Loop Antenna Amplifier +


leslie norton
 

Hi Chris

Can i order the Loop Antenna Amplifier + yet? ie: have you stock yet?

Also just to confirm what i need to order.
I have a loop already im going to use, loop leads terminate in a BNC (its plugged into my ALA-100 at the moment) the other end is terminated in a BNC that i plug into my SDRplay Dx with adapter to fit into correct port that supplies the voltage instead of a BiasT.

Thats the way i intend to run the Loop Antenna Amplifier +

So if im right all i need to order (UK) is the Loop Antenna Amplifier + at £35 without the base unit.
Thanks
Les


Hisao Uose
 

Hi Les,

My "Antenna Amplifier +" has been delivered (to Tokyo) this week and I replaced the VLF/HF amplifier which I used for a few months with the new unit. It is working fine and it has higher frequency range to VHF as intended (roughly +20dB higher gain over 100MHz). I'm using 12V power supply with a Bias-T to feed the amplifier but the unit worked fine with 5V supply when I tested as well, so the configuration you described should work fine I believe.

Regards,

Hisao


leslie norton
 

Thanks Hisao
Didn’t want to order if they weren’t in stock as i know Chris is only just getting back after the lockdown.

Great how yours worked, pointless me buying the Base unit if i don’t need it, I know the BiasT is good on the SDRplay as ive used it with my MLA-30 and my Wellbrook MLA-30 but just wasn’t sure about the  Loop Antenna Amplifier + as the Its called Base unit on the order page rather than BiasT so i was a little confused what it actually was.

Cheers
Les G4JNW

On 5 Jun 2020, at 09:07, Hisao Uose <hisao.uose@...> wrote:

Hi Les,

My "Antenna Amplifier +" has been delivered (to Tokyo) this week and I replaced the VLF/HF amplifier which I used for a few months with the new unit. It is working fine and it has higher frequency range to VHF as intended (roughly +20dB higher gain over 100MHz). I'm using 12V power supply with a Bias-T to feed the amplifier but the unit worked fine with 5V supply when I tested as well, so the configuration you described should work fine I believe.

Regards,

Hisao


Chris Moulding
 

Les,

We have the Loop Antenna Amplifier + back in stock today ready to ship.

As Hisao says the head unit will work as you suggest with the SDRPlay receiver.

The Bias T is  a unit that supplies DC voltage up the antenna feeder to the head unit. It uses a 2.1 mm DC socket to connect to a 5 to 15 V power supply.

The base unit has a USB B socket to supply 5V to the head unit. It also has an additional amplifier to provide extra gain for insensitive receivers.

Regards,

Chris


leslie norton
 

Thanks Chris I’ll get it ordered then, might as well get the full lot, just in case i use the SDRplay on another port thats not supplying the BiasT voltage.

Les

On 5 Jun 2020, at 09:54, Chris Moulding <chrism@...> wrote:

Les,

We have the Loop Antenna Amplifier + back in stock today ready to ship.

As Hisao says the head unit will work as you suggest with the SDRPlay receiver.

The Bias T is  a unit that supplies DC voltage up the antenna feeder to the head unit. It uses a 2.1 mm DC socket to connect to a 5 to 15 V power supply.

The base unit has a USB B socket to supply 5V to the head unit. It also has an additional amplifier to provide extra gain for insensitive receivers.

Regards,

Chris


leslie norton
 

Have ordered:
Note for some reason Paypal does not send my full name unless i do it through ebay, strange!
You’ll get my full address and name as Leslie, rather than Les Norton, please address using Les Norton as the couriers and royal mail guys know me by Les Norton.
Nothing stranger than paypal sometimes haha
Cheers
Les
G4JNW

On 5 Jun 2020, at 09:54, Chris Moulding <chrism@...> wrote:

Les,

We have the Loop Antenna Amplifier + back in stock today ready to ship.

As Hisao says the head unit will work as you suggest with the SDRPlay receiver.

The Bias T is  a unit that supplies DC voltage up the antenna feeder to the head unit. It uses a 2.1 mm DC socket to connect to a 5 to 15 V power supply.

The base unit has a USB B socket to supply 5V to the head unit. It also has an additional amplifier to provide extra gain for insensitive receivers.

Regards,

Chris


Hisao Uose
 

Hi Chris and Les,

I've just installed the new unit yesterday and am testing it since in various conditions (during the self-isolation). The loop element is the same 1m diameter copper tube I used with the VLF/HF unit.
During the testing I found interesting results related to the power supply voltage.

(1) my environment
* There are a number of powerful AM broadcast stations in my area (Tokyo). Among them the AFN Tokyo (American Forces Network) is prominent because of its highly compressed modulation on top of the high output power. The frequency of AFN is 810khz.
* My house is about 500m away from a motorway and the motorway has its traffic information service facilities using leaky coaxial cables at 1620khz. Although this traffic information signal at 1620kHz is aimed for cars traveling on the motorway I can listen to the faint signal at my house if antennas and receivers are not overloaded.

(2) performance check using those signals (810kHz and 1620kHz)
* Of course the overloading at active antennas and/or receivers easily produces higher harmonics in this environment. Because I have those two signals handy I always check if I can listen to the traffic information (not the second harmonics of AFN) as soon as I change the receiving configuration.

(3) effects of supply voltage to the head unit ("Antenna Amplifier +")
* I compared the reception of 1620kHz of the new "+" head unit using 5V (4.8V to be precise) and 12V (this is not the precise value. it's an unregulated transformer adapter and produces 14.8V when no load) power supplies. The followings are the screen shots of the experiment (first image: 5V and second image: 12V).


5V


12V

* As you can see, while the new head unit cannot cope with the strong 810kHz signal with 5V supply voltage producing the second harmonics, it could handle the signal nicely with 12V supply. You would notice that there are other spurious signals in the 5V result when you compare the two.
* I don't think I have the same problem with the VLF/HF unit with 5V power supply. Maybe it's because the new unit has more gain than the old VLF/HF unit but I'm not sure.

(4) provisional conclusion
* I need to do more rigorous performance tests to draw any conclusion but it seems that using higher operating voltage can avoid overloading in some severe conditions.

Cheers!

Hisao


leslie norton
 

Interesting, wonder where you supply the 5v from, does the airspy supply it (sorry i know nothing about the airspy) or are you providing 5v from a power supply?
I have ordered the kit inc the base unit (thought it worth while in the end, in case i don’t always use it with the SDRplay)

Do you see any difference in the VHF bands in voltage too?
Or the higher HF bands?

On 6 Jun 2020, at 05:58, Hisao Uose <hisao.uose@...> wrote:

Hi Chris and Les,

I've just installed the new unit yesterday and am testing it since in various conditions (during the self-isolation). The loop element is the same 1m diameter copper tube I used with the VLF/HF unit.
During the testing I found interesting results related to the power supply voltage.

(1) my environment
* There are a number of powerful AM broadcast stations in my area (Tokyo). Among them the AFN Tokyo (American Forces Network) is prominent because of its highly compressed modulation on top of the high output power. The frequency of AFN is 810khz.
* My house is about 500m away from a motorway and the motorway has its traffic information service facilities using leaky coaxial cables at 1620khz. Although this traffic information signal at 1620kHz is aimed for cars traveling on the motorway I can listen to the faint signal at my house if antennas and receivers are not overloaded.

(2) performance check using those signals (810kHz and 1620kHz)
* Of course the overloading at active antennas and/or receivers easily produces higher harmonics in this environment. Because I have those two signals handy I always check if I can listen to the traffic information (not the second harmonics of AFN) as soon as I change the receiving configuration.

(3) effects of supply voltage to the head unit ("Antenna Amplifier +")
* I compared the reception of 1620kHz of the new "+" head unit using 5V (4.8V to be precise) and 12V (this is not the precise value. it's an unregulated transformer adapter and produces 14.8V when no load) power supplies. The followings are the screen shots of the experiment (first image: 5V and second image: 12V).

<dummyfile.0.part>
5V

<dummyfile.1.part>
12V

* As you can see, while the new head unit cannot cope with the strong 810kHz signal with 5V supply voltage producing the second harmonics, it could handle the signal nicely with 12V supply. You would notice that there are other spurious signals in the 5V result when you compare the two.
* I don't think I have the same problem with the VLF/HF unit with 5V power supply. Maybe it's because the new unit has more gain than the old VLF/HF unit but I'm not sure.

(4) provisional conclusion
* I need to do more rigorous performance tests to draw any conclusion but it seems that using higher operating voltage can avoid overloading in some severe conditions.

Cheers!

Hisao



Hisao Uose
 

Hi Les,

I'm using a Bias-T board (around 5GBP) bought from eBay with regular AC/DC power adapters to power the head unit. I'm not sure if you can apply higher than 5V using the CCW base unit. My original set (VLF/HF unit with base unit) was rated at 5V but I accidentally applied 12V to the combination and blew the transistor inside the base unit (head unit remained intact). So please make sure that the allowable voltage before you do any experiment! Of course you should be able to use CCW's Bias-T to feed "+" unit higher voltages up to 15V.

I did see differences in the VHF band when I change the operating voltage. It seems that applying higher voltage gives higher gain (about a few dB?). Higher gain itself is very nice but in my environment (where FM stations are powerful as well), high gain causes a problem in FM band. I see many spurious signals in the band even when I use it with 5V (although better than using it with 12V). I don't know the overloading occurs at the head unit or receiver side yet. I'm going to do a test when I get attenuators to lower the antenna output signals. Because the airband is perfect without any spurious for both operating voltages it could be the overloading at the receiver side (HF+ Discovery seems to have separate pre-selector filter banks for FM and airband, if I understand the specification correctly).

Cheers,

Hisao


Chris Moulding
 

Thanks for posting your results with different supply voltages.

It's worth noting that you are giving it a severe test as the signal levels in the medium wave broadcast band are extremely high in Tokyo. Looking at the display the strongest signal is 70 dB above the noise floor.

The amplifier is designed so that it doesn't exceed the maximum supply current from the internal 4.7 V bias-tee in the SDRPlay receivers. This does limit the IP3 and IP2 performance when fed with lower voltages but the noise figure of the amplifier is at it's best (lowest) value.

If the amplifier is fed with 12 V then it draws more current and the IP3 and IP2 figures are at the optimum value but the noise figure is slightly higher.

It's a typical RF engineering compromise. You cannot have lowest noise figure and highest IP3/IP2 together!

Regards,

Chris


Chris Moulding
 

From what you describe at VHF, Hisao, it looks like it's overload of the receiver.

Using the higher supply voltage improves the amplifier IP2 and IP3 performance as you proved on the medium wave test so it probably testing the limits of your VHF receiver.

Regards,

Chris


Hisao Uose
 

Hi Chris,

That was my guess too. I'll do a test with attenuators with various vales.

Thanks!

Hisao


leslie norton
 

Good point then, pleased i ordered the base unit too then.
I do intend to do some tests on both voltages and see whats best. I favour the BiasT in the SDRplay but my FTDX3000 has the capability to use an Rx only antenna in port 3 in fact i have in some cases used 3/1 which allows be to Rx on the Rx port and Tx on port 1 which is my end fed long wire.
VHF would of course be SDrplay only and good to compare a loop and vertical.

Les

On 6 Jun 2020, at 09:32, Hisao Uose <hisao.uose@...> wrote:

Hi Chris,

That was my guess too. I'll do a test with attenuators with various vales.

Thanks!

Hisao


Hisao Uose
 

Hi Chris,

I remember that you suggested me to use a smaller loop (for example 0.5m) before and I think I would try that to solve the overload problem. My current element is 1m (made with 9.52mm copper tube) and might have excessive gain. Do you have any insight about the roll off frequency at the higher end when I use the same copper tube with 9.52mm diameter (the thickness is 0.8mm)? Or recommendations for using other materials or size..

Thanks!

Hisao


Hisao Uose
 

Hello again!

Today I've made a handmade attenuator (with 21dB loss) and done some tests in FM band. On the contrary to my (and Chris's) guess, the spurious didn't go even with the attenuated signal was fed to the receiver (even I've inserted the 4-way splitter making the total attenuation over 27dB). The shape of spectra obtained with the attenuator inserted are almost identical (with the lower signal strength of course) to the ones without the attenuator.

So I swapped the antenna unit with the VLH/HF unit again (with 5V power supply). With the VLF/HF antenna unit the spurious images in FM band have gone but with lower signal levels (this unit is not designed for this frequency range for the first place). Still the signal strength in FM band is enough for my place so I'll use the VLF/HF unit with 1m loop for a while.

Probably the electric field in FM band here is excessive to the HF/VHF units including "+" especially because I use a relatively large aperture loop element (1m diameter). Following Chris's suggestion I'll make a smaller loop to be paired with the "+" and do more experiment.

One more thing, the second harmonics of AFN (810kHz) is inaudible with the VLF/HF unit (with 5V). With "+" unit a faint interference was audible even when it's powered by 12V. That is very impressive.

Cheers!

Hisao


Hisao Uose
 

Is it possible that this level of VHF signal can saturate the Ferrite inductance in the Bias-T circuit?? I've just noticed that my Bias-T circuit is rated to 100MHz.


Chris Moulding
 
Edited

The signal levels on the FM band in Tokyo must be very high.

The VLF/HF unit had two low pass filters built into the head amplifier. One used capacitors across the common mode choke which filtered the output and the first used an 82 pF capacitor across the input to improve the match of the loop at HF and provide a low pass filter across the input.

The overall loss at 100 MHz with the VLF/HF amplifier was around 25 dB.

The latest "+" version is designed so that the low pass filtering rolls off at 150 MHz.

To avoid overloading it on the FM band with such high level signals try a smaller loop say 0.5m.

It's unlikely that the signal levels on the amplifier output would saturate the ferrite choke in your eBay Bias-T. The upper limit of 100 MHz will be caused by the self-capacitance across the choke winding affecting the 50 ohm match.

Regards,

Chris


Hisao Uose
 

Hi Chris,

I appreciate your advice. The VLF/HF unit is working very well indeed even in Tokyo. Especially after the upgrade replacing the common mode choke connecting the antenna element and the amplifier input with a transformer you provided, I no longer need an isolation transformer to suppress the common mode noise flowing to the receiver.

I'll work on the new "+" unit with a new loop as well. Do you think 0.3 m diameter is too small? It should reduce the gain about 10dB compared to the current 1m loop.

Thanks!

Hisao


Hisao Uose
 

Hi Chris,

I might have found the source of the interference on the VHF band when using the "+" unit in my location. It turned out that there are strong signals between 154.6MHz and 156.0MHz. This bandwidth is packed with multiple modulated carriers closely located each other. I don't know whether they are digital communications or some sort of beacon / radar. Because they almost fill the 1.4MHz bandwidth the total power should be very high.






In your message to Les (in another thread) you mentioned that "the common mode choke low pass filter capacitors in the head unit" determine the roll off frequency and it sounded (for me) that I could increase the capacitance to lower the roll off to around 120MHz (or lower frequencies which can reject those signals in 155MHz band). It would be great if you could give any suggestion on this modification (whether it's recommended or not, in the case I can do the modification, appropriate capacitance values and their locations).

Before I noticed the existence of those 155MHz interference signals, I tried two smaller loops (0.4m and 0.6m diameter). Both worked quite well with relatively small gain losses. However, the intermodulation didn't go away completely even when I use 0.4m loop (though, the interference in 0.4m loop is smaller than 0.6m loop). I'm hoping to use the "+" unit with the modification making lowering roll off frequency with 0.6m or 1m loop.





I appreciate your kind suggestions.

Best regards,

Hisao


leslie norton
 

Its always a balance between rejection and signal cut off Hisao
I just get no signals at all, i don’t need any rejection as i have no strong signals to overload.
I know Chris was going to do some tests.

On 13 Jun 2020, at 05:44, Hisao Uose <hisao.uose@...> wrote:

Hi Chris,

I might have found the source of the interference on the VHF band when using the "+" unit in my location. It turned out that there are strong signals between 154.6MHz and 156.0MHz. This bandwidth is packed with multiple modulated carriers closely located each other. I don't know whether they are digital communications or some sort of beacon / radar. Because they almost fill the 1.4MHz bandwidth the total power should be very high.

<dummyfile.0.part>


<dummyfile.1.part>

In your message to Les (in another thread) you mentioned that "the common mode choke low pass filter capacitors in the head unit" determine the roll off frequency and it sounded (for me) that I could increase the capacitance to lower the roll off to around 120MHz (or lower frequencies which can reject those signals in 155MHz band). It would be great if you could give any suggestion on this modification (whether it's recommended or not, in the case I can do the modification, appropriate capacitance values and their locations).

Before I noticed the existence of those 155MHz interference signals, I tried two smaller loops (0.4m and 0.6m diameter). Both worked quite well with relatively small gain losses. However, the intermodulation didn't go away completely even when I use 0.4m loop (though, the interference in 0.4m loop is smaller than 0.6m loop). I'm hoping to use the "+" unit with the modification making lowering roll off frequency with 0.6m or 1m loop.

<dummyfile.2.part>

<dummyfile.3.part>

I appreciate your kind suggestions.

Best regards,

Hisao