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Author Topic: Seperation  (Read 370 times)

N8OXQ

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Seperation
« on: February 12, 2022, 03:24:00 PM »

I am thinking about getting another SDR play receiver (RSPdx). I had the RSP2Pro but fried the input. Sent it in and they said it was dead. I made the mistake of having the receive antenna within 10 foot of a 50 Watt 2 meter transmit antenna.
This time I will be using a dipole 250 foot long hung at about 8 foot. Directly parallel to it will be a fan Dipole inverted V with peak at 35 foot and slopping down to 8 foot on the ends. The entire antenna will be no closer than 20 foot from the receive antenna.
I will run a max of 100 watts on the fan dipole on 10-160M.  Is this enough separation to keep this one alive?
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N2DTS

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Re: Seperation
« Reply #1 on: February 12, 2022, 05:13:49 PM »

Why not just protect the sdr?
I think the airspy hf plus discovery is a better receiver, but in any case, I would make a relay setup to short the antenna input to ground during transmit, or at least make a back to back diode setup to protect the input.
1N4001 diodes each way across the antenna input should protect the sdr.
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K4JPN

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Re: Seperation
« Reply #2 on: February 12, 2022, 05:47:39 PM »

While I don't have to worry about separation, I sometimes use my K2 as a separate receiver, also as the tuner for a converter.   I built a simple cable to plug into the receiver antenna bnc, it uses a couple of back-to-back 1N4002 diodes from the center conductor to ground and a .05 microfarad 500V disc ceramic capacitor in series with the center conductor.   It provides protection and saves going back behind the K2 to connect to the receiver input.
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K6YE

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Re: Seperation
« Reply #3 on: February 12, 2022, 08:49:18 PM »

It has been recommended to use an SDR TR-switch (like the MFJ-1708 SDR, either SO-239 or SMA) AND connect the transceiver control line to the SDR control line. Now you will never fry anything.

Semper Fi,

Tommy - K6YE
DX IS and CW RULES
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G4AON

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Re: Seperation
« Reply #4 on: February 13, 2022, 01:16:57 AM »

In my setup I have a HF active antenna feeding a distribution amp that in turn feeds an RSPDX, QS1R, the sub receiver in my K4D and a home brew RX.

The DC feed to the active antenna is auto switched via my linear amp keying line, so whenever I transmit on HF the active antenna is powered off. In addition there are back to back diodes and a series bulb as further protection.

The active antenna is an easy and low cost weekend project. The distribution amplifier is also easy to make but has been submitted for publication in the GQRP magazine “Sprat”, so isn’t currently available on my web pages.

The active antenna and interface is described at:
https://www.qsl.net/g4aon/pa0rdt_aa/

73 Dave
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VK6HP

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Re: Seperation
« Reply #5 on: February 13, 2022, 05:35:34 AM »

By coincidence, I've just been identifying some antenna socket hash from the RSPdx when operating on 2200 m (136 kHz).  I was feeding the RSPdx via a splitter internal to my TS-890S and, while there is no direct pickup of hash by the transceiver, enabling the Kenwood's antenna (passive) splitting function results in digital system noise which is audible and visible on the bandscope.  I haven't looked for noise on other bands but, on the face of it, if you're splitting an antenna output between an RSPdx and other receivers, a distribution amplifier with decent isolation makes sense.  As an aside, if you're interested in the new extremely narrow bandwidth FST4 modes on the low bands you'll likely also need an external reference source since the RSPdx internal reference is not stable enough for the long-duration modes.

For the OP, and perhaps to use alongside some of the suggestions so far, you could also consider a cascaded receiver protection system incorporating something like the Array Solutions front-end protector (https://www.arraysolutions.com/as-rxfep), or a homebrew equivalent.  The saturable transformers work very well in practice.

73, Peter.
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VA3VF

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Re: Seperation
« Reply #6 on: February 13, 2022, 06:19:59 PM »

I have one of each of the following, and they both work great. The RX antenna is 3 feet from the TX antenna. Max power here is 100W pep.

http://www.crosscountrywireless.net/receiver_protection_unit.htm

https://www.dxengineering.com/parts/dxe-rg5000hd

As for the Mini-Whip, I have a Russian clone, and it was the "protection" before I purchase the units above. The Mini-Whip overloaded to the max, but never burned, and never passed any high level to the receivers. That being said, DO NOT DO THAT.
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N8OXQ

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Re: Seperation
« Reply #7 on: February 15, 2022, 02:33:07 PM »

Thanks everyone for the replies. I was using one of these https://kd2c.com/rf-limiter but noticed that a 5 bar signal would drop to a 2 bar signal when connected! That is the reason I disconnected it and relied upon me remembering to unhook the coax to the SDR when transmitting (but forgot). That along with other signals are received on a discone antenna 60 foot in the air.  I plan on running the discone plus the long wire using an antenna switch to select. I think I will go with the MFJ1708B  since I also do some UHF work. My rig is a Yaesu FT 991. Thanks again.
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