The Hi-Z connection

Useful information regarding antennas for SDR products.
Paul
Posts: 261
Joined: Fri Feb 17, 2017 9:52 am

The Hi-Z connection

Postby Paul » Sat Jul 28, 2018 7:13 am

I have an RSP2, with a long-wire antenna, an H/V/UHF discone, an active mini-whip and an ALA-1530LN (plus a cobbled-together hula-loop and a “legacy” Rfsystems EMF antenna, played with now and again).
An “upstream” mechanical selector allows for a fair bit of flexibility.
I do have a problem concerning use of the High-Z port that I have so far been unable to resolve.
The long-wire works just fine on this connection, whether directly connected, pig-tailed via a simple length of RG58 coax/SO239-PL259, or pig-tailed with a Nooelec mini balun.
However, the ALA-1530 and active mini-whip, which both work well on the 50 ohm Port A connection work very badly indeed on the Hi-Z input connected via any of the foregoing options.
To be honest, I have not tried the “direct” connection, leaving that as a last-ditch option, as it would restrict flexibility.
I have read Andy's (g1hbe) obviously knowledgeable advice to another subscriber on the forum, that is quite clear and very obviously works for the ALA-1530 and have followed the diagrams offered by SDRPlay to no avail so far.
What absolutely confounds me, is why both of the active antennae behave in ian dentical (highly disappointing) manner, with extremely degraded reception over that when connected to either of the 50 ohm ports, whilst the long-wire performs well (within it's specification).
I am wide open to any suggestions to try and resolve this anomaly.

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g1hbe
Posts: 367
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: The Hi-Z connection

Postby g1hbe » Sat Jul 28, 2018 7:30 am

Hi Paul, it's Andy again. I bet you think I'm stalking you!

I honestly cannot think of any reason why you should be seeing such poor reception on the Hi-z input from your active antennas, unless you are making a mistake with the connections. The output from the antennas DC power injector box should go to the Hi-z input directly or via a suitable balun.
Is the balun OK - I presume so as it seem to work with your wire antenna,
Try a direct connection, jut to prove a point. Remove the balun. Link N to G and connect the braid of the coax there. Connect the inner of the coax to P. This isn't ideal but I used it for months and got good performance.
BTW, what do you mean by 'bad performance' - weak signals or high noise level or lots of intermod?
Must go, there is water falling from the sky. I think they used to call it rain!

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Andy

Paul
Posts: 261
Joined: Fri Feb 17, 2017 9:52 am

Re: The Hi-Z connection

Postby Paul » Sat Jul 28, 2018 7:49 am

Hi Andy
If that's "stalking," please carry on.
I (hope that) I'm learning all the time and will, of course, try the direct connection as you suggest and just for the record, the indoor hula-loop works just fine (within it's capability) on the Hi-Z also, via pig-tail with balun and seems surprisingly good.
As for the bad performance of the active antennae, I'll try to quantify it more specificlly when time permits.
BTW it's not raining down here not just yet, but gusting up a bit!
Thanks for sharing your knowledge and time too.

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Mike2459
Posts: 125
Joined: Mon Jul 24, 2017 8:24 pm

Re: The Hi-Z connection

Postby Mike2459 » Sat Jul 28, 2018 5:55 pm

Re: Paul wrote: "As for the bad performance of the active antennae

Paul, Is there a possibility that your power supply for the active antennas is overloaded, shorted or open circuited when the active antennas are connected to Hi-Z?

A way to check this is to power down the 12 volt DC antenna supply while listening to a weak signal. There should be a noticeable drop in signal strength.

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Paul
Posts: 261
Joined: Fri Feb 17, 2017 9:52 am

Re: The Hi-Z connection

Postby Paul » Sat Jul 28, 2018 6:33 pm

Thank youM Mike, both work well on the 50 ohm ports and I finally got around to making a direct connection between the Wellbrook and the Hi-Z input as suggested by Andy.
Coax inner to P, braid to N with a link to Gnd
I should, I know have done it before,however, it was pretty reasonable on Port A, butI was looking for ny possible improvement.
This indeed worked and I achieved clear and reasonable signals, but at what appeared to be a quite limited frequency range.
I have reverted to using the 50 ohm Port A for both the ALA-1530 and active mini-whip as the performance on this is actually better.
Connections and power supplies checked and rechecked with one faulty bnc connector replaced, but otherwise all is tickety-boo.

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Mike2459
Posts: 125
Joined: Mon Jul 24, 2017 8:24 pm

Re: The Hi-Z connection

Postby Mike2459 » Sat Jul 28, 2018 8:31 pm

That's good to hear. As to HF reception there have been zero sunspots for 30 of the last 31 days.

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Paul
Posts: 261
Joined: Fri Feb 17, 2017 9:52 am

Re: The Hi-Z connection

Postby Paul » Sun Jul 29, 2018 6:17 am

To be honest, I must have got something wrong since I seem to be alone on this; the technology involved is proven and used by those whom I respect.
Since it works fine with a simple long-wire and home-made Hula-loop, with any connection used, there is patently obviously zero wrong with my RSP.
I can undersstand that the ferrite mix in the mini-balun (in one connection option) may be unsuitable for either active antenna, but do not undersand the better than before, but restricted performance when connected by the direct, simplest method.
I do have some clip-on ferrites on the inputs/outputs and perhaps it may be worth experimenting with removing them.
As an observation only, on the 50 ohm outputs, the active mini-whip (I recognise that they don't seem to rate much favourable comment) performs very well down to 60 KHZ and lower, whereas on the same inputs, the Wellbrook, whilst noticeably better in NDB land doesn't receive the 60KHZ time-signal nearly as well (although at 198 Mhz it's far better, also true on the HI-Z input, but in the NDB range is degraded to approxiately the same level as the mini-whip).
I will persevere with "fiddling" as circumstances permit.

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