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November 22, 2019 at 8:52 pm #310KR2QParticipant
I saw a similar question recently posted, about isolation of the antenna switch, but this is a bit different.
I am a serious HF contester. With 10m so horrible and spotty, I don’t want to miss any openings. I’m thinking of using an RSP1a to monitor the 10m band using a high gain triband (non trapped) yagi antenna about 55 feet (16m) up. It has 8 monoband elements on 10m (OB16-3). The antenna will almost always be pointed “south.” About 100 feet away, I have another yagi antenna (DB36 if that matters) at about 75′ up (23m) that I will use for transmitting on a different band (15, 20, 40, 80, 160). At times, I am sure that the DB36 will be pointing directly at the OB16-3.
I want to be sure that transmitting on a band that far away (both physical distance and frequency distance) will not “destroy” the SDRPlay view of the 10m spectrum….and hopefully not “blow up” the 1a itself due to overload.
Any knowledgeable comments will be greatly appreciated.
de Doug KR2QNovember 22, 2019 at 9:27 pm #311RogerParticipant
A couple of things to consider:
– The RSP1A is a wideband receiver
– The maximum continuous input level is 0 dBm (10 dBm intermittent)
– The maximum power input is at any frequency (not what RSP1A is tuned to)
You are probably running a linear and you will have a lot of gain on the DB36.
The continuous power input to the RSP1a will depend on the Tx power level, mode (USB, AM, RTTY, FT8 etc), the path loss over 100 feet and the off band response of the OB16-3.
It would take a lot of testing with different bands and modulation modes to determine if less than 0 dBm was present on the antenna output going to the RSP1A.
So you need to consider one of the following…
One is to get a MFJ-1708B SDR switch which isolates the RSP1a whenever you transmit.
The second is to use a Rx protector box to protect the RSP1a. You can build one or buy one of the commercial units from Array Solutions, DX Engineering or other vendors on the Internet.
November 22, 2019 at 10:24 pm #314KR2QParticipant
- This reply was modified 2 years, 7 months ago by .
Tnx so much for the info and suggestions. I want to be able to receive (see the spectrum on 10m) while transmitting, so the “switch” is not gud for my purposes.
I did find the RX Protector Box on DXE and that would work, for nearly the same price as the 1a (LOL).
The OB16-3 which I will use on 10m does have all 3 driven elements tied together, so it will be especially good at picking up my xmited signal on other bands. Thanks for reminding me that the 1a receives everything, not just the band I’m tuned to. Maybe a BP filter for 10m for the input to the 1a would work…or help.
I do not run an amp. In fact, I have been a QRP operator for the CQWWDX contest for many years, so the most I squirt out from the rig is 5 watts. And then I have loss in the feedline (nearly 200 feet), etc. I’ll put my 2nd K3 on the OB16-3 and see how strong I am when transmitting with my 1st K3 on DB36. Probably pretty strong, even at just 5 watts. <grin>
Thanks for the input and ideas!
de Doug KR2Q
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