easy enough to test them. :)
Just don't expect the really cheap ones to work very well up above 2 or 3 gHz.

I remember when Radio Shack was selling them made with a 1/2 watt 75 ohm resistor.
They stuck the resister into the connector body, folded the top wire over and soldered it to the connector (ground).
And used the other lead for the center conductor. Just clipped it off.
The problem was the resistor lead was soft copper wire and would sometimes bend when you plugged it in...
They did work.. Mostly..

Richard Lee

I just saw a nice little Frequency counter (IBQ101) for about 27 USD.
I does 50 mHz to 2.6 gHz. A few years ago, the price of this would have been Much higher..

Anyways, because this counter has a signal strength bar display, it can be used to measure the reflected power off the monitor port of the directional coupler.
Looking at the video, the signal bar seems to update pretty fast. That means you could just watch the bars move up and down, while you tweak the tuning..
Instant feedback is important when working with microwaves, when a tiny tweak can get you the perfect Z match..

I think the IBQ101 has a sensitivity of 15 microvolts above 1 gHz. So it should work okay.. If it's too sensitive, adding an attenuater will reduce it..
And if the output from your Directional Coupler is too weak, a little LNA will fix that..

I don't know what kind of antenna connector is on the IBQ101. So, you might need an adapter to connect it to your Directional Coupler.
In these pictures, it looks like a standard SMA..

ab cd

Senior Member
Thanks Richard for very useful information. Added IBQ101 Frequency Counter to my shopping list.

Richard Lee

It should work for a basic antenna testing set up.. Just won't go below 50 mHz..
So, it won't work for the shortwave radio antennas.
I have had a nice little portable counter for over 20 years.
It wasn't cheap back then, and it went all the way up to 1.5 gHz..
Not quite what we need these days.. :)

One of the other things you can do with that IBQ101, is use it in an open area to probe the RF field of a transmitting antenna.
In the right conditions, you can get a good idea of the width of the main gain lobes of directional antennas.
They are also used for finding RF bugs that may have been planted to spy on someone..

Been looking and I've seen a few portable counters that had specs that said 2.4 gHz..
Not so sure about those. If they stop right at 2.4 gHz, how am I going to pick up 2.412 gHz (wifi channel 1) or 2.437 (channel 6)?

These new boards really got me interested..
They don't look like any microwave band freq counter that I've ever seen..
I wonder if they are really counters, and if they would work above 2.4 gHz??
They don't cost much.. I might have to find out if they do anything.. Since they look like just the display board, and not the whole counter..

Richard Lee

Today I was looking at another counter.. The Surecom SF-401 Plus
It cost more, about 45USDs, but it has a very nice display. Not only has Bars,
but a numerical reading of signal strength as well.(small 3 digit number under the F in Freq).
It has a wider freq range and a nice BNC on top. It does some subtone decoding too.
I can use that subtone decoding for Ham stuff or other comms needs.

I may order this one from Amazon, since I'm not sure my diode detector will work very well
at such a high freq. 2.4 gHz is up there, and my diode is driven by a small LNA..
That LNA is not going to have much gain at 2.4 gHz..
So, instead of changing out the LNA, maybe I should buy a new toy!


Richard Lee

It seems like a much better tool.. Looks cooler too. And, it's only 7 or 8 USDs more..
I wasted that much at the Bowling lanes today. And I don't know how to bowl.
Besides, anyone who has a Valet, should be able to afford 45 bucks.. (and my valet gets lighter.:))

I just ordered some other stuff that I needed, so I'm going to wait a few days
before buying the SF-401 Plus. Let the smoke settle.

ab cd

Senior Member
Oops... this stupid spelling checker of my phone... I might have typed walet insted of wallet, and this stupid spelling checker silently "corrected" it by replacing w by v (valet) insted of adding an l (wallet).

I wish I was rich enough to have a valet!
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Richard Lee

My new F-401 Plus will be here in a few days. Or maybe this weekend?.
I will check it out some and post a little report here.

I'll have to try it out with the 915 mHz Yagi antenna I've been wanting to test.
I install an adjustable pad (attenuator) inline with the counter, to keep it from getting blasted with too much RF..
Since this is a lower freq, I'll stick in my old 1.5 gHz counter to start with.. :)

I have no idea when the new Directional Coupler will get here from SHENZHEN!
Estimated delivery Saturday, Mar 12, 2016 - Wednesday, Mar 23, 2016

ab cd

Senior Member
I have no idea when the new Directional Coupler will get here from SHENZHEN!
Estimated delivery Saturday, Mar 12, 2016 - Wednesday, Mar 23, 2016
Only 1 to 3 weeks! You are lucky, better than most of my orders which took 1 to 2 months.

Looks they shipped your order by a Steam Ship. Most of my orders from China are shipped by a small Sail Boat, or sometimes even in a Canoe. :(


Most of my orders from China are shipped by a small Sail Boat, or sometimes even in a Canoe. :(
The current outright world record for a circumnavigation is held by a sailing boat. 15 days faster than a nuclear submarine. :D

Richard Lee

It ( Directional Coupler) came via Air. Currently in NYC.. Only 200 miles, or 2 or 3 days away from here..
I believe the new counter will be here tomorrow. :) (Amazon is fast sometimes).

I've been looking at wifi antenna designs. I'm thinking about a broad-beam directional or Sector wifi (2.4gHz). Also known as a Hot Spot antenna.?
It would be pointing south, and I want to have coverage both SE & SW. About 90 deg wide would okay, but wider be nice.

Something like this, but with vertical polarization.

I was thinking about using the 300 mm design I posted about once. (Scaling it down to 2.437).
That had good gain. Maybe the design could be used with a screen reflector.?.

Any ideas guys?

Richard Lee

That would be too directional. I need a wide beam (without a fry pan upside the head).. ;)

The counter works, but the signal generator might need a booster amp, because signals
are too weak to register any bars. And the numerical value is very low..
(Key up a UHF radio near it and it works great. Just like those in the videos).

The highest freq I could see was 3.4 gHz. (See insert in picture)
But maybe it would have gone a little higher with some RF power.
But, since it's only rated for 3.0 gHz, I was just looking for fun.
I have been told (by a vendor) it's only good down to 100 mHz, not 27 as listed.
I think I have an LNA that works up to 3 gHz, I'll check it out tomorrow.

It doesn't seem to be very sensitive at 2.4 gHz. :(
Even after installing a 2.4 antenna on it, it still could not see a 2.4 router just a few inches away..

Once I get the 800-2500 mHz coupler, I'll see it I can use an Amp to get a higher signal out of the the monitor port.
I would like to see about half the bars lit up with a high SWR, to make it easier for tuning things up..

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Richard Lee

The microwave directional coupler 800-2500 mhz came in this morning. It looks like a $100 unit that I got for $9USDs.. I'll test it this afternoon