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Longwire antenna question

Posted: Sat Jun 17, 2017 7:01 pm
by mschacter
I use RSP for receiving only. I have a longwire antenna approximately 75 ft. long. I have connected the wire directly to the P terminal of the Hi-Z port and grounded it as suggested by splitting the ground wire between the GND and N terminals. When I do this I only receive spurious signals in the HF spectrum - i.e. distorted signals from local broadcasters. Can't tell if they are MW, FM, television audio or some combination of all three. Why is this happening?

Do not have the same problem when I end-feed my antenna through a 9:1 transformer and connect it to the Hi-Z port via a short length (about 6 ft.) of coax. But in this scenario I find the performance disappointing - signals not much better than what I would get on a whip antenna.

Need advice please! Thanks very much.

Re: Longwire antenna question

Posted: Sat Jun 17, 2017 11:59 pm
by g1hbe
Are you selecting the Hi-z input? You have to click on the Hi-z button. Other than that I can't think of much. The RSP is very sensitive on all bands.

Re: Longwire antenna question

Posted: Sun Jun 18, 2017 2:31 pm
by Paul
Hi there
For the past few days, it would appear that there is an issue with very poor HF signal propagation conditions, at least in my part of the world and if I were just making my initial antenna connections, I would not be in a rush to change them until you have had an opportunity to check on this possible propagation issue.
I have no reason to suspect equipment malfunction as it has been changeable - so don't be disheartened.
For your information, I use a 20M long-wire, active RA0SMS mini-whip (successfully) and an H/V/UIHF discone, each of which behave differently, being better or worse than each other on occasion, depending on conditions.
Then long-wire is connected to the HI-Z port as per this link (without a balun): ... uidev2.pdf (First picture).
The min-whip to port A and the discone to port B (just in case I might ever use the bias T facility - although I can't see any advantage over using the SDRplay's built-in lna.

Re: Longwire antenna question

Posted: Sun Jun 18, 2017 2:38 pm
by Paul
Sorry - further to my last; the following may be helpful to you:

Re: Longwire antenna question

Posted: Thu Jun 22, 2017 3:46 pm
by ultravista
Paul - I too have the ra0sms antenna. It is producing noise everywhere in the HF region, so much so that it is entirely unusable.

The mast is ~ 25 feet, the bottom 15 feet is metal and the top is PVC. The mast is portable and rests on concrete - there is no real ground.

The ra0sms is mounted @ the top of the PVC. The coax runs loosely down the mast into the house. The power feed unit is 9v 500maH. The ground is connected back out to the mast via small gauge wire.

It is a noise producing machine. Compared to a 25ft wire thrown over my neighbors tree, the ra0sms fails completely. It is terrible.

How did you get yours working?

Re: Longwire antenna question

Posted: Thu Jun 22, 2017 9:20 pm
by Paul
I am in a rural location.
The RA0SMS is set atop a metal base plate ( ... 7QodUZcHPg,) which provides something of a ground plane, mounted at the top of an aluminium pole, at a height of no more than 8M above ground level and quite near to the house wall (doesn't have an especially favourable situation really.
I have about 1M of copper pipe as a ground, hammered into the stony earth as deeply as possible.
The antenna cable is RG58 and plugs are SO239/PL259's
The power supply to the accompanying transformer is from a stabilized 12V/1200ma adapter.
Generally the 20M longwire is better at higher frequencies and the min-whip somewhat better at the lower end.
Very occasionally, depending on conditions, the mini-whip can outperform the long-wire at the higher frequencies.
I never expected it to be better than the long-wire, but it really isn't at all bad and I believe could be made to perform better should I improve it's location and ground.
The RSP, transformer and all other "bits" share a common in-house earth to a cold-water copper rising main supply.
Good luck!

Re: Longwire antenna question

Posted: Sat Jun 24, 2017 3:14 pm
by ultravista
Paul - what are you using as a power supply for the ra0sms?

Around the house, I have many power supplies that are labeled as 12-15V and 100-150ma but when measured, are nowhere near the printed output. All are over voltage and current. Not one was true to the label. Not one was under voltage or current.

For example, one that is labeled 9V 500ma - it measures 13v 2.5a, it is 2000ma higher than the label ...

An Archer Universal Adapter that goes from 3-12V in 6 steps is actually 3 (5.2V), 4.5 (6.9V), 6 (8.8V), 7.5 (10.6V), 9 (12.6V) and 12 (16V).

With that said, where can I find a true 12V 100mA power supply for teh ra0sms?

Re: Longwire antenna question

Posted: Sat Jun 24, 2017 5:57 pm
by Paul
Probably not very helpful to you.
I am UK base, but the psu was bought in Germany some time ago.
It is a MW911GS IC1200 STABLE 3/6/9/12V 1200MA - never measured it's output, but has worked satisfactorily.
It is on the 12V setting and I am in no way tempted to try a lower voltage setting as it may cause it to malfunction/overheat.
I would suggest consulting a reliable electrical supplier.
For your information - continuing quite frequent bad propagation here at the moment - comes and goes, but could I suggest trying your RA0SMS (when you conquer your noise problems) on broadcasts in the L/MW bands for starters, where mine consitently somewhat outperforms the longwire.
Depending on conditions, it is sometimes better than either of my two other antennae - in fact, very occasionally quite spectacularly.
Right at his moment the signal on the mini-whip is better on 8825Mhz (Santa Maria), than that on the longwire, although the signal isn't that great here anyway.
I do not pretend to know the answer, unless it is a polarisation effect.
Best wishes