ssg output - Page 1
Forum section: electronics / rf-microwave

author: m3vuv
author_rank: Super Contributor
timestamp: November 07, 2021, 05:42:48 am
content: hi all,i need to check my deaf kenwood ts-700g,it calls for a signal input of 10microvolt or 20 dbi,my cheap sig gen only has a coarse and fine output control,how can i adjust it for 20dbm,i have a decent marconi rf volt meter and a 50mhz scope,plus dmm etc.

author: bob91343
author_rank: Super Contributor
timestamp: November 07, 2021, 05:25:01 pm
content: You can't use a cheap sig gen for this. It has uncalibrated output and leakage. Perhaps you can borrow a good one, say a Wavetek or HP that is more proper for this task.I am in Los Angeles and could help if we are local.

author: xrunner
author_rank: Super Contributor
timestamp: November 07, 2021, 05:44:41 pm
content: As bob91343 said you really need an rf signal generator which has calibrated frequency and rf output into 50 ohms. You said it requires (for some part of the alignment) 10 uV as the input to the ant. connector. That would be -87 dBm into 50 ohms. Typically you would calibrate the S meter to indicate S9 with an antenna input of -73 dBm so that is less than that. -87 would be near ~S7.If you have another quality receiver that you trust is generally working correctly, you could set up your generator to get an S9 (-73 dBm) or S7 (-85 dBm) into that receiver and use that as a transfer standard to see if your Kenwood isnearwhat it's supposed to be. But that is just a very rough check and does not substitute for using the proper equipment. But if you want a quick and dirty sanity check you can do this. I mean for all practical purposes if you cannot hear any signals on any band with a good antenna you have a more serious issue in the rf path anyway.Make damn sure you don't input too much power. For example you said -Quote+20 dBm is 100 mW (into 50 ohms) which iswaytoo much power to inject into the receiver antenna port.I attached an S meter calibration chart if you want to see more values.

author: TimFox
author_rank: Super Contributor
timestamp: November 07, 2021, 05:48:34 pm
content: A real "standard signal generator" includes a great deal of shielding to limit the leakage from the actual oscillator circuit to the outside, including through the power line, that gets around the output attenuator. A cheap unshielded generator works when you don't need very low voltages, but adding an external attenuator after it will not give a defined output level.Also: check your units. You want 10 uV RMS, which (into 50 ohms) is 2 pW, or +33 dBf (with respect to 1 fW) or -87 dBm (with respect to 1 mW). As a voltage, it is -100 dBV (with respect to 1 V, impedance not specified).The only place I have found fW is in input specifications for FM tuners and other receivers.

author: m3vuv
author_rank: Super Contributor
timestamp: November 07, 2021, 07:19:53 pm
content: i may pull the txrx relay and clean the contacts for a start.

author: bob91343
author_rank: Super Contributor
timestamp: November 08, 2021, 02:02:48 am
content: You don't have to do that. Just connect antenna to the receiver input side of the relay.

author: xrunner
author_rank: Super Contributor
timestamp: November 08, 2021, 12:34:19 pm
content: I ran into a similar sort issue with a Kenwood R-2000 shortwave receiver just the other day. The "DX" / "Local" switch on the back (which puts an attenuation in-line from the antenna input for strong local stations) got switched by my hand accidentally. I went to eat lunch and when I came back I got nothing out of the speaker. I thought something bad happened and it took me a while to realize what it was. When I switched it back to "DX" I still got nothing until I played with the switch for a while. I put a drop of De-Oxit in there and that cleaned the switch contacts. It's probably been in the "DX" position for most of the time since the radio was made in the 1980s.

author: m3vuv
author_rank: Super Contributor
timestamp: November 09, 2021, 11:20:19 am
content: its a bit of a toss up as what to do,i had a fire about 2yrs ago and part of my antenna feed rg213 outer covering got burned,i smeard grease on it and wrapped the damaged part in tape,i assume it has water in it now,i need to lower the mast due to the high swr,i suspect the antenna has water in it too,the mast is a 30ft aluminium 2" dia pole with a 8ft co linear on top of it,it is sorounded by buildings,ie if it falls its going to damage roof tiles,its not crank up so is a 2 man job to lower,i may do that then sort the rig if needed,its a job i keep putting off!.