| KO4UHL |
Rating:    |
2022-06-14 | |
| Extra Protection Receiver Guard 5000HD, |
Time Owned: 0 to 3 months. |
| After working with an Icom 7300, with a PTRX board, this will be a new experience. I built an antenna switching unit for it, so I could use my SDR independently, with the 7300 shut off. I used a Tohtsu CX-800M Coaxial Relay with 12 VDC coil to do this and it worked very well. The PTRX protected my SDR from transmissions from the 7300. But because of hard times I had to sell my 7300. So now I have an IC 718 and just purchased the MFJ unit to use my new setup. Not much I can say on this other than if you want to protect your SDR 100%, you might want to get one of these fro Dx Engineering......Receiver Guard 5000HD, Receive Only Front End Protector. It has a clamping circuit that blocks any RF fro hitting your SDR. I will say more when I get it all hooked up. |
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| N4LQ |
Rating:   |
2022-03-05 | |
| Warning for SDR use |
Time Owned: more than 12 months. |
Update for the MFJ-1708B-SDR
Since both the older 1708 and SDR models are merged into one review I will update on the SDR version now.
I have one and wondered why my separate receiver seems weak then a friend sent me his 1708/SDR saying it would not work at all. Here's what I discovered.
Both our units had parts blown out in the receiver protection circuit. Per the schematic, the "transceiver" input actually goes directly to the SDR receiver so-239 jack! When the relays are triggered, the RF is rerouted to the antenna but this takes a few milliseconds to happen. Meanwhile your poor SDR gets the full 100watts. The protection circuit consist of 9 ohms or resistance and a pair of back to back diodes to ground. This were blown to smithereens. When this happens, all power goes to the SDR receiver....Insane. So why did the protection blow? Simply because the RF sense did not trigger. Why not? Well for one things, the manual incorrectly tells you to install the strap on J2 toward the left. This disables the RF sense therefore the protection diodes get roasted until you let up. This is a stupid design and I DO NOT RECOMMENT EVER USING THIS WITH an SDR radio!
Some folks have reverted to using the CTRL keying jack to key directly. Still there will be a huge initial surge of RF on the SDR rx until the relays throw.
Avoid this product. The old 1708b model works fine and the receiver is never connected to the transmitter but of course you can't listen to both receivers at once. That is the only "advantage" to the 1708 SDR version.
Please study the schematic because you could loose both the 1708 sdr and your SDR receiver with this thing. A receiver protector will help save the SDR rx but not the 1708 sdr. It's hopeless. Look for another solution. 73 N4LQ
I'm using this with a DX-60 and HQ-150. I use the aux jack to mute the speaker. The response and change over time is so fast that no one detects any contact bounce or dit shortening. You can adjust the delay time down to zero so it's like QSK if you aren't bothered by relay noise. I usually leave enough delay to hold it between cw letters.
Isolation seems very good between rx and tx.
excellent product. |
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| KB2YG |
Rating:   |
2022-01-06 | |
| Problems with the RF sense circuit |
Time Owned: 0 to 3 months. |
| Recently, I received an MFJ-1708B SDRS for a birthday present. I installed this antenna switch to the output of my Drake TR7, ran the SDR output to my RSP2 SDR receiver and used my 12V power supply to power the MFJ. The MFJ-1708B has an internal 2:1 splitter so both your transceiver and SDR receive equally. An RF sense circuit in the MFJ automatically opens the path to the SDR when it senses RF power from the transceiver. At first, the unit worked properly, allowing me to use the RSP2 SDR as a spectrum scope and my Drake as a receiver. Within 2 days of light use, I noticed my Drake TR7 receive sensitivity was poor but the SDR received properly. Some troubleshooting revealed the MFJ-1708B had D3 shorted and resistors R11 and R12 open resulting in a degraded receive signal to my transceiver. This appeared to be caused by transmit RF from the Drake overloaded the receive path the the SDR. For whatever reason, the sense circuit in the MFJ-1708B didn't act properly. The repair was easy. After replacing the 3 components, the MFJ works properly again. Thanks to MFJ for the D3 diode that protected the SDR from damage. I now use my Drake TR7 PTT line to key the MFJ-1708B at it's "CTRL" input. This assures the MFJ will switch with PTT from the transceiver and not the RF sense. I saw several other reviews stating their transceiver seemed to receive properly at first with the MFJ-1708 but later on, received poorly. I suspect they have the same problem. The MFJ-1708B seems to work properly when the "CTRL" input is used but may be finicky using the units RF sense. |
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| NG9D |
Rating:      |
2021-02-06 | |
| unsolicited review |
Time Owned: 0 to 3 months. |
The new switch is functioning well - using RF Sensing or Control Line - Video of ICOM IC-718 + SDRplay RSP1A Panadaptor on YouTube NG9D channel. Links to YouTube videos are removed from posts on eham, but it should be easy enough to find if you are interested. 73 Lynn/NG9D
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|
| TF3OM |
Rating:     |
2020-08-10 | |
| Very good, but more loss than expected. |
Time Owned: 3 to 6 months. |
In my remotely operated station (TS-480, remote RF unit at my summer cottage 100km away, control faceplate at my home, RemoteRig units, Internet) I am using the same EFHW-8010 antenna for the transceiver and KiwiSDR, switched by MFJ-1708B-SDRS. This works very well as a panoramic adapter using CATSYNC to synchronize the operation of the TRX and SDR.
After installing the MFJ-1708B-SDRS recently, I noted that the S-meter on the Kenwood showed a lower value than the KiwiSDR, but previously they more or less tracked. I can compensate for this by using the built-in preamplifier of the Kenwood.
This seems to be similar to what noted by AC6BW below. I don't know how many dB the loss is, but it could be the value stated by him.
The switch is very useful besides this loss, but as my remote rig is located in a quite location I would have preferred less loss.
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|
| HB9PJT |
Rating:      |
2020-05-27 | |
| Very Good! |
Time Owned: 3 to 6 months. |
I am very satisfied with my MFJ-1708B SDR. It works perfect. The isolation of the RX out is very high because it uses 4 relays. Also the RF VOX does work very good. ARRL/QST measured a SWR of 1.5 at 440 MHz.
73, Peter - HB9PJT |
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| W7OZM |
Rating:  |
2020-05-26 | |
| After repair still does't work |
Time Owned: 6 to 12 months. |
I purchased 2 of these at Dayton last year and have used them for a year. On HF SWR is very good but on 445 uhf it's 2.5 to 1 and second 1 is 3 to 1. I never checked SWR when I put them in line but I was having issues with my Motorola XPR 5550 and noticed 3 to 1. Sent to MFJ for repair and they returned but still the same. I used 2 different dummy loads and SWR meters both read the same. I called MFJ and they didn't have any answers for me.They should not advertise that there good to 450 if there not. Anyone using these on 440 should check SWR.
This is the B model |
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| AC6BW |
Rating:     |
2020-05-25 | |
| Works good, but loss is higher than advertised |
Time Owned: more than 12 months. |
5/24/20: This is an update to my original review, and I have dropped the rating to 4-stars.
I have observed that the signal loss through the antenna to xcvr path is much more than the advertised 3 dB. In my case, it is usually about 1.5 s-units (9 dB). I opened up the unit, and reflowed the solder on the hybrid power splitter, but the loss did not improve. This amount of loss may be a problem when trying to receive very weak stations.
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I'm using the MFJ-1708B-SDRS, which is the latest 4 relay, RF sensing version of the 1708-SDR.
I couldn't find it in stock anywhere, so I ordered directly from MFJ. They put the order om backorder. I started looking around, and found one unit in stock at HRO in Minneapolis. I pounced on that one, then cancelled the MFJ order, and got quick delivery from HRO.
QST recently reviewed this unit in the March 2019 issue of QST. I generally agree with that review, and that is what prompted me to buy it. The B version adds additional isolation to the SDR port during TX. It uses 4 relays, and 50 Ohm transmission lines, to achieve the better performance. They recommend using the manual TX control from your rig, instead of the RF sensing circuit, due to a noticeable power spike during the RX to TX transition. I decided to heed this advice, and I have the CTRL input connected to the TX GND output of my rig. To enable this, you do have to open the unit up, and move one of the jumpers, since the default setting is RF Sense. The construction looked good, and I didn't notice any apparent defects.
I am using this unit with a SDRplay RSP1A SDR, and my rig is a FT-450D. I run the SDRuno SW. It's fantastic to finally have a waterfall and spectrum view with the FT-450D! I now can monitor activity on other bands, as well as easily monitor pileup activity, band conditions, noise and RFI, etc.
I haven't had any RFI problem with the unit, considering it has a plastic case. My vertical dipole is literally on the other side of my wall, 15 ft up on a pushup mast, running 600W, and I haven't had any issues. Likewise, I have a hex beam on a 35 ft mast, about 20 ft away from my operating position, and still no problems. I do have a good station ground, with all equipment cases bonded together to an outside ground rod, so that probably helps. I also have good common mode choke filtering on all my coax runs, especially for the vertical dipole, to keep RF off the coax shields. If you are having RFI problems, then I definitely suggest checking all those possible sources.
I tried using the CAT connection feature on SDRuno, to allow me to connect my FT-450D, HRD logging SW, and SDRuno together. This requires OmniRig. This works pretty well, although I have to connect to my FT-450D as a Kenwood TS-480S, and this limits the available controls in my HRD rig control module. I operate a fair amount of FT8, and once I put WSJT-X into the mix, I noticed some instability. Not all of the apps would change frequency in tandem with the others. I operate with CAT disabled most of the time, now, and I'm fine with that.
All in all, I'm very happy with the MFJ-1708B-SDRS, and am thrilled to finally have a panadapter display! |
|
| K2PBO |
Rating:     |
2020-05-24 | |
| MFJ 1708B SDR - Some Insights |
Time Owned: 0 to 3 months. |
I have only used this for a few days now and it is working OK as expected on HF, but I am discovering some things that others may want to know. I'll add to this as I get smarter.
1 - Very Important - With 12 V power on, relay K4 (that controls the grounding on the Aux. connector) and all the other 3 relays activate and stay activated. All 4 relay coils are in parallel. Thus, if your station keeps 12V power on all the time, those relays will get warm. When you transmit, they deactivate. (I confirmed this by looking at DC power consumption measured in the March 2019 QST Review: 12 mA on transmit; 155 mA on receive.)
Beacuse of this I had to rewire my station 12V power system because I was concerned about those relays being on 24 x 7 X 365 shortening their lives. It also says that continuity readings (eg to check for keying line grounding to the linear) made at the Aux. jack with DC power off, have little meaning.
I was expecting this to act like a standard T/R switch (relays close on transmit) but this acts as an inverted one (realys open on transmit.) There may be a protection reason for this that I will have to study.
More when I get more experience.
I have to add another important point: In order for your SDR to be connected to the antenna, 12V power must be on the MFJ - 1708B! This is due to the inverted logic used in the switching scheme.
I hope that their next version does not do it this way.
Steve K2PBO |
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| W8HK |
Rating:      |
2019-12-08 | |
| Works great!! |
Time Owned: 6 to 12 months. |
| I am using the updated version (1708B) with an RTL dongle, HDSDR and my FT-450D. I have to say, I'm impressed. Relays make a nice "click" when engaged. I am using the supplied 110V power cord rather than the 12VDC cord...just easier in my shack. I haven't noticed any stray RF issues, other than transmitting on 80 meters; I can hear myself coming over my PC speakers a little. That is no fault of the switch...that happened before I used a SDR setup. There were only two downsides to this product; the price and the time it took to get it from MFJ...almost a month. |
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