External Radio "Transmit" doesn't drop off/switch back to receive

herbk@comcast.net
Posts: 13
Joined: Fri Jan 15, 2021 9:41 am

External Radio "Transmit" doesn't drop off/switch back to receive

#1

Unread post by herbk@comcast.net »

I have the TS-990S transceiver into an SPE amplifier. This is handshaking with
SDRC via OmniRig. SDRC is v3.1 and OmniRig is V1.16. The SDR is an Airspy HF+ dedicated
as a panadapter.

Strange, but something has changed, and I can't quite figure it out. If I have the
amplifier set for low output to antenna 1, and I end a transmission, the red transmit indicator
stays on so the waterfall remains muted. The external radio indicates "Not responding".

Simply opening the OmniRig settings box and acknowledging the settings (no changes)
restores the "Online" status of the external radio and all appears normal. I would guess
this is an "RFI issue", but if I switch to antenna 2 (dummy load), the external radio
behaves normally staying "Online" and switching out of transmit.

I am sure I have some digging to do but I thought I would throw it out there in the
event someone has ever run into anything similar.
73'

Max
Posts: 432
Joined: Thu Aug 13, 2020 9:47 am

Re: External Radio "Transmit" doesn't drop off/switch back to receive

#2

Unread post by Max »

Not an expert, but I've had similar issues all due to RFI getting in to the PC. I would bet money that the effect is not the same on all bands?

Only run matched antennas or with antenna tuners remote from the op position if the antennas are not well matched and also use common mode chokes on feeders, ideally at the antenna end. So easy to add and so effective. 30 min job to make and insert in lines using FT-240 Type 31 ferrite core and few turns of mini teflon coax (RG400 or similar) or even cheaper, just twisted pair wires. See here:

http://k9yc.com/2018Cookbook.pdf

Common mode chokes also reduce local noise on the receive side if that's a problem for you (it seems it is for most of us!).

73

Max

herbk@comcast.net
Posts: 13
Joined: Fri Jan 15, 2021 9:41 am

Re: External Radio "Transmit" doesn't drop off/switch back to receive

#3

Unread post by herbk@comcast.net »

Max:
Thanks for the thoughts and pointing to the KY9C "Cookbook".
You would win the bet: the "Online / Not Responding" merry-go-round I described was
when operating on 75-meters. I do not notice the same issue when on 20-meters.

The Cookbook is very detailed and I will keep it handy and work to decipher correctly
the contents. It seems spot on.
N2GEW

Max
Posts: 432
Joined: Thu Aug 13, 2020 9:47 am

Re: External Radio "Transmit" doesn't drop off/switch back to receive

#4

Unread post by Max »

herbk@comcast.net wrote:
Sun Jan 09, 2022 4:03 pm
The Cookbook is very detailed and I will keep it handy and work to decipher correctly
the contents. It seems spot on.
N2GEW
NP Herb. Glad the link is useful. There is a lot of interesting educational information in the cookbook but as far as I can see it pretty much all boils down to the choke I described, or the bifilar version using basically just regular electrical cable on the Fairite core. There is a small impedance mis-match for the bifilar version but seems (according to the booklet) that this is close to irrelevant at the HF frequencies. Just adjust the core material and number of turns to the frequency you want to choke using the tables near the end of the booklet.

Seems a lot of commercial chokes just use many ferrite rings/beads threaded over a length of coax, but you will see in the Cookbook that the type of homemade choke quickly made using FT240 torroid cores far surpasses the other type in choking ability and in a far smaller package, and a fraction of the cost. Also if you wish to choke full range 3.5 MHz to 30 MHz it's no problem to use a longer piece of mini teflon coax and wind two chokes in series, one on to type 43 ferrite and the other on to type 31 (with number of turns for each core from table to your requirements) . Does not even need putting into an enclosure so long as connections are weatherproof (if outdoors).

Also see these two links for more interesting stuff:

From Steve Hunt (sadly SK)
http://www.karinya.net/g3txq/chokes/

Jim's Power Point presentation:
http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

73

Max

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