We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Using ATU with SDR or Portable Radios?  (Read 731 times)

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Using ATU with SDR or Portable Radios?
« on: January 31, 2023, 1004 UTC »
Is it possible to enhance the reception quality (to improve weak DX signals on LW MW SW) plugging in Antenna Tuning Unit or Antenna Matcher to SDRs or portable radios with antenna input socket such as XHDATA D-808?

At what impedance do typical SDRs and portable SW radios with telescopic antennas and external antenna input socket operate best?
« Last Edit: January 31, 2023, 1006 UTC by alpard »
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline Pigmeat

  • Marconi Class DXer
  • ********
  • Posts: 6283
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #1 on: January 31, 2023, 1627 UTC »
Most portable antenna sockets are 50 ohms just like their big brothers except they use RG-73 mini coax with mono headphone plug to fit into the portable's jack. Go to a reputable ham radio site, not some offshore crap site, and they'll be able to fix you up with a chunk of RG-73 coax with the right adapters on both ends. It shouldn't cost much.

Antenna tuners will work well with portables. SDR's, I'm not sure about, nor the XHDATA D-808. Check with the seller.

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #2 on: February 01, 2023, 1239 UTC »
That's great to know. Thanks for your information.  I was under impression  that portable radios external antennas sockets with 3.5mm earphone jacks had different impedance input value than 50 ohms.     But it is good if they are 50 ohms nominal.

I used to think that because RX antennas can have wide variety of impedance input for RX antennas and they still work OK.
And they work well with wide freq. coverage active antennas, which has impedance of ???? not sure actually.
What impedance value do active loops and miniwhips outputs have?
« Last Edit: February 01, 2023, 1859 UTC by alpard »
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1240
  • Tampa, FL USA
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #3 on: February 01, 2023, 2210 UTC »
Even most desktop-class receiver are not actually 50-ohms across the wide spectrum of LW-MW-HF. The rating is more like an approximation. Also some portables are all over the place, especially the ones feeding the whip antenna and external antenna jack into the same front-end, as such designs are usually tailored more to the high-impedance of the whip antenna. YMMV.

It is not really a big deal anyway as long as there is enough signal-to-noise (SNR) present for audio recovery, and most decent radios have plenty of gain in both in the RF and AF sections to work with even relatively weak signals.... again assuming the signal is appreciably above the receiver's noise floor. ;)

At the extreme, an incredibly huge complex impedance mismatch can cause issues if the mismatch drops the available signal below a receiver's internal noise floor.

For example I have used a basic L-match tuner between a portable and a YouLoop antenna, as the antenna is way into negative gain (meaning loss) and presents a huge impedance mismatch (meaning more loss) with the particular portable. The loss is enough that many signals fall below the portable's own noise floor. The tuner brought the match close enough to moderately improve signal transfer. A small preamp would have done the same, but that meant another device to power.

On a related note, a tuner also can offer some passive preselection if there is front-end overload from say another band, thus a potential reason someone might use one with a receiver.  You can notice similar parts - caps, inductors, etc. - if looking at the schematics of an antenna tuner and a passive preselector. Basically the tuner is going to offer a (much) finer-grained matching ability.

BTW, I typically use 75-ohm RG-6 and RG-11 on most of my receivers. There is not enough mismatch to care. Then I use F-to-RCA adapters with RCA-to-1/8" male cables for connecting portables with 1/8" female antenna jacks to my outdoor antennas.



About the active antennas, the output of well-designed preamp ideally should be targeting a simple impedance around 50-75 ohms; give or take lots of percents. The reality is probably more like a few ohms to a few hundred ohms, as active antennas tend to have more than enough gain to overcome moderate mismatches.

There are even feedpoint preamps designed to match specific loads. For example the YCCC preamp design does not appreciably increase gain, but instead it is typically used to match a relatively short vertical antenna to a 75-ohms feedline at low HF and below, usually as a part of a multi-antenna vertical array controller needing well matched loads to electrically "steer" the array through phasing.
« Last Edit: February 01, 2023, 2311 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602
31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #4 on: February 02, 2023, 1300 UTC »
Great post. Thanks.

Yeah I thought RX antennas can be tolerated by receivers in some extent unlike TX antennas in impedance mismatch.
Currently I am using a couple of portable radios and cheap Chinese SDR with Active Miniwhip and longwire.

Active Miniwhip works well on 11 - 15 Mhz, but below that, it tends to overload the radios.
Longwire suffers from intermodulation problems especially at nights from MW stations on 3 - 5 Mhz.
I have a BCB filter for the longwire, and it seems work.  But sometimes when the intermodulation signals are very strong, it still comes through on some frequencies into the tropical band.

I was thinking of getting an ATU for dealing with this problems, but unsure it would be good idea, or get something like Active Loop antenna.  I recall using cheap Chinese MLA-30 Loop before, and it didn't overload any part of the bands.  It worked quite nicely on the whole spectrum from MW SW.  It didn't work on LW (no coverage).

The best antenna was the Wellbrook 1530 - worked from LW MW SW without any problems of overload or intermodulation, but it was quite expensive. I am not sure how they do it.
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1240
  • Tampa, FL USA
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #5 on: February 02, 2023, 1344 UTC »
Sounds like you have too much signal as it is. You might look into adding attenuation. IIRC, you are in the UK. Some examples starting under 10:

https://www.ebay.co.uk/sch/i.html?_nkw=Variable+Attenuator

CATV models often say down to 5MHz, but they usually work far below that, perhaps with a slightly higher mismatch and/or more or less attenuation. A "whatever" situation IMO.

I have various fixed dB "lab grade" SMA attenuators, but for a quick fix, I have a similar old Radio Shack 15-678 CATV 0-20dB variable model that comes in handy.
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602
31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #6 on: February 03, 2023, 2014 UTC »
Do you have to match the impedance of the input attenuator will accept and outputs, and the receiver's input impedance?
I see most of the old vintage attenuators input and output impedance is 600 ohms. Should they not be around 50 ohms to be able to be used with portables and SDRs?
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1240
  • Tampa, FL USA
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #7 on: February 03, 2023, 2239 UTC »
Since we are using standard coaxial feedline, you will want a typical inline coaxial attenuator rated for either 50 or 75 ohms. Most modern cable TV (CATV) uses 75-ohm connections, and a typically cheap 75-ohm CATV variable attenuator will work fine for our receiving purposes, as there is not enough mismatch to care even if using 50-ohm coax. You might need a couple of adapters for your coaxial connector type, but ones fine for receiving* are usually inexpensive on eBay or similar.

*You probably would not want to run a kilowatt transmitter through a cheap eBay connector. ;)
« Last Edit: February 03, 2023, 2243 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602
31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #8 on: February 05, 2023, 2317 UTC »
Yup sure. I was looking at the attenuators.  I might have something like that in the loft where all the old TV Satellite stuff are kept in the box. And also the old handset phones, PSUs are all piled into a few boxes.  But I was more attracted to the vintage heavy metal box attenuators for better build and more attenuation range.   

But the problem with those old sets are their input output impedance are usually 600 ohms.  They would be ideal for the old tube radios with wire fed antenna sockets and earth terminals - maybe they will work great together.

But with the modern portables and SDRs, I gather more of 50- 75 ohms ones are the ones which will work properly for attenuation.

Another point I have noticed was that my Active Miniwhip sometimes works great - when the 60m tropical band opened up, I could hear all the small powered DX stations from Brazil, USA and Cuba.  And the signals were too strong and they were over modulating my portable radio.  I pulled out the PSU feeding the active Miniwhip, and the miniwhip was working without amplification - as a passive antenna.  It has long coaxial cable up about 4 meter above ground, and very long earth wire, and it worked great quiet rxing the DX stations on 4 - 5 Mhz.

I might keep using this trick with my Active Miniwhip when the signals are over modulating.
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline Ray Lalleu

  • Marconi Class DXer
  • ********
  • Posts: 30417
  • Western part of France
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #9 on: February 06, 2023, 1201 UTC »
The antenna input impedances of small portable receivers are nothing like 50 or 75 ohms in the SW bands (and MW alike, if the socket can be used for MW). The inputs are high impedance input, so they can get signals from any short random wire. The result is good or fair for any frequency, except for some narrow bands in the SW range, exactly the reverse of what is sought after by hams looking only for their narrow bands in SW. Detox your brain from ham ideas !

To lower the MW overload when listening to SW, begin with a doublet antenna (horizontal dipole not sized for any specific band, with open/symetrical line). Such an antenna is good on SW and inefficient on MW (better in this way : look at the ideas from K6STI).

 
D/E/F/G/It/Sp : Dutch/English/French/German/Italian/Spanish
+/- : about 0.02 offset, ++/-- 0.03/0.04 offset
Balanced wire antennas, wire lines and ATU

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1240
  • Tampa, FL USA
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #10 on: February 06, 2023, 1622 UTC »
Agreed on the inputs, as noted earlier, portables tend to be high impedance. It is cheaper to just dump the attached whip and the external antenna jack into same frontend. Kind of like lots of portables skip on even basic $0.25 ESD protection diodes.

I have used symmetrical feedlines for various antenna projects, though just from a convenience standpoint alone, I suspect there are far more SWL enthusiasts here with dedicated MW/HF antennas running coax instead of twin-lead, ladder-line, or similar. ;)

Either way usually even a basic outdoor antenna has more than enough gain for a portable regardless of whatever feedline impedance characteristics barring a short, and even then that might work depending upon the frequency.

We know he has a seemingly working active antenna available, so that is a potential place to start before delving deeper into antenna design. Assuming it is not the active antenna preamp itself overloading, adding attenuation is the usual next basic step to deal with frontend overload.

Coax is present so I lean towards us starting with readily available and affordable attenuation options; be it a variable attenuator or stacking fixed attenuators if need be. Various F- and SMA-connector models are available for a few dollars at a variety of online vendors and electronics shops. Add a couple of cheap adapters if needed to insert the attenuator(s) between the bias tee and radio. Alternatively, three resistors can do the same if one does not mind a little soldering DIY job.

https://www.everythingrf.com/rf-calculators/attenuator-calculator

That said, this is not exactly ideal....

Quote from: alpard
miniwhip was working without amplification - as a passive antenna

....as Kirchhoff's current law applies. ;) So just like any other dipole antenna, even if your setup does not look like a traditional one, you could consider the radio circuitry (plus any electrical grounding, plus possibly the whip antenna, etc.) as one side of the antenna, and the coax running to your un-powered active whip as the other side of the antenna. Lots of YMMV there. It very well can and should receive signals, but I can imagine the resulting SNR is not great.
« Last Edit: February 06, 2023, 1631 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602
31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #11 on: February 07, 2023, 1152 UTC »
My Active Miniwhip works fine on say 6 - 15 Mhz with the preamp powered on.
But under 5 Mhz, it overloads the radio.  I have to switch off the preamp for 4 - 5 Mhz RXing with the Active Miniwhip.
So it depends on which frequency it is, the Active MiniWhip overloads or works great.

I also found that there is no one antenna which works well for the whole band or MW LW SW, unless it is active loop such as Wellbrook or MLA30.  And even these active loops, there will be portion of the band, where they are not good or medium performer.

I have 2x YouLoops, 1x Active MiniWhip and Random Wire, and they all work better for one part of the band better than the other bands.
I might go and DIY simple L-match tuner, because I have a few old variable capacitors lying around in the loft.  All I need would be a plastic pipe and enamel wire to wind coils to make inductor.
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #12 on: February 14, 2023, 1129 UTC »
Ended up ordering an ATU.
I try not to amass radio gears, but needs must.
Hopefully it will give extra front end and pass band filtering effects which will help curing the nasty intermodulation problems on 4-5 Mhz. 
But I am not sure on the result until tried and tested with the newly ordered ATU.
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline alpard

  • Full Member
  • ***
  • Posts: 245
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #13 on: February 19, 2023, 2030 UTC »
Tried the ATU with my portable radios and random wire.  It worked great.  Yes, ATU works well with the portable radios.
It peaks signals from the noise.  It seems helping curing the MW band signals overloads too. If one is using wire antenna and SW DXing, ATU is a must,  be it portable or tabletop radios.

Ended up getting a vintage Marconi Attenuator as well, but it is for 600 ohms.  It might help work better for longwire into the Hi-Z.
« Last Edit: February 19, 2023, 2034 UTC by alpard »
Tecsun S-8800, Lowe HF-225, XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip, Random Wire+ATU

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline Josh

  • DXing Phenomena
  • *******
  • Posts: 4303
    • View Profile
Re: Using ATU with SDR or Portable Radios?
« Reply #14 on: February 20, 2023, 1952 UTC »
Project IC-R71A recently made me deploy a GROVE TUN-3 Minituner for the first time in years. All I wanted to do was some quick ad hoc testing on the R71A, string a few feet of wire over a window frame and see how well the combo did.

The TUN-3 is a simple passive device, you have two controls, one sets the range and the other tunes. Have to say it wrung every drop of rf outta that 8ft piece of wire, amazing. Of course these work best below about say 15MHz but they can still help in keeping undesired rf out of the system, the lower the freq the better the q I suppose. I don't recall the Drake R8 I last used the TUN3 with as having so profound effect on me, but that was with a 70ft sloper from the second story down to the mailbox at the end of the driveway, much more rf to begin with in the R8/70ft sloper/TUN-3 setup than what one gets from 8ft of wire strung over a window sill feeding an R71A. The mail folks thought the sloper wire to the mailbox was for earthquake detection, heh.

Order a Grove TUN-3 MiniTuner today!
https://worldradiohistory.com/Archive-Monitoring-TImes/Grove-Catalog/Grove-1989-02.pdf
Also be sure to check out the new Fabulous Grove SR1000 Professional Surveillance Receiver! ! !

 I wholeheartedly recommend any suitable atu device for rx use when one wants to focus on a specific channel. And by suitable I mean one with manual controls. Most any new or used manual  HAM  transmatch will do, however don't expect the HAM models to tune below 1.8MHz, a lot of them only go down to 3.5MHz, so one made specifically for rx use would be best suited for lower freq excursions.

Or build your own;
https://aa7ee.wordpress.com/2021/03/23/a-passive-tunable-hf-preselector/
https://www.eevblog.com/forum/rf-microwave/lets-start-a-project-to-build-an-hf-preselector/
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qex/2003/03_04/page45/index.html
We do not encourage any radio operations contrary to regulations.

 

HFUnderground T-Shirt
HFUnderground Garden Flag
by MitchellTimeDesigns